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Date: Mon, 12 Jul 2021 15:27:46 +0100
From: Robin Murphy <robin.murphy@....com>
To: will@...nel.org, catalin.marinas@....com
Cc: linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org,
Chen Huang <chenhuang5@...wei.com>,
Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH] arm64: Avoid premature usercopy failure
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@...r.kernel.org
Reported-by: Chen Huang <chenhuang5@...wei.com>
Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Robin Murphy <robin.murphy@....com>
---
I've started trying the "replay" approach for figuring out more precise
remainders in general, but that quickly got more complicated with
rebasing the fault address passing stuff, so I'm resending this now as
a point fix and will continue to explore that as an improvement on top.
Robin.
arch/arm64/lib/copy_from_user.S | 13 ++++++++++---
arch/arm64/lib/copy_in_user.S | 21 ++++++++++++++-------
arch/arm64/lib/copy_to_user.S | 14 +++++++++++---
3 files changed, 35 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 95cd62d67371..2cf999e41d30 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -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
diff --git a/arch/arm64/lib/copy_in_user.S b/arch/arm64/lib/copy_in_user.S
index 1f61cd0df062..dbea3799c3ef 100644
--- a/arch/arm64/lib/copy_in_user.S
+++ b/arch/arm64/lib/copy_in_user.S
@@ -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
diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 043da90f5dd7..9f380eecf653 100644
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -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
--
2.21.0.dirty
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