[PATCH 4.19 06/35] arm64: Avoid premature usercopy failure

Greg Kroah-Hartman
2021-11-01T09:24:54Z

From: Robin Murphy <robin.murphy@arm.com>

commit 295cf156231ca3f9e3a66bde7fab5e09c41835e0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Huang <chenhuang5@huawei.com>
---
arch/arm64/lib/copy_from_user.S | 13 ++++++++++---
arch/arm64/lib/copy_in_user.S | 20 ++++++++++++++------
arch/arm64/lib/copy_to_user.S | 14 +++++++++++---
3 files changed, 35 insertions(+), 12 deletions(-)

--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -39,7 +39,7 @@
.endm

.macro ldrh1 ptr, regB, val
- uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val
+ uao_user_alternative 9997f, ldrh, ldtrh, \ptr, \regB, \val
.endm

.macro strh1 ptr, regB, val
@@ -47,7 +47,7 @@
.endm

.macro ldr1 ptr, regB, val
- uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val
+ uao_user_alternative 9997f, ldr, ldtr, \ptr, \regB, \val
.endm

.macro str1 ptr, regB, val
@@ -55,7 +55,7 @@
.endm

.macro ldp1 ptr, regB, regC, val
- uao_ldp 9998f, \ptr, \regB, \regC, \val
+ uao_ldp 9997f, \ptr, \regB, \regC, \val
.endm

.macro stp1 ptr, regB, regC, val
@@ -63,9 +63,11 @@
.endm

end .req x5
+srcin .req x15
ENTRY(__arch_copy_from_user)
uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
+ mov srcin, x1
#include "copy_template.S"
uaccess_disable_not_uao x3, x4
mov x0, #0 // Nothing to copy
@@ -74,6 +76,11 @@ ENDPROC(__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
uaccess_disable_not_uao x3, x4
ret
--- a/arch/arm64/lib/copy_in_user.S
+++ b/arch/arm64/lib/copy_in_user.S
@@ -40,34 +40,36 @@
.endm

.macro ldrh1 ptr, regB, val
- uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val
+ uao_user_alternative 9997f, ldrh, ldtrh, \ptr, \regB, \val
.endm

.macro strh1 ptr, regB, val
- uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val
+ uao_user_alternative 9997f, strh, sttrh, \ptr, \regB, \val
.endm

.macro ldr1 ptr, regB, val
- uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val
+ uao_user_alternative 9997f, ldr, ldtr, \ptr, \regB, \val
.endm

.macro str1 ptr, regB, val
- uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val
+ uao_user_alternative 9997f, str, sttr, \ptr, \regB, \val
.endm

.macro ldp1 ptr, regB, regC, val
- uao_ldp 9998f, \ptr, \regB, \regC, \val
+ uao_ldp 9997f, \ptr, \regB, \regC, \val
.endm

.macro stp1 ptr, regB, regC, val
- uao_stp 9998f, \ptr, \regB, \regC, \val
+ uao_stp 9997f, \ptr, \regB, \regC, \val
.endm

end .req x5
+srcin .req x15

ENTRY(__arch_copy_in_user)
uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
+ mov srcin, x1
#include "copy_template.S"
uaccess_disable_not_uao x3, x4
mov x0, #0
@@ -76,6 +78,12 @@ ENDPROC(__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
uaccess_disable_not_uao x3, x4
ret
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -42,7 +42,7 @@
.endm

.macro strh1 ptr, regB, val
- uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val
+ uao_user_alternative 9997f, strh, sttrh, \ptr, \regB, \val
.endm

.macro ldr1 ptr, regB, val
@@ -50,7 +50,7 @@
.endm

.macro str1 ptr, regB, val
- uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val
+ uao_user_alternative 9997f, str, sttr, \ptr, \regB, \val
.endm

.macro ldp1 ptr, regB, regC, val
@@ -58,13 +58,15 @@
.endm

.macro stp1 ptr, regB, regC, val
- uao_stp 9998f, \ptr, \regB, \regC, \val
+ uao_stp 9997f, \ptr, \regB, \regC, \val
.endm

end .req x5
+srcin .req x15
ENTRY(__arch_copy_to_user)
uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
+ mov srcin, x1
#include "copy_template.S"
uaccess_disable_not_uao x3, x4
mov x0, #0
@@ -73,6 +75,12 @@ ENDPROC(__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
uaccess_disable_not_uao x3, x4
ret