From 97fc15436b36ee3956efad83e22a557991f7d19d Mon Sep 17 00:00:00 2001 From: Kyle McMartin Date: Wed, 12 Nov 2014 21:07:44 +0000 Subject: [PATCH] arm64: __clear_user: handle exceptions on strb MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reported-by: Miloš Prchlík Cc: stable@vger.kernel.org Signed-off-by: Catalin Marinas --- arch/arm64/lib/clear_user.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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) -- 2.20.1