A custom allocator without __GFP_COMP that copies to userspace has been
found in vmw_execbuf_process[1], so this disables the page-span checker
by placing it behind a CONFIG for future work where such things can be
tracked down later.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1373326Reported-by: NVinson Lee <vlee@freedesktop.org>
Fixes: f5509cc1 ("mm: Hardened usercopy")
Signed-off-by: NKees Cook <keescook@chromium.org>

When running with a local patch which moves the '_stext' symbol to the
very beginning of the kernel text area, I got the following panic with
CONFIG_HARDENED_USERCOPY:

  usercopy: kernel memory exposure attempt detected from ffff88103dfff000 (<linear kernel text>) (4096 bytes)
  ------------[ cut here ]------------
  kernel BUG at mm/usercopy.c:79!
  invalid opcode: 0000 [#1] SMP
  ...
  CPU: 0 PID: 4800 Comm: cp Not tainted 4.8.0-rc3.after+ #1
  Hardware name: Dell Inc. PowerEdge R720/0X3D66, BIOS 2.5.4 01/22/2016
  task: ffff880817444140 task.stack: ffff880816274000
  RIP: 0010:[<ffffffff8121c796>] __check_object_size+0x76/0x413
  RSP: 0018:ffff880816277c40 EFLAGS: 00010246
  RAX: 000000000000006b RBX: ffff88103dfff000 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: ffff88081f80dfa8 RDI: ffff88081f80dfa8
  RBP: ffff880816277c90 R08: 000000000000054c R09: 0000000000000000
  R10: 0000000000000005 R11: 0000000000000006 R12: 0000000000001000
  R13: ffff88103e000000 R14: ffff88103dffffff R15: 0000000000000001
  FS:  00007fb9d1750800(0000) GS:ffff88081f800000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00000000021d2000 CR3: 000000081a08f000 CR4: 00000000001406f0
  Stack:
   ffff880816277cc8 0000000000010000 000000043de07000 0000000000000000
   0000000000001000 ffff880816277e60 0000000000001000 ffff880816277e28
   000000000000c000 0000000000001000 ffff880816277ce8 ffffffff8136c3a6
  Call Trace:
   [<ffffffff8136c3a6>] copy_page_to_iter_iovec+0xa6/0x1c0
   [<ffffffff8136e766>] copy_page_to_iter+0x16/0x90
   [<ffffffff811970e3>] generic_file_read_iter+0x3e3/0x7c0
   [<ffffffffa06a738d>] ? xfs_file_buffered_aio_write+0xad/0x260 [xfs]
   [<ffffffff816e6262>] ? down_read+0x12/0x40
   [<ffffffffa06a61b1>] xfs_file_buffered_aio_read+0x51/0xc0 [xfs]
   [<ffffffffa06a6692>] xfs_file_read_iter+0x62/0xb0 [xfs]
   [<ffffffff812224cf>] __vfs_read+0xdf/0x130
   [<ffffffff81222c9e>] vfs_read+0x8e/0x140
   [<ffffffff81224195>] SyS_read+0x55/0xc0
   [<ffffffff81003a47>] do_syscall_64+0x67/0x160
   [<ffffffff816e8421>] entry_SYSCALL64_slow_path+0x25/0x25
  RIP: 0033:[<00007fb9d0c33c00>] 0x7fb9d0c33c00
  RSP: 002b:00007ffc9c262f28 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
  RAX: ffffffffffffffda RBX: fffffffffff8ffff RCX: 00007fb9d0c33c00
  RDX: 0000000000010000 RSI: 00000000021c3000 RDI: 0000000000000004
  RBP: 00000000021c3000 R08: 0000000000000000 R09: 00007ffc9c264d6c
  R10: 00007ffc9c262c50 R11: 0000000000000246 R12: 0000000000010000
  R13: 00007ffc9c2630b0 R14: 0000000000000004 R15: 0000000000010000
  Code: 81 48 0f 44 d0 48 c7 c6 90 4d a3 81 48 c7 c0 bb b3 a2 81 48 0f 44 f0 4d 89 e1 48 89 d9 48 c7 c7 68 16 a3 81 31 c0 e8 f4 57 f7 ff <0f> 0b 48 8d 90 00 40 00 00 48 39 d3 0f 83 22 01 00 00 48 39 c3
  RIP  [<ffffffff8121c796>] __check_object_size+0x76/0x413
   RSP <ffff880816277c40>

The checked object's range [ffff88103dfff000, ffff88103e000000) is
valid, so there shouldn't have been a BUG.  The hardened usercopy code
got confused because the range's ending address is the same as the
kernel's text starting address at 0xffff88103e000000.  The overlap check
is slightly off.

Fixes: f5509cc1 ("mm: Hardened usercopy")
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NKees Cook <keescook@chromium.org>

check_bogus_address() checked for pointer overflow using this expression,
where 'ptr' has type 'const void *':

	ptr + n < ptr

Since pointer wraparound is undefined behavior, gcc at -O2 by default
treats it like the following, which would not behave as intended:

	(long)n < 0

Fortunately, this doesn't currently happen for kernel code because kernel
code is compiled with -fno-strict-overflow.  But the expression should be
fixed anyway to use well-defined integer arithmetic, since it could be
treated differently by different compilers in the future or could be
reported by tools checking for undefined behavior.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NKees Cook <keescook@chromium.org>

This is the start of porting PAX_USERCOPY into the mainline kernel. This
is the first set of features, controlled by CONFIG_HARDENED_USERCOPY. The
work is based on code by PaX Team and Brad Spengler, and an earlier port
from Casey Schaufler. Additional non-slab page tests are from Rik van Riel.

This patch contains the logic for validating several conditions when
performing copy_to_user() and copy_from_user() on the kernel object
being copied to/from:
- address range doesn't wrap around
- address range isn't NULL or zero-allocated (with a non-zero copy size)
- if on the slab allocator:
  - object size must be less than or equal to copy size (when check is
    implemented in the allocator, which appear in subsequent patches)
- otherwise, object must not span page allocations (excepting Reserved
  and CMA ranges)
- if on the stack
  - object must not extend before/after the current process stack
  - object must be contained by a valid stack frame (when there is
    arch/build support for identifying stack frames)
- object must not overlap with kernel text
Signed-off-by: NKees Cook <keescook@chromium.org>
Tested-by: NValdis Kletnieks <valdis.kletnieks@vt.edu>
Tested-by: NMichael Ellerman <mpe@ellerman.id.au>