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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 10 Mar 2020 16:20:50 +0100
Message-ID: <CACT4Y+aV9BrvEHdaadL7FXsjMi4iPDJUnK8eyJj=HuZFa4fxuw@mail.gmail.com>
Subject: Re: [PATCH -next] lib/test_kasan: silence a -Warray-bounds warning
To:     Qian Cai <cai@lca.pw>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Mar 10, 2020 at 2:38 PM Qian Cai <cai@lca.pw> wrote:
>
> The commit "kasan: add test for invalid size in memmove" introduced a
> compilation warning where it used a negative size on purpose. Silence it
> by disabling "array-bounds" checking for this file only for testing
> purpose.
>
> In file included from ./include/linux/bitmap.h:9,
>                  from ./include/linux/cpumask.h:12,
>                  from ./arch/x86/include/asm/cpumask.h:5,
>                  from ./arch/x86/include/asm/msr.h:11,
>                  from ./arch/x86/include/asm/processor.h:22,
>                  from ./arch/x86/include/asm/cpufeature.h:5,
>                  from ./arch/x86/include/asm/thread_info.h:53,
>                  from ./include/linux/thread_info.h:38,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/rcupdate.h:27,
>                  from ./include/linux/rculist.h:11,
>                  from ./include/linux/pid.h:5,
>                  from ./include/linux/sched.h:14,
>                  from ./include/linux/uaccess.h:6,
>                  from ./arch/x86/include/asm/fpu/xstate.h:5,
>                  from ./arch/x86/include/asm/pgtable.h:26,
>                  from ./include/linux/kasan.h:15,
>                  from lib/test_kasan.c:12:
> In function 'memmove',
>     inlined from 'kmalloc_memmove_invalid_size' at
> lib/test_kasan.c:301:2:
> ./include/linux/string.h:441:9: warning: '__builtin_memmove' pointer
> overflow between offset 0 and size [-2, 9223372036854775807]
> [-Warray-bounds]
>   return __builtin_memmove(p, q, size);
>          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  lib/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/lib/Makefile b/lib/Makefile
> index ab68a8674360..24d519a0741d 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -297,6 +297,8 @@ UBSAN_SANITIZE_ubsan.o := n
>  KASAN_SANITIZE_ubsan.o := n
>  KCSAN_SANITIZE_ubsan.o := n
>  CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
> +# kmalloc_memmove_invalid_size() does this on purpose.
> +CFLAGS_test_kasan.o += $(call cc-disable-warning, array-bounds)
>
>  obj-$(CONFIG_SBITMAP) += sbitmap.o
>
> --
> 1.8.3.1
>

Acked-by: Dmitry Vyukov <dvyukov@google.com>

Thanks