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97fc15436b
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>
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|---|---|---|
| .. | ||
| bitops.S | ||
| clear_page.S | ||
| clear_user.S | ||
| copy_from_user.S | ||
| copy_in_user.S | ||
| copy_page.S | ||
| copy_to_user.S | ||
| delay.c | ||
| Makefile | ||
| memchr.S | ||
| memcmp.S | ||
| memcpy.S | ||
| memmove.S | ||
| memset.S | ||
| strchr.S | ||
| strcmp.S | ||
| strlen.S | ||
| strncmp.S | ||
| strnlen.S | ||
| strrchr.S | ||