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

- From: Peter Collingbourne \<hidden\>
- Date: 2020-06-01 23:38:00 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/06/5986538
- Thread: https://ratatoskr.run/linux-arm-kernel/2020/05/5973580/t.md

```text
On Mon, Jun 1, 2020 at 4:18 PM Nick Desaulniers [ref] wrote:
>
> 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.

Would it be better to s/ACPI_OFFSET/offsetof/g the existing users of
this macro and remove it? It looks like offsetof is already being used
pervasively in the kernel, and its definition comes from
<linux/stddef.h>.

Peter


Peter

> The non-kernel runtime of UBSAN would print:
> runtime error: member access within null pointer of type
> for this macro.
>
> 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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