60 lines
1.8 KiB
Diff
60 lines
1.8 KiB
Diff
From 98e676789aa06582cb0d0f7758e77864b38c12a7 Mon Sep 17 00:00:00 2001
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From: Kyle McMartin <kyle@redhat.com>
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Date: Wed, 12 Nov 2014 16:07:44 -0500
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Subject: [PATCH] arm64: __clear_user: handle exceptions on strb
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ARM64 currently doesn't fix up faults on the single-byte (strb) case of
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__clear_user... which means that we can cause a nasty kernel panic as an
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ordinary user with any multiple PAGE_SIZE+1 read from /dev/zero.
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i.e.: dd if=/dev/zero of=foo ibs=1 count=1 (or ibs=65537, etc.)
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This is a pretty obscure bug in the general case since we'll only
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__do_kernel_fault (since there's no extable entry for pc) if the
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mmap_sem is contended. However, with CONFIG_DEBUG_VM enabled, we'll
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always fault.
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if (!down_read_trylock(&mm->mmap_sem)) {
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if (!user_mode(regs) && !search_exception_tables(regs->pc))
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goto no_context;
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retry:
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down_read(&mm->mmap_sem);
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} else {
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/*
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* The above down_read_trylock() might have succeeded in
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* which
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* case, we'll have missed the might_sleep() from
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* down_read().
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*/
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might_sleep();
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#ifdef CONFIG_DEBUG_VM
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if (!user_mode(regs) && !search_exception_tables(regs->pc))
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goto no_context;
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#endif
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}
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Fix that by adding an extable entry for the strb instruction, since it
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touches user memory, similar to the other stores in __clear_user.
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Signed-off-by: Kyle McMartin <kyle@redhat.com>
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Cc: stable@vger.kernel.org
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---
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arch/arm64/lib/clear_user.S | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
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index 6e0ed93d51fe..c17967fdf5f6 100644
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--- a/arch/arm64/lib/clear_user.S
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+++ b/arch/arm64/lib/clear_user.S
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@@ -46,7 +46,7 @@ USER(9f, strh wzr, [x0], #2 )
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sub x1, x1, #2
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4: adds x1, x1, #1
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b.mi 5f
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- strb wzr, [x0]
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+USER(9f, strb wzr, [x0] )
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5: mov x0, #0
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ret
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ENDPROC(__clear_user)
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--
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1.9.3
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