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* [PATCH v2] arm64: atomics: lse: Dereference matching size
@ 2022-01-12 20:22 Kees Cook
  2022-01-20 15:56 ` Catalin Marinas
  0 siblings, 1 reply; 2+ messages in thread
From: Kees Cook @ 2022-01-12 20:22 UTC (permalink / raw)
  To: Will Deacon
  Cc: Kees Cook, Peter Zijlstra, Boqun Feng, Catalin Marinas,
	linux-arm-kernel, Ard Biesheuvel, Mark Rutland, linux-kernel,
	linux-hardening

When building with -Warray-bounds, the following warning is generated:

In file included from ./arch/arm64/include/asm/lse.h:16,
                 from ./arch/arm64/include/asm/cmpxchg.h:14,
                 from ./arch/arm64/include/asm/atomic.h:16,
                 from ./include/linux/atomic.h:7,
                 from ./include/asm-generic/bitops/atomic.h:5,
                 from ./arch/arm64/include/asm/bitops.h:25,
                 from ./include/linux/bitops.h:33,
                 from ./include/linux/kernel.h:22,
                 from kernel/printk/printk.c:22:
./arch/arm64/include/asm/atomic_lse.h:247:9: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'atomic_t[1]' [-Warray-bounds]
  247 |         asm volatile(                                                   \
      |         ^~~
./arch/arm64/include/asm/atomic_lse.h:266:1: note: in expansion of macro '__CMPXCHG_CASE'
  266 | __CMPXCHG_CASE(w,  , acq_, 32,  a, "memory")
      | ^~~~~~~~~~~~~~
kernel/printk/printk.c:3606:17: note: while referencing 'printk_cpulock_owner'
 3606 | static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
      |                 ^~~~~~~~~~~~~~~~~~~~

This is due to the compiler seeing an unsigned long * cast against
something (atomic_t) that is int sized. Replace the cast with the
matching size cast. This results in no change in binary output.

Note that __ll_sc__cmpxchg_case_##name##sz already uses the same
constraint:

	[v] "+Q" (*(u##sz *)ptr

Which is why only the LSE form needs updating and not the
LL/SC form, so this change is unlikely to be problematic.

Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
v1: https://lore.kernel.org/linux-hardening/20220107232746.1540130-1-keescook@chromium.org/
v2:
 - add Acks
 - note the existing LL/SC form
---
 arch/arm64/include/asm/atomic_lse.h | 2 +-
 arch/arm64/include/asm/cmpxchg.h    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h
index d955ade5df7c..5d460f6b7675 100644
--- a/arch/arm64/include/asm/atomic_lse.h
+++ b/arch/arm64/include/asm/atomic_lse.h
@@ -249,7 +249,7 @@ __lse__cmpxchg_case_##name##sz(volatile void *ptr,			\
 	"	mov	%" #w "[tmp], %" #w "[old]\n"			\
 	"	cas" #mb #sfx "\t%" #w "[tmp], %" #w "[new], %[v]\n"	\
 	"	mov	%" #w "[ret], %" #w "[tmp]"			\
-	: [ret] "+r" (x0), [v] "+Q" (*(unsigned long *)ptr),		\
+	: [ret] "+r" (x0), [v] "+Q" (*(u##sz *)ptr),			\
 	  [tmp] "=&r" (tmp)						\
 	: [old] "r" (x1), [new] "r" (x2)				\
 	: cl);								\
diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
index f9bef42c1411..497acf134d99 100644
--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -243,7 +243,7 @@ static inline void __cmpwait_case_##sz(volatile void *ptr,		\
 	"	cbnz	%" #w "[tmp], 1f\n"				\
 	"	wfe\n"							\
 	"1:"								\
-	: [tmp] "=&r" (tmp), [v] "+Q" (*(unsigned long *)ptr)		\
+	: [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr)			\
 	: [val] "r" (val));						\
 }
 
-- 
2.30.2


^ permalink raw reply related	[flat|nested] 2+ messages in thread

* Re: [PATCH v2] arm64: atomics: lse: Dereference matching size
  2022-01-12 20:22 [PATCH v2] arm64: atomics: lse: Dereference matching size Kees Cook
@ 2022-01-20 15:56 ` Catalin Marinas
  0 siblings, 0 replies; 2+ messages in thread
From: Catalin Marinas @ 2022-01-20 15:56 UTC (permalink / raw)
  To: Will Deacon, Kees Cook
  Cc: Boqun Feng, Ard Biesheuvel, Mark Rutland, linux-kernel,
	Peter Zijlstra, linux-hardening, linux-arm-kernel

On Wed, 12 Jan 2022 12:22:59 -0800, Kees Cook wrote:
> When building with -Warray-bounds, the following warning is generated:
> 
> In file included from ./arch/arm64/include/asm/lse.h:16,
>                  from ./arch/arm64/include/asm/cmpxchg.h:14,
>                  from ./arch/arm64/include/asm/atomic.h:16,
>                  from ./include/linux/atomic.h:7,
>                  from ./include/asm-generic/bitops/atomic.h:5,
>                  from ./arch/arm64/include/asm/bitops.h:25,
>                  from ./include/linux/bitops.h:33,
>                  from ./include/linux/kernel.h:22,
>                  from kernel/printk/printk.c:22:
> ./arch/arm64/include/asm/atomic_lse.h:247:9: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'atomic_t[1]' [-Warray-bounds]
>   247 |         asm volatile(                                                   \
>       |         ^~~
> ./arch/arm64/include/asm/atomic_lse.h:266:1: note: in expansion of macro '__CMPXCHG_CASE'
>   266 | __CMPXCHG_CASE(w,  , acq_, 32,  a, "memory")
>       | ^~~~~~~~~~~~~~
> kernel/printk/printk.c:3606:17: note: while referencing 'printk_cpulock_owner'
>  3606 | static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
>       |                 ^~~~~~~~~~~~~~~~~~~~
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: atomics: lse: Dereference matching size
      https://git.kernel.org/arm64/c/3364c6ce23c6

-- 
Catalin


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