summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorWill Deacon <will.deacon@arm.com>2019-04-08 12:45:09 +0100
committerWill Deacon <will.deacon@arm.com>2019-04-12 15:04:33 +0100
commit045afc24124d80c6998d9c770844c67912083506 (patch)
tree8e02bd1946e0704bff6f2e96ec758eb8f61b60cc
parent1e6f5440a6814d28c32d347f338bfef68bc3e69d (diff)
arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value
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@kernel.org> Fixes: 6170a97460db ("arm64: Atomic operations") Signed-off-by: Will Deacon <will.deacon@arm.com>
-rw-r--r--arch/arm64/include/asm/futex.h16
1 files changed, 8 insertions, 8 deletions
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index cccb83ad7fa8..e1d95f08f8e1 100644
--- 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: