3.16.61-rc1 review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
commit 994870bead4ab19087a79492400a5478e2906196 upstream.
When an inline assembly operand's type is narrower than the register it is allocated to, the least significant bits of the register (up to the operand type's width) are valid, and any other bits are permitted to contain any arbitrary value. This aligns with the AAPCS64 parameter passing rules.
Our __smp_store_release() implementation does not account for this, and implicitly assumes that operands have been zero-extended to the width of the type being stored to. Thus, we may store unknown values to memory when the value type is narrower than the pointer type (e.g. when storing a char to a long).
This patch fixes the issue by casting the value operand to the same width as the pointer operand in all cases, which ensures that the value is zero-extended as we expect. We use the same union trickery as __smp_load_acquire and {READ,WRITE}_ONCE() to avoid GCC complaining that pointers are potentially cast to narrower width integers in unreachable paths.
A whitespace issue at the top of __smp_store_release() is also corrected.
No changes are necessary for __smp_load_acquire(). Load instructions implicitly clear any upper bits of the register, and the compiler will only consider the least significant bits of the register as valid regardless.
Fixes: 47933ad41a86 ("arch: Introduce smp_load_acquire(), smp_store_release()") Fixes: 878a84d5a8a1 ("arm64: add missing data types in smp_load_acquire/smp_store_release") Acked-by: Will Deacon will.deacon@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Matthias Kaehlcke mka@chromium.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com [bwh: The same upstream commit was already backported to 3.16, but we didn't have the 1-byte and 2-byte cases then so I dropped that part. Now that we do, pick up that part again.] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/arm64/include/asm/barrier.h | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)
--- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -66,11 +66,15 @@ do { \ switch (sizeof(*p)) { \ case 1: \ asm volatile ("stlrb %w1, %0" \ - : "=Q" (*p) : "r" (v) : "memory"); \ + : "=Q" (*p) \ + : "r" (*(__u8 *)__u.__c) \ + : "memory"); \ break; \ case 2: \ asm volatile ("stlrh %w1, %0" \ - : "=Q" (*p) : "r" (v) : "memory"); \ + : "=Q" (*p) \ + : "r" (*(__u16 *)__u.__c) \ + : "memory"); \ break; \ case 4: \ asm volatile ("stlr %w1, %0" \