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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>
59 lines
1.4 KiB
ArmAsm
59 lines
1.4 KiB
ArmAsm
/*
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* Based on arch/arm/lib/clear_user.S
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*
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* Copyright (C) 2012 ARM Ltd.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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.text
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/* Prototype: int __clear_user(void *addr, size_t sz)
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* Purpose : clear some user memory
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* Params : addr - user memory address to clear
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* : sz - number of bytes to clear
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* Returns : number of bytes NOT cleared
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*
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* Alignment fixed up by hardware.
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*/
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ENTRY(__clear_user)
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mov x2, x1 // save the size for fixup return
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subs x1, x1, #8
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b.mi 2f
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1:
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USER(9f, str xzr, [x0], #8 )
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subs x1, x1, #8
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b.pl 1b
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2: adds x1, x1, #4
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b.mi 3f
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USER(9f, str wzr, [x0], #4 )
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sub x1, x1, #4
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3: adds x1, x1, #2
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b.mi 4f
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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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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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.section .fixup,"ax"
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.align 2
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9: mov x0, x2 // return the original size
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ret
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.previous
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