linux-kernel - Re: [PATCH v4 2/2] arm64: kcsan: Support detecting more missing memory barriers

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Message-ID: <YouXQ+XX8CrgM5QX@FVFF77S0Q05N>
Date:   Mon, 23 May 2022 15:16:35 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     elver@...gle.com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        arnd@...db.de
Subject: Re: [PATCH v4 2/2] arm64: kcsan: Support detecting more missing
 memory barriers

On Mon, May 23, 2022 at 07:31:26PM +0800, Kefeng Wang wrote:
> As "kcsan: Support detecting a subset of missing memory barriers"[1]
> introduced KCSAN_STRICT/KCSAN_WEAK_MEMORY which make kcsan detects
> more missing memory barrier, but arm64 don't have KCSAN instrumentation
> for barriers, so the new selftest test_barrier() and test cases for
> memory barrier instrumentation in kcsan_test module will fail, even
> panic on selftest.
> 
> Let's prefix all barriers with __ on arm64, as asm-generic/barriers.h
> defined the final instrumented version of these barriers, which will
> fix the above issues.
> 
> Note, barrier instrumentation that can be disabled via __no_kcsan with
> appropriate compiler-support (and not just with objtool help), see
> commit bd3d5bd1a0ad ("kcsan: Support WEAK_MEMORY with Clang where no
> objtool support exists"), it adds disable_sanitizer_instrumentation to
> __no_kcsan attribute which will remove all sanitizer instrumentation fully
> (with Clang 14.0). Meanwhile, GCC does the same thing with no_sanitize.
> 
> [1] https://lore.kernel.org/linux-mm/20211130114433.2580590-1-elver@google.com/
> 
> Acked-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>

Having built this with GCC 12.1.0 and LLVM 14.0.0, I think this patch itself
doesn't introduce any new problems, and logically makes sense. With that in
mind:

  Acked-by: Mark Rutland <mark.rutland@....com>

As an aside, having scanned the resulting vmlinux with objdump, there are
plenty of latent issues where we get KCSAN instrumentation where we don't want
it (e.g. early/late in arm64's entry-common.o). The bulk of those are due to
missing `nonistr` or `__always_inline`, which we'll need to fix up.

Thanks,
Mark.

> ---
>  arch/arm64/include/asm/barrier.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index 9f3e2c3d2ca0..2cfc4245d2e2 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -50,13 +50,13 @@
>  #define pmr_sync()	do {} while (0)
>  #endif
>  
> -#define mb()		dsb(sy)
> -#define rmb()		dsb(ld)
> -#define wmb()		dsb(st)
> +#define __mb()		dsb(sy)
> +#define __rmb()		dsb(ld)
> +#define __wmb()		dsb(st)
>  
> -#define dma_mb()	dmb(osh)
> -#define dma_rmb()	dmb(oshld)
> -#define dma_wmb()	dmb(oshst)
> +#define __dma_mb()	dmb(osh)
> +#define __dma_rmb()	dmb(oshld)
> +#define __dma_wmb()	dmb(oshst)
>  
>  #define io_stop_wc()	dgh()
>  
> -- 
> 2.35.3
>