# RE: \[PATCH\] ACPICA: fix UBSAN warning using \_\_builtin\_offsetof

- From: Kaneda, Erik \<hidden\>
- Date: 2020-06-02 00:03:11 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/06/5986550
- Thread: https://ratatoskr.run/linux-arm-kernel/2020/05/5973580/t.md

```text


> -----Original Message-----
> From: Nick Desaulniers <ndesaulniers@google.com>
> Sent: Monday, June 1, 2020 4:18 PM
> To: Moore, Robert <redacted>; Kaneda, Erik
> [ref]; Wysocki, Rafael J [ref];
> Len Brown [ref]
> Cc: Ard Biesheuvel <ardb@kernel.org>; dvyukov@google.com;
> glider@google.com; guohanjun@huawei.com; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> lorenzo.pieralisi@arm.com; mark.rutland@arm.com;
> ndesaulniers@google.com; pcc@google.com; rjw@rjwysocki.net;
> will@kernel.org; stable@vger.kernel.org; linux-acpi@vger.kernel.org;
> devel@acpica.org
> Subject: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof
>
Hi,
 
> Will reported UBSAN warnings:
> UBSAN: null-ptr-deref in drivers/acpi/acpica/tbfadt.c:459:37
> UBSAN: null-ptr-deref in arch/arm64/kernel/smp.c:596:6
> 
> Looks like the emulated offsetof macro ACPI_OFFSET is causing these. We
> can avoid this by using the compiler builtin, __builtin_offsetof.

I'll take a look at this tomorrow
> 
> The non-kernel runtime of UBSAN would print:
> runtime error: member access within null pointer of type for this macro.

actypes.h is owned by ACPICA so we typically do not allow compiler-specific
extensions because the code is intended to be compiled using the C99 standard
without compiler extensions. We could allow this sort of thing in a Linux-specific
header file like include/acpi/platform/aclinux.h but I'll take a look at the error as well..

Erik
> 
> Link: https://lore.kernel.org/lkml/20200521100952.GA5360@willie-the-truck/
> Cc: <redacted>
> Reported-by: Will Deacon <will@kernel.org>
> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  include/acpi/actypes.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h index
> 4defed58ea33..04359c70b198 100644
> --- a/include/acpi/actypes.h
> +++ b/include/acpi/actypes.h
> @@ -508,7 +508,7 @@ typedef u64 acpi_integer;
> 
>  #define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, (acpi_size) (i))
>  #define ACPI_TO_INTEGER(p)              ACPI_PTR_DIFF (p, (void *) 0)
> -#define ACPI_OFFSET(d, f)               ACPI_PTR_DIFF (&(((d *) 0)->f), (void *)
> 0)
> +#define ACPI_OFFSET(d, f)               __builtin_offsetof(d, f)
>  #define ACPI_PHYSADDR_TO_PTR(i)         ACPI_TO_POINTER(i)
>  #define ACPI_PTR_TO_PHYSADDR(i)         ACPI_TO_INTEGER(i)
> 
> --
> 2.27.0.rc2.251.g90737beb825-goog

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