Use smp_processor_id() for the generic helper bpf_get_smp_processor_id()
instead of the raw variant. This allows for preemption checks when we
have DEBUG_PREEMPT, and otherwise uses the raw variant anyway. We only
need to keep the raw variant for socket filters, but we can reuse the
helper that is already there from cBPF side.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Some minor cleanups: i) Remove the unlikely() from fd array map lookups
and let the CPU branch predictor do its job, scenarios where there is not
always a map entry are very well valid. ii) Move the attribute type check
in the bpf_perf_event_read() helper a bit earlier so it's consistent wrt
checks with bpf_perf_event_output() helper as well. iii) remove some
comments that are self-documenting in kprobe_prog_is_valid_access() and
therefore make it consistent to tp_prog_is_valid_access() as well.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The behavior of perf event arrays are quite different from all
others as they are tightly coupled to perf event fds, f.e. shown
recently by commit e03e7ee3 ("perf/bpf: Convert perf_event_array
to use struct file") to make refcounting on perf event more robust.
A remaining issue that the current code still has is that since
additions to the perf event array take a reference on the struct
file via perf_event_get() and are only released via fput() (that
cleans up the perf event eventually via perf_event_release_kernel())
when the element is either manually removed from the map from user
space or automatically when the last reference on the perf event
map is dropped. However, this leads us to dangling struct file's
when the map gets pinned after the application owning the perf
event descriptor exits, and since the struct file reference will
in such case only be manually dropped or via pinned file removal,
it leads to the perf event living longer than necessary, consuming
needlessly resources for that time.

Relations between perf event fds and bpf perf event map fds can be
rather complex. F.e. maps can act as demuxers among different perf
event fds that can possibly be owned by different threads and based
on the index selection from the program, events get dispatched to
one of the per-cpu fd endpoints. One perf event fd (or, rather a
per-cpu set of them) can also live in multiple perf event maps at
the same time, listening for events. Also, another requirement is
that perf event fds can get closed from application side after they
have been attached to the perf event map, so that on exit perf event
map will take care of dropping their references eventually. Likewise,
when such maps are pinned, the intended behavior is that a user
application does bpf_obj_get(), puts its fds in there and on exit
when fd is released, they are dropped from the map again, so the map
acts rather as connector endpoint. This also makes perf event maps
inherently different from program arrays as described in more detail
in commit c9da161c ("bpf: fix clearing on persistent program
array maps").

To tackle this, map entries are marked by the map struct file that
added the element to the map. And when the last reference to that map
struct file is released from user space, then the tracked entries
are purged from the map. This is okay, because new map struct files
instances resp. frontends to the anon inode are provided via
bpf_map_new_fd() that is called when we invoke bpf_obj_get_user()
for retrieving a pinned map, but also when an initial instance is
created via map_create(). The rest is resolved by the vfs layer
automatically for us by keeping reference count on the map's struct
file. Any concurrent updates on the map slot are fine as well, it
just means that perf_event_fd_array_release() needs to delete less
of its own entires.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch extends map_fd_get_ptr() callback that is used by fd array
maps, so that struct file pointer from the related map can be passed
in. It's safe to remove map_update_elem() callback for the two maps since
this is only allowed from syscall side, but not from eBPF programs for these
two map types. Like in per-cpu map case, bpf_fd_array_map_update_elem()
needs to be called directly here due to the extra argument.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Add a release callback for maps that is invoked when the last
reference to its struct file is gone and the struct file about
to be released by vfs. The handler will be used by fd array maps.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The ctx structure passed into bpf programs is different depending on bpf
program type. The verifier incorrectly marked ctx->data and ctx->data_end
access based on ctx offset only. That caused loads in tracing programs
int bpf_prog(struct pt_regs *ctx) { .. ctx->ax .. }
to be incorrectly marked as PTR_TO_PACKET which later caused verifier
to reject the program that was actually valid in tracing context.
Fix this by doing program type specific matching of ctx offsets.

Fixes: 969bf05e ("bpf: direct packet access")
Reported-by: NSasha Goldshtein <goldshtn@gmail.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Follow-up to commit e27f4a94 ("bpf: Use mount_nodev not mount_ns
to mount the bpf filesystem"), which removes the FS_USERNS_MOUNT flag.

The original idea was to have a per mountns instance instead of a
single global fs instance, but that didn't work out and we had to
switch to mount_nodev() model. The intent of that middle ground was
that we avoid users who don't play nice to create endless instances
of bpf fs which are difficult to control and discover from an admin
point of view, but at the same time it would have allowed us to be
more flexible with regard to namespaces.

Therefore, since we now did the switch to mount_nodev() as a fix
where individual instances are created, we also need to remove userns
mount flag along with it to avoid running into mentioned situation.
I don't expect any breakage at this early point in time with removing
the flag and we can revisit this later should the requirement for
this come up with future users. This and commit e27f4a94 have
been split to facilitate tracking should any of them run into the
unlikely case of causing a regression.

Fixes: b2197755 ("bpf: add support for persistent maps/progs")
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Humans don't write C code like:
  u8 *ptr = skb->data;
  int imm = 4;
  imm += ptr;
but from llvm backend point of view 'imm' and 'ptr' are registers and
imm += ptr may be preferred vs ptr += imm depending which register value
will be used further in the code, while verifier can only recognize ptr += imm.
That caused small unrelated changes in the C code of the bpf program to
trigger rejection by the verifier. Therefore teach the verifier to recognize
both ptr += imm and imm += ptr.
For example:
when R6=pkt(id=0,off=0,r=62) R7=imm22
after r7 += r6 instruction
will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62)

Fixes: 969bf05e ("bpf: direct packet access")
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

when packet headers are accessed in 'decreasing' order (like TCP port
may be fetched before the program reads IP src) the llvm may generate
the following code:
[...]                // R7=pkt(id=0,off=22,r=70)
r2 = *(u32 *)(r7 +0) // good access
[...]
r7 += 40             // R7=pkt(id=0,off=62,r=70)
r8 = *(u32 *)(r7 +0) // good access
[...]
r1 = *(u32 *)(r7 -20) // this one will fail though it's within a safe range
                      // it's doing *(u32*)(skb->data + 42)
Fix verifier to recognize such code pattern

Alos turned out that 'off > range' condition is not a verifier bug.
It's a buggy program that may do something like:
if (ptr + 50 > data_end)
  return 0;
ptr += 60;
*(u32*)ptr;
in such case emit
"invalid access to packet, off=0 size=4, R1(id=0,off=60,r=50)" error message,
so all information is available for the program author to fix the program.

Fixes: 969bf05e ("bpf: direct packet access")
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

While reviewing the filesystems that set FS_USERNS_MOUNT I spotted the
bpf filesystem.  Looking at the code I saw a broken usage of mount_ns
with current->nsproxy->mnt_ns. As the code does not acquire a
reference to the mount namespace it can not possibly be correct to
store the mount namespace on the superblock as it does.

Replace mount_ns with mount_nodev so that each mount of the bpf
filesystem returns a distinct instance, and the code is not buggy.

In discussion with Hannes Frederic Sowa it was reported that the use
of mount_ns was an attempt to have one bpf instance per mount
namespace, in an attempt to keep resources that pin resources from
hiding.  That intent simply does not work, the vfs is not built to
allow that kind of behavior.  Which means that the bpf filesystem
really is buggy both semantically and in it's implemenation as it does
not nor can it implement the original intent.

This change is userspace visible, but my experience with similar
filesystems leads me to believe nothing will break with a model of each
mount of the bpf filesystem is distinct from all others.

Fixes: b2197755 ("bpf: add support for persistent maps/progs")
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Start address randomization and blinding in BPF currently use
prandom_u32(). prandom_u32() values are not exposed to unpriviledged
user space to my knowledge, but given other kernel facilities such as
ASLR, stack canaries, etc make use of stronger get_random_int(), we
better make use of it here as well given blinding requests successively
new random values. get_random_int() has minimal entropy pool depletion,
is not cryptographically secure, but doesn't need to be for our use
cases here.
Suggested-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This makes perf_callchain_{user,kernel}() receive the max stack
as context for the perf_callchain_entry, instead of accessing
the global sysctl_perf_event_max_stack.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/n/tip-kolmn1yo40p7jhswxwrc7rrd@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

This work adds a generic facility for use from eBPF JIT compilers
that allows for further hardening of JIT generated images through
blinding constants. In response to the original work on BPF JIT
spraying published by Keegan McAllister [1], most BPF JITs were
changed to make images read-only and start at a randomized offset
in the page, where the rest was filled with trap instructions. We
have this nowadays in x86, arm, arm64 and s390 JIT compilers.
Additionally, later work also made eBPF interpreter images read
only for kernels supporting DEBUG_SET_MODULE_RONX, that is, x86,
arm, arm64 and s390 archs as well currently. This is done by
default for mentioned JITs when JITing is enabled. Furthermore,
we had a generic and configurable constant blinding facility on our
todo for quite some time now to further make spraying harder, and
first implementation since around netconf 2016.

We found that for systems where untrusted users can load cBPF/eBPF
code where JIT is enabled, start offset randomization helps a bit
to make jumps into crafted payload harder, but in case where larger
programs that cross page boundary are injected, we again have some
part of the program opcodes at a page start offset. With improved
guessing and more reliable payload injection, chances can increase
to jump into such payload. Elena Reshetova recently wrote a test
case for it [2, 3]. Moreover, eBPF comes with 64 bit constants, which
can leave some more room for payloads. Note that for all this,
additional bugs in the kernel are still required to make the jump
(and of course to guess right, to not jump into a trap) and naturally
the JIT must be enabled, which is disabled by default.

For helping mitigation, the general idea is to provide an option
bpf_jit_harden that admins can tweak along with bpf_jit_enable, so
that for cases where JIT should be enabled for performance reasons,
the generated image can be further hardened with blinding constants
for unpriviledged users (bpf_jit_harden == 1), with trading off
performance for these, but not for privileged ones. We also added
the option of blinding for all users (bpf_jit_harden == 2), which
is quite helpful for testing f.e. with test_bpf.ko. There are no
further e.g. hardening levels of bpf_jit_harden switch intended,
rationale is to have it dead simple to use as on/off. Since this
functionality would need to be duplicated over and over for JIT
compilers to use, which are already complex enough, we provide a
generic eBPF byte-code level based blinding implementation, which is
then just transparently JITed. JIT compilers need to make only a few
changes to integrate this facility and can be migrated one by one.

This option is for eBPF JITs and will be used in x86, arm64, s390
without too much effort, and soon ppc64 JITs, thus that native eBPF
can be blinded as well as cBPF to eBPF migrations, so that both can
be covered with a single implementation. The rule for JITs is that
bpf_jit_blind_constants() must be called from bpf_int_jit_compile(),
and in case blinding is disabled, we follow normally with JITing the
passed program. In case blinding is enabled and we fail during the
process of blinding itself, we must return with the interpreter.
Similarly, in case the JITing process after the blinding failed, we
return normally to the interpreter with the non-blinded code. Meaning,
interpreter doesn't change in any way and operates on eBPF code as
usual. For doing this pre-JIT blinding step, we need to make use of
a helper/auxiliary register, here BPF_REG_AX. This is strictly internal
to the JIT and not in any way part of the eBPF architecture. Just like
in the same way as JITs internally make use of some helper registers
when emitting code, only that here the helper register is one
abstraction level higher in eBPF bytecode, but nevertheless in JIT
phase. That helper register is needed since f.e. manually written
program can issue loads to all registers of eBPF architecture.

The core concept with the additional register is: blind out all 32
and 64 bit constants by converting BPF_K based instructions into a
small sequence from K_VAL into ((RND ^ K_VAL) ^ RND). Therefore, this
is transformed into: BPF_REG_AX := (RND ^ K_VAL), BPF_REG_AX ^= RND,
and REG <OP> BPF_REG_AX, so actual operation on the target register
is translated from BPF_K into BPF_X one that is operating on
BPF_REG_AX's content. During rewriting phase when blinding, RND is
newly generated via prandom_u32() for each processed instruction.
64 bit loads are split into two 32 bit loads to make translation and
patching not too complex. Only basic thing required by JITs is to
call the helper bpf_jit_blind_constants()/bpf_jit_prog_release_other()
pair, and to map BPF_REG_AX into an unused register.

Small bpf_jit_disasm extract from [2] when applied to x86 JIT:

echo 0 > /proc/sys/net/core/bpf_jit_harden

  ffffffffa034f5e9 + <x>:
  [...]
  39:   mov    $0xa8909090,%eax
  3e:   mov    $0xa8909090,%eax
  43:   mov    $0xa8ff3148,%eax
  48:   mov    $0xa89081b4,%eax
  4d:   mov    $0xa8900bb0,%eax
  52:   mov    $0xa810e0c1,%eax
  57:   mov    $0xa8908eb4,%eax
  5c:   mov    $0xa89020b0,%eax
  [...]

echo 1 > /proc/sys/net/core/bpf_jit_harden

  ffffffffa034f1e5 + <x>:
  [...]
  39:   mov    $0xe1192563,%r10d
  3f:   xor    $0x4989b5f3,%r10d
  46:   mov    %r10d,%eax
  49:   mov    $0xb8296d93,%r10d
  4f:   xor    $0x10b9fd03,%r10d
  56:   mov    %r10d,%eax
  59:   mov    $0x8c381146,%r10d
  5f:   xor    $0x24c7200e,%r10d
  66:   mov    %r10d,%eax
  69:   mov    $0xeb2a830e,%r10d
  6f:   xor    $0x43ba02ba,%r10d
  76:   mov    %r10d,%eax
  79:   mov    $0xd9730af,%r10d
  7f:   xor    $0xa5073b1f,%r10d
  86:   mov    %r10d,%eax
  89:   mov    $0x9a45662b,%r10d
  8f:   xor    $0x325586ea,%r10d
  96:   mov    %r10d,%eax
  [...]

As can be seen, original constants that carry payload are hidden
when enabled, actual operations are transformed from constant-based
to register-based ones, making jumps into constants ineffective.
Above extract/example uses single BPF load instruction over and
over, but of course all instructions with constants are blinded.

Performance wise, JIT with blinding performs a bit slower than just
JIT and faster than interpreter case. This is expected, since we
still get all the performance benefits from JITing and in normal
use-cases not every single instruction needs to be blinded. Summing
up all 296 test cases averaged over multiple runs from test_bpf.ko
suite, interpreter was 55% slower than JIT only and JIT with blinding
was 8% slower than JIT only. Since there are also some extremes in
the test suite, I expect for ordinary workloads that the performance
for the JIT with blinding case is even closer to JIT only case,
f.e. nmap test case from suite has averaged timings in ns 29 (JIT),
35 (+ blinding), and 151 (interpreter).

BPF test suite, seccomp test suite, eBPF sample code and various
bigger networking eBPF programs have been tested with this and were
running fine. For testing purposes, I also adapted interpreter and
redirected blinded eBPF image to interpreter and also here all tests
pass.

  [1] http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html
  [2] https://github.com/01org/jit-spray-poc-for-ksp/
  [3] http://www.openwall.com/lists/kernel-hardening/2016/05/03/5Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: NElena Reshetova <elena.reshetova@intel.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Since the blinding is strictly only called from inside eBPF JITs,
we need to change signatures for bpf_int_jit_compile() and
bpf_prog_select_runtime() first in order to prepare that the
eBPF program we're dealing with can change underneath. Hence,
for call sites, we need to return the latest prog. No functional
change in this patch.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Move the functionality to patch instructions out of the verifier
code and into the core as the new bpf_patch_insn_single() helper
will be needed later on for blinding as well. No changes in
functionality.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Besides others, remove redundant comments where the code is self
documenting enough, and properly indent various bpf_verifier_ops
and bpf_prog_type_list declarations. Moreover, remove two exports
that actually have no module user.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

since UNKNOWN_VALUE type is weaker than CONST_IMM we can un-teach
verifier its recognition of constants in conditional branches
without affecting safety.
Ex:
if (reg == 123) {
  .. here verifier was marking reg->type as CONST_IMM
     instead keep reg as UNKNOWN_VALUE
}

Two verifier states with UNKNOWN_VALUE are equivalent, whereas
CONST_IMM_X != CONST_IMM_Y, since CONST_IMM is used for stack range
verification and other cases.
So help search pruning by marking registers as UNKNOWN_VALUE
where possible instead of CONST_IMM.
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Extended BPF carried over two instructions from classic to access
packet data: LD_ABS and LD_IND. They're highly optimized in JITs,
but due to their design they have to do length check for every access.
When BPF is processing 20M packets per second single LD_ABS after JIT
is consuming 3% cpu. Hence the need to optimize it further by amortizing
the cost of 'off < skb_headlen' over multiple packet accesses.
One option is to introduce two new eBPF instructions LD_ABS_DW and LD_IND_DW
with similar usage as skb_header_pointer().
The kernel part for interpreter and x64 JIT was implemented in [1], but such
new insns behave like old ld_abs and abort the program with 'return 0' if
access is beyond linear data. Such hidden control flow is hard to workaround
plus changing JITs and rolling out new llvm is incovenient.

Therefore allow cls_bpf/act_bpf program access skb->data directly:
int bpf_prog(struct __sk_buff *skb)
{
  struct iphdr *ip;

  if (skb->data + sizeof(struct iphdr) + ETH_HLEN > skb->data_end)
      /* packet too small */
      return 0;

  ip = skb->data + ETH_HLEN;

  /* access IP header fields with direct loads */
  if (ip->version != 4 || ip->saddr == 0x7f000001)
      return 1;
  [...]
}

This solution avoids introduction of new instructions. llvm stays
the same and all JITs stay the same, but verifier has to work extra hard
to prove safety of the above program.

For XDP the direct store instructions can be allowed as well.

The skb->data is NET_IP_ALIGNED, so for common cases the verifier can check
the alignment. The complex packet parsers where packet pointer is adjusted
incrementally cannot be tracked for alignment, so allow byte access in such cases
and misaligned access on architectures that define efficient_unaligned_access

[1] https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/?h=ld_abs_dwSigned-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

cleanup verifier code and prepare it for addition of "pointer to packet" logic
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The commit 35578d79 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter")
introduced clever way to check bpf_helper<->map_type compatibility.
Later on commit a43eec30 ("bpf: introduce bpf_perf_event_output() helper") adjusted
the logic and inadvertently broke it.
Get rid of the clever bool compare and go back to two-way check
from map and from helper perspective.

Fixes: a43eec30 ("bpf: introduce bpf_perf_event_output() helper")
Reported-by: NJann Horn <jannh@google.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

On a system with >32Gbyte of phyiscal memory and infinite RLIMIT_MEMLOCK,
the malicious application may overflow 32-bit bpf program refcnt.
It's also possible to overflow map refcnt on 1Tb system.
Impose 32k hard limit which means that the same bpf program or
map cannot be shared by more than 32k processes.

Fixes: 1be7f75d ("bpf: enable non-root eBPF programs")
Reported-by: NJann Horn <jannh@google.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The default remains 127, which is good for most cases, and not even hit
most of the time, but then for some cases, as reported by Brendan, 1024+
deep frames are appearing on the radar for things like groovy, ruby.

And in some workloads putting a _lower_ cap on this may make sense. One
that is per event still needs to be put in place tho.

The new file is:

  # cat /proc/sys/kernel/perf_event_max_stack
  127

Chaging it:

  # echo 256 > /proc/sys/kernel/perf_event_max_stack
  # cat /proc/sys/kernel/perf_event_max_stack
  256

But as soon as there is some event using callchains we get:

  # echo 512 > /proc/sys/kernel/perf_event_max_stack
  -bash: echo: write error: Device or resource busy
  #

Because we only allocate the callchain percpu data structures when there
is a user, which allows for changing the max easily, its just a matter
of having no callchain users at that point.
Reported-and-Tested-by: NBrendan Gregg <brendan.d.gregg@gmail.com>
Reviewed-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDavid Ahern <dsahern@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/20160426002928.GB16708@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

When bpf(BPF_PROG_LOAD, ...) was invoked with a BPF program whose bytecode
references a non-map file descriptor as a map file descriptor, the error
handling code called fdput() twice instead of once (in __bpf_map_get() and
in replace_map_fd_with_map_ptr()). If the file descriptor table of the
current task is shared, this causes f_count to be decremented too much,
allowing the struct file to be freed while it is still in use
(use-after-free). This can be exploited to gain root privileges by an
unprivileged user.

This bug was introduced in
commit 0246e64d ("bpf: handle pseudo BPF_LD_IMM64 insn"), but is only
exploitable since
commit 1be7f75d ("bpf: enable non-root eBPF programs") because
previously, CAP_SYS_ADMIN was required to reach the vulnerable code.

(posted publicly according to request by maintainer)
Signed-off-by: NJann Horn <jannh@google.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch adds a new helper for cls/act programs that can push events
to user space applications. For networking, this can be f.e. for sampling,
debugging, logging purposes or pushing of arbitrary wake-up events. The
idea is similar to a43eec30 ("bpf: introduce bpf_perf_event_output()
helper") and 39111695 ("samples: bpf: add bpf_perf_event_output example").

The eBPF program utilizes a perf event array map that user space populates
with fds from perf_event_open(), the eBPF program calls into the helper
f.e. as skb_event_output(skb, &my_map, BPF_F_CURRENT_CPU, raw, sizeof(raw))
so that the raw data is pushed into the fd f.e. at the map index of the
current CPU.

User space can poll/mmap/etc on this and has a data channel for receiving
events that can be post-processed. The nice thing is that since the eBPF
program and user space application making use of it are tightly coupled,
they can define their own arbitrary raw data format and what/when they
want to push.

While f.e. packet headers could be one part of the meta data that is being
pushed, this is not a substitute for things like packet sockets as whole
packet is not being pushed and push is only done in a single direction.
Intention is more of a generically usable, efficient event pipe to applications.
Workflow is that tc can pin the map and applications can attach themselves
e.g. after cls/act setup to one or multiple map slots, demuxing is done by
the eBPF program.

Adding this facility is with minimal effort, it reuses the helper
introduced in a43eec30 ("bpf: introduce bpf_perf_event_output() helper")
and we get its functionality for free by overloading its BPF_FUNC_ identifier
for cls/act programs, ctx is currently unused, but will be made use of in
future. Example will be added to iproute2's BPF example files.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch converts all helpers that can use ARG_PTR_TO_RAW_STACK as argument
type. For tc programs this is bpf_skb_load_bytes(), bpf_skb_get_tunnel_key(),
bpf_skb_get_tunnel_opt(). For tracing, this optimizes bpf_get_current_comm()
and bpf_probe_read(). The check in bpf_skb_load_bytes() for MAX_BPF_STACK can
also be removed since the verifier already makes sure we stay within bounds
on stack buffers.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When passing buffers from eBPF stack space into a helper function, we have
ARG_PTR_TO_STACK argument type for helpers available. The verifier makes sure
that such buffers are initialized, within boundaries, etc.

However, the downside with this is that we have a couple of helper functions
such as bpf_skb_load_bytes() that fill out the passed buffer in the expected
success case anyway, so zero initializing them prior to the helper call is
unneeded/wasted instructions in the eBPF program that can be avoided.

Therefore, add a new helper function argument type called ARG_PTR_TO_RAW_STACK.
The idea is to skip the STACK_MISC check in check_stack_boundary() and color
the related stack slots as STACK_MISC after we checked all call arguments.

Helper functions using ARG_PTR_TO_RAW_STACK must make sure that every path of
the helper function will fill the provided buffer area, so that we cannot leak
any uninitialized stack memory. This f.e. means that error paths need to
memset() the buffers, but the expected fast-path doesn't have to do this
anymore.

Since there's no such helper needing more than at most one ARG_PTR_TO_RAW_STACK
argument, we can keep it simple and don't need to check for multiple areas.
Should in future such a use-case really appear, we have check_raw_mode() that
will make sure we implement support for it first.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Currently, when the verifier checks calls in check_call() function, we
call check_func_arg() for all 5 arguments e.g. to make sure expected types
are correct. In some cases, we collect meta data (here: map pointer) to
perform additional checks such as checking stack boundary on key/value
sizes for subsequent arguments. As we're going to extend the meta data,
add a generic struct bpf_call_arg_meta that we can use for passing into
check_func_arg().
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

verifier must check for reserved size bits in instruction opcode and
reject BPF_LD | BPF_ABS | BPF_DW and BPF_LD | BPF_IND | BPF_DW instructions,
otherwise interpreter will WARN_RATELIMIT on them during execution.

Fixes: ddd872bc ("bpf: verifier: add checks for BPF_ABS | BPF_IND instructions")
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

verifier is using the following structure to track the state of registers:
struct reg_state {
    enum bpf_reg_type type;
    union {
        int imm;
        struct bpf_map *map_ptr;
    };
};
and later on in states_equal() does memcmp(&old->regs[i], &cur->regs[i],..)
to find equivalent states.
Throughout the code of verifier there are assignements to 'imm' and 'map_ptr'
fields and it's not obvious that most of the assignments into 'imm' don't
need to clear extra 4 bytes (like mark_reg_unknown_value() does) to make sure
that memcmp doesn't go over junk left from 'map_ptr' assignment.

Simplify the code by converting 'int' into 'long'
Suggested-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The verifier needs to go through every path of the program in
order to check that it terminates safely, which can be quite a
lot of instructions that need to be processed f.e. in cases with
more branchy programs. With search pruning from f1bca824 ("bpf:
add search pruning optimization to verifier") the search space can
already be reduced significantly when the verifier detects that
a previously walked path with same register and stack contents
terminated already (see verifier's states_equal()), so the search
can skip walking those states.

When working with larger programs of > ~2000 (out of max 4096)
insns, we found that the current limit of 32k instructions is easily
hit. For example, a case we ran into is that the search space cannot
be pruned due to branches at the beginning of the program that make
use of certain stack space slots (STACK_MISC), which are never used
in the remaining program (STACK_INVALID). Therefore, the verifier
needs to walk paths for the slots in STACK_INVALID state, but also
all remaining paths with a stack structure, where the slots are in
STACK_MISC, which can nearly double the search space needed. After
various experiments, we find that a limit of 64k processed insns is
a more reasonable choice when dealing with larger programs in practice.
This still allows to reject extreme crafted cases that can have a
much higher complexity (f.e. > ~300k) within the 4096 insns limit
due to search pruning not being able to take effect.

Furthermore, we found that a lot of states can be pruned after a
call instruction, f.e. we were able to reduce the search state by
~35% in some cases with this heuristic, trade-off is to keep a bit
more states in env->explored_states. Usually, call instructions
have a number of preceding register assignments and/or stack stores,
where search pruning has a better chance to suceed in states_equal()
test. The current code marks the branch targets with STATE_LIST_MARK
in case of conditional jumps, and the next (t + 1) instruction in
case of unconditional jump so that f.e. a backjump will walk it. We
also did experiments with using t + insns[t].off + 1 as a marker in
the unconditionally jump case instead of t + 1 with the rationale
that these two branches of execution that converge after the label
might have more potential of pruning. We found that it was a bit
better, but not necessarily significantly better than the current
state, perhaps also due to clang not generating back jumps often.
Hence, we left that as is for now.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

during bpf program loading remember the last byte of ctx access
and at the time of attaching the program to tracepoint check that
the program doesn't access bytes beyond defined in tracepoint fields

This also disallows access to __dynamic_array fields, but can be
relaxed in the future.
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

needs two wrapper functions to fetch 'struct pt_regs *' to convert
tracepoint bpf context into kprobe bpf context to reuse existing
helper functions
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

... and other methods won't see them at all
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Add map_flags attribute to bpf_map_show_fdinfo(), so that tools like
tc can check for them when loading objects from a pinned entry, e.g.
if user intent wrt allocation (BPF_F_NO_PREALLOC) is different to the
pinned object, it can bail out. Follow-up to 6c905981 ("bpf:
pre-allocate hash map elements"), so that tc can still support this
with v4.6.
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Lots of places in the kernel use memcpy(buf, comm, TASK_COMM_LEN); but
the result is typically passed to print("%s", buf) and extra bytes
after zero don't cause any harm.
In bpf the result of bpf_get_current_comm() is used as the part of
map key and was causing spurious hash map mismatches.
Use strlcpy() to guarantee zero-terminated string.
bpf verifier checks that output buffer is zero-initialized,
so even for short task names the output buffer don't have junk bytes.
Note it's not a security concern, since kprobe+bpf is root only.

Fixes: ffeedafb ("bpf: introduce current->pid, tgid, uid, gid, comm accessors")
Reported-by: NTobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

0-day bot reported build error:
kernel/built-in.o: In function `map_lookup_elem':
>> kernel/bpf/.tmp_syscall.o:(.text+0x329b3c): undefined reference to `bpf_stackmap_copy'
when CONFIG_BPF_SYSCALL is set and CONFIG_PERF_EVENTS is not.
Add weak definition to resolve it.
This code path in map_lookup_elem() is never taken
when CONFIG_PERF_EVENTS is not set.

Fixes: 557c0c6e ("bpf: convert stackmap to pre-allocation")
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It was observed that calling bpf_get_stackid() from a kprobe inside
slub or from spin_unlock causes similar deadlock as with hashmap,
therefore convert stackmap to use pre-allocated memory.

The call_rcu is no longer feasible mechanism, since delayed freeing
causes bpf_get_stackid() to fail unpredictably when number of actual
stacks is significantly less than user requested max_entries.
Since elements are no longer freed into slub, we can push elements into
freelist immediately and let them be recycled.
However the very unlikley race between user space map_lookup() and
program-side recycling is possible:
     cpu0                          cpu1
     ----                          ----
user does lookup(stackidX)
starts copying ips into buffer
                                   delete(stackidX)
                                   calls bpf_get_stackid()
				   which recyles the element and
                                   overwrites with new stack trace

To avoid user space seeing a partial stack trace consisting of two
merged stack traces, do bucket = xchg(, NULL); copy; xchg(,bucket);
to preserve consistent stack trace delivery to user space.
Now we can move memset(,0) of left-over element value from critical
path of bpf_get_stackid() into slow-path of user space lookup.
Also disallow lookup() from bpf program, since it's useless and
program shouldn't be messing with collected stack trace.

Note that similar race between user space lookup and kernel side updates
is also present in hashmap, but it's not a new race. bpf programs were
always allowed to modify hash and array map elements while user space
is copying them.

Fixes: d5a3b1f6 ("bpf: introduce BPF_MAP_TYPE_STACK_TRACE")
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Suggested-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

If kprobe is placed on spin_unlock then calling kmalloc/kfree from
bpf programs is not safe, since the following dead lock is possible:
kfree->spin_lock(kmem_cache_node->lock)...spin_unlock->kprobe->
bpf_prog->map_update->kmalloc->spin_lock(of the same kmem_cache_node->lock)
and deadlocks.

The following solutions were considered and some implemented, but
eventually discarded
- kmem_cache_create for every map
- add recursion check to slow-path of slub
- use reserved memory in bpf_map_update for in_irq or in preempt_disabled
- kmalloc via irq_work

At the end pre-allocation of all map elements turned out to be the simplest
solution and since the user is charged upfront for all the memory, such
pre-allocation doesn't affect the user space visible behavior.

Since it's impossible to tell whether kprobe is triggered in a safe
location from kmalloc point of view, use pre-allocation by default
and introduce new BPF_F_NO_PREALLOC flag.

While testing of per-cpu hash maps it was discovered
that alloc_percpu(GFP_ATOMIC) has odd corner cases and often
fails to allocate memory even when 90% of it is free.
The pre-allocation of per-cpu hash elements solves this problem as well.

Turned out that bpf_map_update() quickly followed by
bpf_map_lookup()+bpf_map_delete() is very common pattern used
in many of iovisor/bcc/tools, so there is additional benefit of
pre-allocation, since such use cases are must faster.

Since all hash map elements are now pre-allocated we can remove
atomic increment of htab->count and save few more cycles.

Also add bpf_map_precharge_memlock() to check rlimit_memlock early to avoid
large malloc/free done by users who don't have sufficient limits.

Pre-allocation is done with vmalloc and alloc/free is done
via percpu_freelist. Here are performance numbers for different
pre-allocation algorithms that were implemented, but discarded
in favor of percpu_freelist:

1 cpu:
pcpu_ida	2.1M
pcpu_ida nolock	2.3M
bt		2.4M
kmalloc		1.8M
hlist+spinlock	2.3M
pcpu_freelist	2.6M

4 cpu:
pcpu_ida	1.5M
pcpu_ida nolock	1.8M
bt w/smp_align	1.7M
bt no/smp_align	1.1M
kmalloc		0.7M
hlist+spinlock	0.2M
pcpu_freelist	2.0M

8 cpu:
pcpu_ida	0.7M
bt w/smp_align	0.8M
kmalloc		0.4M
pcpu_freelist	1.5M

32 cpu:
kmalloc		0.13M
pcpu_freelist	0.49M

pcpu_ida nolock is a modified percpu_ida algorithm without
percpu_ida_cpu locks and without cross-cpu tag stealing.
It's faster than existing percpu_ida, but not as fast as pcpu_freelist.

bt is a variant of block/blk-mq-tag.c simlified and customized
for bpf use case. bt w/smp_align is using cache line for every 'long'
(similar to blk-mq-tag). bt no/smp_align allocates 'long'
bitmasks continuously to save memory. It's comparable to percpu_ida
and in some cases faster, but slower than percpu_freelist

hlist+spinlock is the simplest free list with single spinlock.
As expeceted it has very bad scaling in SMP.

kmalloc is existing implementation which is still available via
BPF_F_NO_PREALLOC flag. It's significantly slower in single cpu and
in 8 cpu setup it's 3 times slower than pre-allocation with pcpu_freelist,
but saves memory, so in cases where map->max_entries can be large
and number of map update/delete per second is low, it may make
sense to use it.
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Introduce simple percpu_freelist to keep single list of elements
spread across per-cpu singly linked lists.

/* push element into the list */
void pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);

/* pop element from the list */
struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *);

The object is pushed to the current cpu list.
Pop first trying to get the object from the current cpu list,
if it's empty goes to the neigbour cpu list.

For bpf program usage pattern the collision rate is very low,
since programs push and pop the objects typically on the same cpu.
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>