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

- From: Jung-uk Kim \<hidden\>
- Date: 2020-06-10 23:31:42 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/06/5996150
- Thread: https://ratatoskr.run/linux-arm-kernel/2020/05/5973580/t.md

```text
On 20. 6. 10., Kaneda, Erik wrote:
> +JKim (for FreeBSD's perspective)
> 
>> -----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
>>
>> 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
>>
> Hi,
> 
>> Looks like the emulated offsetof macro ACPI_OFFSET is causing these. We
>> can avoid this by using the compiler builtin, __builtin_offsetof.
>>
> This doesn't really fly because __builtin_offsetof is a compiler extension.
> 
> It looks like a lot of stddef.h files do this:
> 
> #define offsetof(a,b) __builtin_offset(a,b)
> 
> So does anyone have objections to ACPI_OFFSET being defined to offsetof()?
> 
> This will allow a host OS project project to use their own definitions of offsetof in place of ACPICA's.
> If they don't have a definition for offsetof, we can supply the old one as a fallback.
> 
> Here's a patch:
> 
> --- a/include/acpi/actypes.h
> +++ b/include/acpi/actypes.h
> @@ -504,11 +504,17 @@ typedef u64 acpi_integer;
>  #define ACPI_SUB_PTR(t, a, b)           ACPI_CAST_PTR (t, (ACPI_CAST_PTR (u8, (a)) - (acpi_size)(b)))
>  #define ACPI_PTR_DIFF(a, b)             ((acpi_size) (ACPI_CAST_PTR (u8, (a)) - ACPI_CAST_PTR (u8, (b))))
> 
> +/* Use an existing definiton for offsetof */
> +
> +#ifndef offsetof
> +#define offsetof(d,f)                   ACPI_PTR_DIFF (&(((d *) 0)->f), (void *) 0)
> +#endif
> +
>  /* Pointer/Integer type conversions */
> 
>  #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)               offsetof (d,f)
>  #define ACPI_PHYSADDR_TO_PTR(i)         ACPI_TO_POINTER(i)
>  #define ACPI_PTR_TO_PHYSADDR(i)         ACPI_TO_INTEGER(i)

LGTM.

Jung-uk Kim

>> 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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