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authorKyle McMartin <kyle@redhat.com>2014-11-12 21:07:44 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2014-11-13 15:21:26 +0000
commit97fc15436b36ee3956efad83e22a557991f7d19d (patch)
tree15caad126a18f7e2db8f4764e3e9c08fde8c29c9 /arch/arm64/lib/clear_user.S
parentarm64: Fix data type for physical address (diff)
downloadlinux-dev-97fc15436b36ee3956efad83e22a557991f7d19d.tar.xz
linux-dev-97fc15436b36ee3956efad83e22a557991f7d19d.zip
arm64: __clear_user: handle exceptions on strb
ARM64 currently doesn't fix up faults on the single-byte (strb) case of __clear_user... which means that we can cause a nasty kernel panic as an ordinary user with any multiple PAGE_SIZE+1 read from /dev/zero. i.e.: dd if=/dev/zero of=foo ibs=1 count=1 (or ibs=65537, etc.) This is a pretty obscure bug in the general case since we'll only __do_kernel_fault (since there's no extable entry for pc) if the mmap_sem is contended. However, with CONFIG_DEBUG_VM enabled, we'll always fault. if (!down_read_trylock(&mm->mmap_sem)) { if (!user_mode(regs) && !search_exception_tables(regs->pc)) goto no_context; retry: down_read(&mm->mmap_sem); } else { /* * The above down_read_trylock() might have succeeded in * which * case, we'll have missed the might_sleep() from * down_read(). */ might_sleep(); if (!user_mode(regs) && !search_exception_tables(regs->pc)) goto no_context; } Fix that by adding an extable entry for the strb instruction, since it touches user memory, similar to the other stores in __clear_user. Signed-off-by: Kyle McMartin <kyle@redhat.com> Reported-by: Miloš Prchlík <mprchlik@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to '')
-rw-r--r--arch/arm64/lib/clear_user.S2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index 6e0ed93d51fe..c17967fdf5f6 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -46,7 +46,7 @@ USER(9f, strh wzr, [x0], #2 )
sub x1, x1, #2
4: adds x1, x1, #1
b.mi 5f
- strb wzr, [x0]
+USER(9f, strb wzr, [x0] )
5: mov x0, #0
ret
ENDPROC(__clear_user)