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arm64: Avoid premature usercopy failure

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Al reminds us that the usercopy API must only return complete failure
if absolutely nothing could be copied. Currently, if userspace does
something silly like giving us an unaligned pointer to Device memory,
or a size which overruns MTE tag bounds, we may fail to honour that
requirement when faulting on a multi-byte access even though a smaller
access could have succeeded.

Add a mitigation to the fixup routines to fall back to a single-byte
copy if we faulted on a larger access before anything has been written
to the destination, to guarantee making *some* forward progress. We
needn't be too concerned about the overall performance since this should
only occur when callers are doing something a bit dodgy in the first
place. Particularly broken userspace might still be able to trick
generic_perform_write() into an infinite loop by targeting write() at
an mmap() of some read-only device register where the fault-in load
succeeds but any store synchronously aborts such that copy_to_user() is
genuinely unable to make progress, but, well, don't do that...

CC: stable@vger.kernel.org
Reported-by: Chen Huang <chenhuang5@huawei.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/dc03d5c675731a1f24a62417dba5429ad744234e.1626098433.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Robin Murphy 2021-07-12 15:27:46 +01:00 committed by Will Deacon
parent 8cdd23c23c
commit 295cf15623
3 changed files with 35 additions and 13 deletions
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13
arch/arm64/lib/copy_from_user.S
View file

@ -29,7 +29,7 @@
.endm
.macro ldrh1 reg, ptr, val
user_ldst 9998f, ldtrh, \reg, \ptr, \val
user_ldst 9997f, ldtrh, \reg, \ptr, \val
.endm
.macro strh1 reg, ptr, val
@ -37,7 +37,7 @@
.endm
.macro ldr1 reg, ptr, val
user_ldst 9998f, ldtr, \reg, \ptr, \val
user_ldst 9997f, ldtr, \reg, \ptr, \val
.endm
.macro str1 reg, ptr, val
@ -45,7 +45,7 @@
.endm
.macro ldp1 reg1, reg2, ptr, val
user_ldp 9998f, \reg1, \reg2, \ptr, \val
user_ldp 9997f, \reg1, \reg2, \ptr, \val
.endm
.macro stp1 reg1, reg2, ptr, val
@ -53,8 +53,10 @@
.endm
end .req x5
srcin .req x15
SYM_FUNC_START(__arch_copy_from_user)
add end, x0, x2
mov srcin, x1
#include "copy_template.S"
mov x0, #0 // Nothing to copy
ret
@ -63,6 +65,11 @@ EXPORT_SYMBOL(__arch_copy_from_user)
.section .fixup,"ax"
.align 2
9997: cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
USER(9998f, ldtrb tmp1w, [srcin])
strb tmp1w, [dst], #1
9998: sub x0, end, dst // bytes not copied
ret
.previous

21
arch/arm64/lib/copy_in_user.S
View file

@ -30,33 +30,34 @@
.endm
.macro ldrh1 reg, ptr, val
user_ldst 9998f, ldtrh, \reg, \ptr, \val
user_ldst 9997f, ldtrh, \reg, \ptr, \val
.endm
.macro strh1 reg, ptr, val
user_ldst 9998f, sttrh, \reg, \ptr, \val
user_ldst 9997f, sttrh, \reg, \ptr, \val
.endm
.macro ldr1 reg, ptr, val
user_ldst 9998f, ldtr, \reg, \ptr, \val
user_ldst 9997f, ldtr, \reg, \ptr, \val
.endm
.macro str1 reg, ptr, val
user_ldst 9998f, sttr, \reg, \ptr, \val
user_ldst 9997f, sttr, \reg, \ptr, \val
.endm
.macro ldp1 reg1, reg2, ptr, val
user_ldp 9998f, \reg1, \reg2, \ptr, \val
user_ldp 9997f, \reg1, \reg2, \ptr, \val
.endm
.macro stp1 reg1, reg2, ptr, val
user_stp 9998f, \reg1, \reg2, \ptr, \val
user_stp 9997f, \reg1, \reg2, \ptr, \val
.endm
end .req x5
srcin .req x15
SYM_FUNC_START(__arch_copy_in_user)
add end, x0, x2
mov srcin, x1
#include "copy_template.S"
mov x0, #0
ret
@ -65,6 +66,12 @@ EXPORT_SYMBOL(__arch_copy_in_user)
.section .fixup,"ax"
.align 2
9997: cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
USER(9998f, ldtrb tmp1w, [srcin])
USER(9998f, sttrb tmp1w, [dst])
add dst, dst, #1
9998: sub x0, end, dst // bytes not copied
ret
.previous

14
arch/arm64/lib/copy_to_user.S
View file

@ -32,7 +32,7 @@
.endm
.macro strh1 reg, ptr, val
user_ldst 9998f, sttrh, \reg, \ptr, \val
user_ldst 9997f, sttrh, \reg, \ptr, \val
.endm
.macro ldr1 reg, ptr, val
@ -40,7 +40,7 @@
.endm
.macro str1 reg, ptr, val
user_ldst 9998f, sttr, \reg, \ptr, \val
user_ldst 9997f, sttr, \reg, \ptr, \val
.endm
.macro ldp1 reg1, reg2, ptr, val
@ -48,12 +48,14 @@
.endm
.macro stp1 reg1, reg2, ptr, val
user_stp 9998f, \reg1, \reg2, \ptr, \val
user_stp 9997f, \reg1, \reg2, \ptr, \val
.endm
end .req x5
srcin .req x15
SYM_FUNC_START(__arch_copy_to_user)
add end, x0, x2
mov srcin, x1
#include "copy_template.S"
mov x0, #0
ret
@ -62,6 +64,12 @@ EXPORT_SYMBOL(__arch_copy_to_user)
.section .fixup,"ax"
.align 2
9997: cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
ldrb tmp1w, [srcin]
USER(9998f, sttrb tmp1w, [dst])
add dst, dst, #1
9998: sub x0, end, dst // bytes not copied
ret
.previous