It is possible to take an IRQ from EL0 following a branch to a kernel
address in such a way that the IRQ is prioritised over the instruction
abort. Whilst an attacker would need to get the stars to align here,
it might be sufficient with enough calibration so perform BP hardening
in the rare case that we see a kernel address in the ELR when handling
an IRQ from EL0.
Reported-by: NDan Hettena <dhettena@nvidia.com>
Reviewed-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

Software-step and PC alignment fault exceptions have higher priority than
instruction abort exceptions, so apply the BP hardening hooks there too
if the user PC appears to reside in kernel space.
Reported-by: NDan Hettena <dhettena@nvidia.com>
Reviewed-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

In a similar manner to array_index_mask_nospec, this patch introduces an
assembly macro (mask_nospec64) which can be used to bound a value under
speculation. This macro is then used to ensure that the indirect branch
through the syscall table is bounded under speculation, with out-of-range
addresses speculating as calls to sys_io_setup (0).
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

Currently, USER_DS represents an exclusive limit while KERNEL_DS is
inclusive. In order to do some clever trickery for speculation-safe
masking, we need them both to behave equivalently - there aren't enough
bits to make KERNEL_DS exclusive, so we have precisely one option. This
also happens to correct a longstanding false negative for a range
ending on the very top byte of kernel memory.

Mark Rutland points out that we've actually got the semantics of
addresses vs. segments muddled up in most of the places we need to
amend, so shuffle the {USER,KERNEL}_DS definitions around such that we
can correct those properly instead of just pasting "-1"s everywhere.
Signed-off-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

We don't fully understand the Cavium ThunderX erratum, but it appears
that mapping the kernel as nG can lead to horrible consequences such as
attempting to execute userspace from kernel context. Since kpti isn't
enabled for these CPUs anyway, simplify the comment justifying the lack
of post_ttbr_update_workaround in the exception trampoline.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

Signed-off-by: NMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Hunter <ahh@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Avi Kivity <avi@scylladb.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Dave Watson <davejwatson@fb.com>
Cc: David Sehr <sehr@google.com>
Cc: Greg Hackmann <ghackmann@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maged Michael <maged.michael@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-api@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/20180129202020.8515-11-mathieu.desnoyers@efficios.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

With ARM64_SW_TTBR0_PAN enabled, the exception entry code checks the
active ASID to decide whether user access was enabled (non-zero ASID)
when the exception was taken. On return from exception, if user access
was previously disabled, it re-instates TTBR0_EL1 from the per-thread
saved value (updated in switch_mm() or efi_set_pgd()).

Commit 7655abb9 ("arm64: mm: Move ASID from TTBR0 to TTBR1") makes a
TTBR0_EL1 + ASID switching non-atomic. Subsequently, commit 27a921e7
("arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN") changes the
__uaccess_ttbr0_disable() function and asm macro to first write the
reserved TTBR0_EL1 followed by the ASID=0 update in TTBR1_EL1. If an
exception occurs between these two, the exception return code will
re-instate a valid TTBR0_EL1. Similar scenario can happen in
cpu_switch_mm() between setting the reserved TTBR0_EL1 and the ASID
update in cpu_do_switch_mm().

This patch reverts the entry.S check for ASID == 0 to TTBR0_EL1 and
disables the interrupts around the TTBR0_EL1 and ASID switching code in
__uaccess_ttbr0_disable(). It also ensures that, when returning from the
EFI runtime services, efi_set_pgd() doesn't leave a non-zero ASID in
TTBR1_EL1 by using uaccess_ttbr0_{enable,disable}.

The accesses to current_thread_info()->ttbr0 are updated to use
READ_ONCE/WRITE_ONCE.

As a safety measure, __uaccess_ttbr0_enable() always masks out any
existing non-zero ASID TTBR1_EL1 before writing in the new ASID.

Fixes: 27a921e7 ("arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN")
Acked-by: NWill Deacon <will.deacon@arm.com>
Reported-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: NJames Morse <james.morse@arm.com>
Tested-by: NJames Morse <james.morse@arm.com>
Co-developed-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

The trampoline page tables are positioned after the early page tables in
the kernel linker script.

As we are about to change the early page table logic to resolve the
swapper size at link time as opposed to compile time, the
SWAPPER_DIR_SIZE variable (currently used to locate the trampline)
will be rendered unsuitable for low level assembler.

This patch solves this issue by moving the trampoline before the PAN
page tables. The offset to the trampoline from ttbr1 can then be
expressed by: PAGE_SIZE + RESERVED_TTBR0_SIZE, which is available to the
entry assembler.
Tested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NSteve Capper <steve.capper@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

When CONFIG_UNMAP_KERNEL_AT_EL0 is set the SDEI entry point and the rest
of the kernel may be unmapped when we take an event. If this may be the
case, use an entry trampoline that can switch to the kernel page tables.

We can't use the provided PSTATE to determine whether to switch page
tables as we may have interrupted the kernel's entry trampoline, (or a
normal-priority event that interrupted the kernel's entry trampoline).
Instead test for a user ASID in ttbr1_el1.

Save a value in regs->addr_limit to indicate whether we need to restore
the original ASID when returning from this event. This value is only used
by do_page_fault(), which we don't call with the SDEI regs.
Signed-off-by: NJames Morse <james.morse@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

The Software Delegated Exception Interface (SDEI) is an ARM standard
for registering callbacks from the platform firmware into the OS.
This is typically used to implement RAS notifications.

Such notifications enter the kernel at the registered entry-point
with the register values of the interrupted CPU context. Because this
is not a CPU exception, it cannot reuse the existing entry code.
(crucially we don't implicitly know which exception level we interrupted),

Add the entry point to entry.S to set us up for calling into C code. If
the event interrupted code that had interrupts masked, we always return
to that location. Otherwise we pretend this was an IRQ, and use SDEI's
complete_and_resume call to return to vbar_el1 + offset.

This allows the kernel to deliver signals to user space processes. For
KVM this triggers the world switch, a quick spin round vcpu_run, then
back into the guest, unless there are pending signals.

Add sdei_mask_local_cpu() calls to the smp_send_stop() code, this covers
the panic() code-path, which doesn't invoke cpuhotplug notifiers.

Because we can interrupt entry-from/exit-to another EL, we can't trust the
value in sp_el0 or x29, even if we interrupted the kernel, in this case
the code in entry.S will save/restore sp_el0 and use the value in
__entry_task.

When we have VMAP stacks we can interrupt the stack-overflow test, which
stirs x0 into sp, meaning we have to have our own VMAP stacks. For now
these are allocated when we probe the interface. Future patches will add
refcounting hooks to allow the arch code to allocate them lazily.
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

Aliasing attacks against CPU branch predictors can allow an attacker to
redirect speculative control flow on some CPUs and potentially divulge
information from one context to another.

This patch adds initial skeleton code behind a new Kconfig option to
enable implementation-specific mitigations against these attacks for
CPUs that are affected.
Co-developed-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

We will soon need to invoke a CPU-specific function pointer after changing
page tables, so move post_ttbr_update_workaround out into C code to make
this possible.
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

Speculation attacks against the entry trampoline can potentially resteer
the speculative instruction stream through the indirect branch and into
arbitrary gadgets within the kernel.

This patch defends against these attacks by forcing a misprediction
through the return stack: a dummy BL instruction loads an entry into
the stack, so that the predicted program flow of the subsequent RET
instruction is to a branch-to-self instruction which is finally resolved
as a branch to the kernel vectors with speculation suppressed.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

The literal pool entry for identifying the vectors base is the only piece
of information in the trampoline page that identifies the true location
of the kernel.

This patch moves it into a page-aligned region of the .rodata section
and maps this adjacent to the trampoline text via an additional fixmap
entry, which protects against any accidental leakage of the trampoline
contents.
Suggested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

There are now a handful of open-coded masks to extract the ASID from a
TTBR value, so introduce a TTBR_ASID_MASK and use that instead.
Suggested-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Allow explicit disabling of the entry trampoline on the kernel command
line (kpti=off) by adding a fake CPU feature (ARM64_UNMAP_KERNEL_AT_EL0)
that can be used to toggle the alternative sequences in our entry code and
avoid use of the trampoline altogether if desired. This also allows us to
make use of a static key in arm64_kernel_unmapped_at_el0().
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

We rely on an atomic swizzling of TTBR1 when transitioning from the entry
trampoline to the kernel proper on an exception. We can't rely on this
atomicity in the face of Falkor erratum #E1003, so on affected cores we
can issue a TLB invalidation to invalidate the walk cache prior to
jumping into the kernel. There is still the possibility of a TLB conflict
here due to conflicting walk cache entries prior to the invalidation, but
this doesn't appear to be the case on these CPUs in practice.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Hook up the entry trampoline to our exception vectors so that all
exceptions from and returns to EL0 go via the trampoline, which swizzles
the vector base register accordingly. Transitioning to and from the
kernel clobbers x30, so we use tpidrro_el0 and far_el1 as scratch
registers for native tasks.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

We will need to treat exceptions from EL0 differently in kernel_ventry,
so rework the macro to take the exception level as an argument and
construct the branch target using that.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

To allow unmapping of the kernel whilst running at EL0, we need to
point the exception vectors at an entry trampoline that can map/unmap
the kernel on entry/exit respectively.

This patch adds the trampoline page, although it is not yet plugged
into the vector table and is therefore unused.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

With the ASID now installed in TTBR1, we can re-enable ARM64_SW_TTBR0_PAN
by ensuring that we switch to a reserved ASID of zero when disabling
user access and restore the active user ASID on the uaccess enable path.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

The post_ttbr0_update_workaround hook applies to any change to TTBRx_EL1.
Since we're using TTBR1 for the ASID, rename the hook to make it clearer
as to what it's doing.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Tested-by: NShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

This patch enables detection of hardware SVE support via the
cpufeatures framework, and reports its presence to the kernel and
userspace via the new ARM64_SVE cpucap and HWCAP_SVE hwcap
respectively.

Userspace can also detect SVE using ID_AA64PFR0_EL1, using the
cpufeatures MRS emulation.

When running on hardware that supports SVE, this enables runtime
kernel support for SVE, and allows user tasks to execute SVE
instructions and make of the of the SVE-specific user/kernel
interface extensions implemented by this series.
Signed-off-by: NDave Martin <Dave.Martin@arm.com>
Reviewed-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

This patch adds the core support for switching and managing the SVE
architectural state of user tasks.

Calls to the existing FPSIMD low-level save/restore functions are
factored out as new functions task_fpsimd_{save,load}(), since SVE
now dynamically may or may not need to be handled at these points
depending on the kernel configuration, hardware features discovered
at boot, and the runtime state of the task.  To make these
decisions as fast as possible, const cpucaps are used where
feasible, via the system_supports_sve() helper.

The SVE registers are only tracked for threads that have explicitly
used SVE, indicated by the new thread flag TIF_SVE.  Otherwise, the
FPSIMD view of the architectural state is stored in
thread.fpsimd_state as usual.

When in use, the SVE registers are not stored directly in
thread_struct due to their potentially large and variable size.
Because the task_struct slab allocator must be configured very
early during kernel boot, it is also tricky to configure it
correctly to match the maximum vector length provided by the
hardware, since this depends on examining secondary CPUs as well as
the primary.  Instead, a pointer sve_state in thread_struct points
to a dynamically allocated buffer containing the SVE register data,
and code is added to allocate and free this buffer at appropriate
times.

TIF_SVE is set when taking an SVE access trap from userspace, if
suitable hardware support has been detected.  This enables SVE for
the thread: a subsequent return to userspace will disable the trap
accordingly.  If such a trap is taken without sufficient system-
wide hardware support, SIGILL is sent to the thread instead as if
an undefined instruction had been executed: this may happen if
userspace tries to use SVE in a system where not all CPUs support
it for example.

The kernel will clear TIF_SVE and disable SVE for the thread
whenever an explicit syscall is made by userspace.  For backwards
compatibility reasons and conformance with the spirit of the base
AArch64 procedure call standard, the subset of the SVE register
state that aliases the FPSIMD registers is still preserved across a
syscall even if this happens.  The remainder of the SVE register
state logically becomes zero at syscall entry, though the actual
zeroing work is currently deferred until the thread next tries to
use SVE, causing another trap to the kernel.  This implementation
is suboptimal: in the future, the fastpath case may be optimised
to zero the registers in-place and leave SVE enabled for the task,
where beneficial.

TIF_SVE is also cleared in the following slowpath cases, which are
taken as reasonable hints that the task may no longer use SVE:
 * exec
 * fork and clone

Code is added to sync data between thread.fpsimd_state and
thread.sve_state whenever enabling/disabling SVE, in a manner
consistent with the SVE architectural programmer's model.
Signed-off-by: NDave Martin <Dave.Martin@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Alex Bennée <alex.bennee@linaro.org>
[will: added #include to fix allnoconfig build]
[will: use enable_daif in do_sve_acc]
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Today SError is taken using the inv_entry macro that ends up in
bad_mode.

SError can be used by the RAS Extensions to notify either the OS or
firmware of CPU problems, some of which may have been corrected.

To allow this handling to be added, add a do_serror() C function
that just panic()s. Add the entry.S boiler plate to save/restore the
CPU registers and unmask debug exceptions. Future patches may change
do_serror() to return if the SError Interrupt was notification of a
corrected error.
Signed-off-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NWang Xiongfeng <wangxiongfengi2@huawei.com>
[Split out of a bigger patch, added compat path, renamed, enabled debug
 exceptions]
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

Following our 'dai' order, irqs should be processed with debug and
serror exceptions unmasked.

Add a helper to unmask these two, (and fiq for good measure).
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJulien Thierry <julien.thierry@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

el0_sync also unmasks exceptions on a case-by-case basis, debug exceptions
are enabled, unless this was a debug exception. Irqs are unmasked for
some exception types but not for others.

el0_dbg should run with everything masked to prevent us taking a debug
exception from do_debug_exception. For the other cases we can unmask
everything. This changes the behaviour of fpsimd_{acc,exc} and el0_inv
which previously ran with irqs masked.

This patch removed the last user of enable_dbg_and_irq, remove it.
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJulien Thierry <julien.thierry@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

el1_sync unmasks exceptions on a case-by-case basis, debug exceptions
are unmasked, unless this was a debug exception. IRQs are unmasked
for instruction and data aborts only if the interupted context had
irqs unmasked.

Following our 'dai' order, el1_dbg should run with everything masked.
For the other cases we can inherit whatever we interrupted.

Add a macro inherit_daif to set daif based on the interrupted pstate.
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJulien Thierry <julien.thierry@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

To take RAS Exceptions as quickly as possible we need to keep SError
unmasked as much as possible. We need to mask it during kernel_exit
as taking an error from this code will overwrite the exception-registers.

Adding a naked 'disable_daif' to kernel_exit causes a performance problem
for micro-benchmarks that do no real work, (e.g. calling getpid() in a
loop). This is because the ret_to_user loop has already masked IRQs so
that the TIF_WORK_MASK thread flags can't change underneath it, adding
disable_daif is an additional self-synchronising operation.

In the future, the RAS APEI code may need to modify the TIF_WORK_MASK
flags from an SError, in which case the ret_to_user loop must mask SError
while it examines the flags.

Disable all exceptions for return to EL1. For return to EL0 get the
ret_to_user loop to leave all exceptions masked once it has done its
work, this avoids an extra pstate-write.
Signed-off-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJulien Thierry <julien.thierry@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

ILP32 series [1] introduces the dependency on <asm/is_compat.h> for
TASK_SIZE macro. Which in turn requires <asm/thread_info.h>, and
<asm/thread_info.h> include <asm/memory.h>, giving a circular dependency,
because TASK_SIZE is currently located in <asm/memory.h>.

In other architectures, TASK_SIZE is defined in <asm/processor.h>, and
moving TASK_SIZE there fixes the problem.

Discussion: https://patchwork.kernel.org/patch/9929107/

[1] https://github.com/norov/linux/tree/ilp32-next

CC: Will Deacon <will.deacon@arm.com>
CC: Laura Abbott <labbott@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Suggested-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NYury Norov <ynorov@caviumnetworks.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

This patch adds stack overflow detection to arm64, usable when vmap'd stacks
are in use.

Overflow is detected in a small preamble executed for each exception entry,
which checks whether there is enough space on the current stack for the general
purpose registers to be saved. If there is not enough space, the overflow
handler is invoked on a per-cpu overflow stack. This approach preserves the
original exception information in ESR_EL1 (and where appropriate, FAR_EL1).

Task and IRQ stacks are aligned to double their size, enabling overflow to be
detected with a single bit test. For example, a 16K stack is aligned to 32K,
ensuring that bit 14 of the SP must be zero. On an overflow (or underflow),
this bit is flipped. Thus, overflow (of less than the size of the stack) can be
detected by testing whether this bit is set.

The overflow check is performed before any attempt is made to access the
stack, avoiding recursive faults (and the loss of exception information
these would entail). As logical operations cannot be performed on the SP
directly, the SP is temporarily swapped with a general purpose register
using arithmetic operations to enable the test to be performed.

This gives us a useful error message on stack overflow, as can be trigger with
the LKDTM overflow test:

[  305.388749] lkdtm: Performing direct entry OVERFLOW
[  305.395444] Insufficient stack space to handle exception!
[  305.395482] ESR: 0x96000047 -- DABT (current EL)
[  305.399890] FAR: 0xffff00000a5e7f30
[  305.401315] Task stack:     [0xffff00000a5e8000..0xffff00000a5ec000]
[  305.403815] IRQ stack:      [0xffff000008000000..0xffff000008004000]
[  305.407035] Overflow stack: [0xffff80003efce4e0..0xffff80003efcf4e0]
[  305.409622] CPU: 0 PID: 1219 Comm: sh Not tainted 4.13.0-rc3-00021-g9636aea #5
[  305.412785] Hardware name: linux,dummy-virt (DT)
[  305.415756] task: ffff80003d051c00 task.stack: ffff00000a5e8000
[  305.419221] PC is at recursive_loop+0x10/0x48
[  305.421637] LR is at recursive_loop+0x38/0x48
[  305.423768] pc : [<ffff00000859f330>] lr : [<ffff00000859f358>] pstate: 40000145
[  305.428020] sp : ffff00000a5e7f50
[  305.430469] x29: ffff00000a5e8350 x28: ffff80003d051c00
[  305.433191] x27: ffff000008981000 x26: ffff000008f80400
[  305.439012] x25: ffff00000a5ebeb8 x24: ffff00000a5ebeb8
[  305.440369] x23: ffff000008f80138 x22: 0000000000000009
[  305.442241] x21: ffff80003ce65000 x20: ffff000008f80188
[  305.444552] x19: 0000000000000013 x18: 0000000000000006
[  305.446032] x17: 0000ffffa2601280 x16: ffff0000081fe0b8
[  305.448252] x15: ffff000008ff546d x14: 000000000047a4c8
[  305.450246] x13: ffff000008ff7872 x12: 0000000005f5e0ff
[  305.452953] x11: ffff000008ed2548 x10: 000000000005ee8d
[  305.454824] x9 : ffff000008545380 x8 : ffff00000a5e8770
[  305.457105] x7 : 1313131313131313 x6 : 00000000000000e1
[  305.459285] x5 : 0000000000000000 x4 : 0000000000000000
[  305.461781] x3 : 0000000000000000 x2 : 0000000000000400
[  305.465119] x1 : 0000000000000013 x0 : 0000000000000012
[  305.467724] Kernel panic - not syncing: kernel stack overflow
[  305.470561] CPU: 0 PID: 1219 Comm: sh Not tainted 4.13.0-rc3-00021-g9636aea #5
[  305.473325] Hardware name: linux,dummy-virt (DT)
[  305.475070] Call trace:
[  305.476116] [<ffff000008088ad8>] dump_backtrace+0x0/0x378
[  305.478991] [<ffff000008088e64>] show_stack+0x14/0x20
[  305.481237] [<ffff00000895a178>] dump_stack+0x98/0xb8
[  305.483294] [<ffff0000080c3288>] panic+0x118/0x280
[  305.485673] [<ffff0000080c2e9c>] nmi_panic+0x6c/0x70
[  305.486216] [<ffff000008089710>] handle_bad_stack+0x118/0x128
[  305.486612] Exception stack(0xffff80003efcf3a0 to 0xffff80003efcf4e0)
[  305.487334] f3a0: 0000000000000012 0000000000000013 0000000000000400 0000000000000000
[  305.488025] f3c0: 0000000000000000 0000000000000000 00000000000000e1 1313131313131313
[  305.488908] f3e0: ffff00000a5e8770 ffff000008545380 000000000005ee8d ffff000008ed2548
[  305.489403] f400: 0000000005f5e0ff ffff000008ff7872 000000000047a4c8 ffff000008ff546d
[  305.489759] f420: ffff0000081fe0b8 0000ffffa2601280 0000000000000006 0000000000000013
[  305.490256] f440: ffff000008f80188 ffff80003ce65000 0000000000000009 ffff000008f80138
[  305.490683] f460: ffff00000a5ebeb8 ffff00000a5ebeb8 ffff000008f80400 ffff000008981000
[  305.491051] f480: ffff80003d051c00 ffff00000a5e8350 ffff00000859f358 ffff00000a5e7f50
[  305.491444] f4a0: ffff00000859f330 0000000040000145 0000000000000000 0000000000000000
[  305.492008] f4c0: 0001000000000000 0000000000000000 ffff00000a5e8350 ffff00000859f330
[  305.493063] [<ffff00000808205c>] __bad_stack+0x88/0x8c
[  305.493396] [<ffff00000859f330>] recursive_loop+0x10/0x48
[  305.493731] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.494088] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.494425] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.494649] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.494898] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.495205] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.495453] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.495708] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.496000] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.496302] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.496644] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.496894] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.497138] [<ffff00000859f358>] recursive_loop+0x38/0x48
[  305.497325] [<ffff00000859f3dc>] lkdtm_OVERFLOW+0x14/0x20
[  305.497506] [<ffff00000859f314>] lkdtm_do_action+0x1c/0x28
[  305.497786] [<ffff00000859f178>] direct_entry+0xe0/0x170
[  305.498095] [<ffff000008345568>] full_proxy_write+0x60/0xa8
[  305.498387] [<ffff0000081fb7f4>] __vfs_write+0x1c/0x128
[  305.498679] [<ffff0000081fcc68>] vfs_write+0xa0/0x1b0
[  305.498926] [<ffff0000081fe0fc>] SyS_write+0x44/0xa0
[  305.499182] Exception stack(0xffff00000a5ebec0 to 0xffff00000a5ec000)
[  305.499429] bec0: 0000000000000001 000000001c4cf5e0 0000000000000009 000000001c4cf5e0
[  305.499674] bee0: 574f4c465245564f 0000000000000000 0000000000000000 8000000080808080
[  305.499904] bf00: 0000000000000040 0000000000000038 fefefeff1b4bc2ff 7f7f7f7f7f7fff7f
[  305.500189] bf20: 0101010101010101 0000000000000000 000000000047a4c8 0000000000000038
[  305.500712] bf40: 0000000000000000 0000ffffa2601280 0000ffffc63f6068 00000000004b5000
[  305.501241] bf60: 0000000000000001 000000001c4cf5e0 0000000000000009 000000001c4cf5e0
[  305.501791] bf80: 0000000000000020 0000000000000000 00000000004b5000 000000001c4cc458
[  305.502314] bfa0: 0000000000000000 0000ffffc63f7950 000000000040a3c4 0000ffffc63f70e0
[  305.502762] bfc0: 0000ffffa2601268 0000000080000000 0000000000000001 0000000000000040
[  305.503207] bfe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[  305.503680] [<ffff000008082fb0>] el0_svc_naked+0x24/0x28
[  305.504720] Kernel Offset: disabled
[  305.505189] CPU features: 0x002082
[  305.505473] Memory Limit: none
[  305.506181] ---[ end Kernel panic - not syncing: kernel stack overflow

This patch was co-authored by Ard Biesheuvel and Mark Rutland.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>

We allocate our IRQ stacks using a percpu array. This allows us to generate our
IRQ stack pointers with adr_this_cpu, but bloats the kernel Image with the boot
CPU's IRQ stack. Additionally, these are packed with other percpu variables,
and aren't guaranteed to have guard pages.

When we enable VMAP_STACK we'll want to vmap our IRQ stacks also, in order to
provide guard pages and to permit more stringent alignment requirements. Doing
so will require that we use a percpu pointer to each IRQ stack, rather than
allocating a percpu IRQ stack in the kernel image.

This patch updates our IRQ stack code to use a percpu pointer to the base of
each IRQ stack. This will allow us to change the way the stack is allocated
with minimal changes elsewhere. In some cases we may try to backtrace before
the IRQ stack pointers are initialised, so on_irq_stack() is updated to account
for this.

In testing with cyclictest, there was no measureable difference between using
adr_this_cpu (for irq_stack) and ldr_this_cpu (for irq_stack_ptr) in the IRQ
entry path.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>

In subsequent patches, we will detect stack overflow in our exception
entry code, by verifying the SP after it has been decremented to make
space for the exception regs.

This verification code is small, and we can minimize its impact by
placing it directly in the vectors. To avoid redundant modification of
the SP, we also need to move the initial decrement of the SP into the
vectors.

As a preparatory step, this patch introduces kernel_ventry, which
performs this decrement, and updates the entry code accordingly.
Subsequent patches will fold SP verification into kernel_ventry.

There should be no functional change as a result of this patch.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
[Mark: turn into prep patch, expand commit msg]
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>

For historical reasons, we leave the top 16 bytes of our task and IRQ
stacks unused, a practice used to ensure that the SP can always be
masked to find the base of the current stack (historically, where
thread_info could be found).

However, this is not necessary, as:

* When an exception is taken from a task stack, we decrement the SP by
  S_FRAME_SIZE and stash the exception registers before we compare the
  SP against the task stack. In such cases, the SP must be at least
  S_FRAME_SIZE below the limit, and can be safely masked to determine
  whether the task stack is in use.

* When transitioning to an IRQ stack, we'll place a dummy frame onto the
  IRQ stack before enabling asynchronous exceptions, or executing code
  we expect to trigger faults. Thus, if an exception is taken from the
  IRQ stack, the SP must be at least 16 bytes below the limit.

* We no longer mask the SP to find the thread_info, which is now found
  via sp_el0. Note that historically, the offset was critical to ensure
  that cpu_switch_to() found the correct stack for new threads that
  hadn't yet executed ret_from_fork().

Given that, this initial offset serves no purpose, and can be removed.
This brings us in-line with other architectures (e.g. x86) which do not
rely on this masking.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
[Mark: rebase, kill THREAD_START_SP, commit msg additions]
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Tested-by: NLaura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>

As it turns out, the unwind code is slightly broken, and probably has
been for a while. The problem is in the dumping of the exception stack,
which is intended to dump the contents of the pt_regs struct at each
level in the call stack where an exception was taken and routed to a
routine marked as __exception (which means its stack frame is right
below the pt_regs struct on the stack).

'Right below the pt_regs struct' is ill defined, though: the unwind
code assigns 'frame pointer + 0x10' to the .sp member of the stackframe
struct at each level, and dump_backtrace() happily dereferences that as
the pt_regs pointer when encountering an __exception routine. However,
the actual size of the stack frame created by this routine (which could
be one of many __exception routines we have in the kernel) is not known,
and so frame.sp is pretty useless to figure out where struct pt_regs
really is.

So it seems the only way to ensure that we can find our struct pt_regs
when walking the stack frames is to put it at a known fixed offset of
the stack frame pointer that is passed to such __exception routines.
The simplest way to do that is to put it inside pt_regs itself, which is
the main change implemented by this patch. As a bonus, doing this allows
us to get rid of a fair amount of cruft related to walking from one stack
to the other, which is especially nice since we intend to introduce yet
another stack for overflow handling once we add support for vmapped
stacks. It also fixes an inconsistency where we only add a stack frame
pointing to ELR_EL1 if we are executing from the IRQ stack but not when
we are executing from the task stack.

To consistly identify exceptions regs even in the presence of exceptions
taken from entry code, we must check whether the next frame was created
by entry text, rather than whether the current frame was crated by
exception text.

To avoid backtracing using PCs that fall in the idmap, or are controlled
by userspace, we must explcitly zero the FP and LR in startup paths, and
must ensure that the frame embedded in pt_regs is zeroed upon entry from
EL0. To avoid these NULL entries showin in the backtrace, unwind_frame()
is updated to avoid them.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
[Mark: compare current frame against .entry.text, avoid bogus PCs]
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>

Currently, cpu_switch_to and ret_from_fork both live in .entry.text,
though neither form the critical path for an exception entry.

In subsequent patches, we will require that code in .entry.text is part
of the critical path for exception entry, for which we can assume
certain properties (e.g. the presence of exception regs on the stack).

Neither cpu_switch_to nor ret_from_fork will meet these requirements, so
we must move them out of .entry.text. To ensure that neither are kprobed
after being moved out of .entry.text, we must explicitly blacklist them,
requiring a new NOKPROBE() asm helper.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>

In most cases, our exception entry assembly branches to C handlers with
a BL instruction, but in cases where we do not expect to return, we use
B instead.

While this is correct today, it means that backtraces for fatal
exceptions miss the entry assembly (as the LR is stale at the point we
call C code), while non-fatal exceptions have the entry assembly in the
LR. In subsequent patches, we will need the LR to be set in these cases
in order to backtrace reliably.

This patch updates these sites to use a BL, ensuring consistency, and
preparing for backtrace rework. An ASM_BUG() is added after each of
these new BLs, which both catches unexpected returns, and ensures that
the LR value doesn't point to another function label.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>

The -1 "no syscall" value is written in various ways, shared with
the user ABI in some places, and generally obscure.

This patch attempts to make things a little more consistent and
readable by replacing all these uses with a single #define.  A
couple of symbolic helpers are provided to clarify the intent
further.

Because the in-syscall check in do_signal() is changed from >= 0 to
!= NO_SYSCALL by this patch, different behaviour may be observable
if syscallno is set to values less than -1 by a tracer.  However,
this is not different from the behaviour that is already observable
if a tracer sets syscallno to a value >= __NR_(compat_)syscalls.

It appears that this can cause spurious syscall restarting, but
that is not a new behaviour either, and does not appear harmful.
Signed-off-by: NDave Martin <Dave.Martin@arm.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

The upper 32 bits of the syscallno field in thread_struct are
handled inconsistently, being sometimes zero extended and sometimes
sign-extended.  In fact, only the lower 32 bits seem to have any
real significance for the behaviour of the code: it's been OK to
handle the upper bits inconsistently because they don't matter.

Currently, the only place I can find where those bits are
significant is in calling trace_sys_enter(), which may be
unintentional: for example, if a compat tracer attempts to cancel a
syscall by passing -1 to (COMPAT_)PTRACE_SET_SYSCALL at the
syscall-enter-stop, it will be traced as syscall 4294967295
rather than -1 as might be expected (and as occurs for a native
tracer doing the same thing).  Elsewhere, reads of syscallno cast
it to an int or truncate it.

There's also a conspicuous amount of code and casting to bodge
around the fact that although semantically an int, syscallno is
stored as a u64.

Let's not pretend any more.

In order to preserve the stp x instruction that stores the syscall
number in entry.S, this patch special-cases the layout of struct
pt_regs for big endian so that the newly 32-bit syscallno field
maps onto the low bits of the stored value.  This is not beautiful,
but benchmarking of the getpid syscall on Juno suggests indicates a
minor slowdown if the stp is split into an stp x and stp w.
Signed-off-by: NDave Martin <Dave.Martin@arm.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

When handling a data abort from EL0, we currently zero the top byte of
the faulting address, as we assume the address is a TTBR0 address, which
may contain a non-zero address tag. However, the address may be a TTBR1
address, in which case we should not zero the top byte. This patch fixes
that. The effect is that the full TTBR1 address is passed to the task's
signal handler (or printed out in the kernel log).

When handling a data abort from EL1, we leave the faulting address
intact, as we assume it's either a TTBR1 address or a TTBR0 address with
tag 0x00. This is true as far as I'm aware, we don't seem to access a
tagged TTBR0 address anywhere in the kernel. Regardless, it's easy to
forget about address tags, and code added in the future may not always
remember to remove tags from addresses before accessing them. So add tag
handling to the EL1 data abort handler as well. This also makes it
consistent with the EL0 data abort handler.

Fixes: d50240a5 ("arm64: mm: permit use of tagged pointers at EL0")
Cc: <stable@vger.kernel.org> # 3.12.x-
Reviewed-by: NDave Martin <Dave.Martin@arm.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NKristina Martsenko <kristina.martsenko@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>