This is a note to let you know that I've just added the patch titled
arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-futex-fix-futex_wake_op-atomic-ops-with-non-zero-result-value.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 045afc24124d80c6998d9c770844c67912083506 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@xxxxxxx>
Date: Mon, 8 Apr 2019 12:45:09 +0100
Subject: arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value
From: Will Deacon <will.deacon@xxxxxxx>
commit 045afc24124d80c6998d9c770844c67912083506 upstream.
Rather embarrassingly, our futex() FUTEX_WAKE_OP implementation doesn't
explicitly set the return value on the non-faulting path and instead
leaves it holding the result of the underlying atomic operation. This
means that any FUTEX_WAKE_OP atomic operation which computes a non-zero
value will be reported as having failed. Regrettably, I wrote the buggy
code back in 2011 and it was upstreamed as part of the initial arm64
support in 2012.
The reasons we appear to get away with this are:
1. FUTEX_WAKE_OP is rarely used and therefore doesn't appear to get
exercised by futex() test applications
2. If the result of the atomic operation is zero, the system call
behaves correctly
3. Prior to version 2.25, the only operation used by GLIBC set the
futex to zero, and therefore worked as expected. From 2.25 onwards,
FUTEX_WAKE_OP is not used by GLIBC at all.
Fix the implementation by ensuring that the return value is either 0
to indicate that the atomic operation completed successfully, or -EFAULT
if we encountered a fault when accessing the user mapping.
Cc: <stable@xxxxxxxxxx>
Fixes: 6170a97460db ("arm64: Atomic operations")
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/futex.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -30,8 +30,8 @@ do { \
" prfm pstl1strm, %2\n" \
"1: ldxr %w1, %2\n" \
insn "\n" \
-"2: stlxr %w3, %w0, %2\n" \
-" cbnz %w3, 1b\n" \
+"2: stlxr %w0, %w3, %2\n" \
+" cbnz %w0, 1b\n" \
" dmb ish\n" \
"3:\n" \
" .pushsection .fixup,\"ax\"\n" \
@@ -50,30 +50,30 @@ do { \
static inline int
arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *_uaddr)
{
- int oldval = 0, ret, tmp;
+ int oldval, ret, tmp;
u32 __user *uaddr = __uaccess_mask_ptr(_uaddr);
pagefault_disable();
switch (op) {
case FUTEX_OP_SET:
- __futex_atomic_op("mov %w0, %w4",
+ __futex_atomic_op("mov %w3, %w4",
ret, oldval, uaddr, tmp, oparg);
break;
case FUTEX_OP_ADD:
- __futex_atomic_op("add %w0, %w1, %w4",
+ __futex_atomic_op("add %w3, %w1, %w4",
ret, oldval, uaddr, tmp, oparg);
break;
case FUTEX_OP_OR:
- __futex_atomic_op("orr %w0, %w1, %w4",
+ __futex_atomic_op("orr %w3, %w1, %w4",
ret, oldval, uaddr, tmp, oparg);
break;
case FUTEX_OP_ANDN:
- __futex_atomic_op("and %w0, %w1, %w4",
+ __futex_atomic_op("and %w3, %w1, %w4",
ret, oldval, uaddr, tmp, ~oparg);
break;
case FUTEX_OP_XOR:
- __futex_atomic_op("eor %w0, %w1, %w4",
+ __futex_atomic_op("eor %w3, %w1, %w4",
ret, oldval, uaddr, tmp, oparg);
break;
default:
Patches currently in stable-queue which might be from will.deacon@xxxxxxx are
queue-4.19/arm64-futex-fix-futex_wake_op-atomic-ops-with-non-zero-result-value.patch
queue-4.19/arm64-kaslr-reserve-size-of-arm64_memstart_align-in-.patch
queue-4.19/arm64-backtrace-don-t-bother-trying-to-unwind-the-userspace-stack.patch
