linux-kernel - Re: [PATCH] ACPICA: fix UBSAN warning using __builtin

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Date:   Wed, 10 Jun 2020 19:31:30 -0400
From:   Jung-uk Kim <jkim@...eBSD.org>
To:     "Kaneda, Erik" <erik.kaneda@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "glider@...gle.com" <glider@...gle.com>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "pcc@...gle.com" <pcc@...gle.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "will@...nel.org" <will@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>
Subject: Re: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof

On 20. 6. 10., Kaneda, Erik wrote:
> +JKim (for FreeBSD's perspective)
> 
>> -----Original Message-----
>> From: Nick Desaulniers <ndesaulniers@...gle.com>
>> Sent: Monday, June 1, 2020 4:18 PM
>> To: Moore, Robert <robert.moore@...el.com>; Kaneda, Erik
>> <erik.kaneda@...el.com>; Wysocki, Rafael J <rafael.j.wysocki@...el.com>;
>> Len Brown <lenb@...nel.org>
>> Cc: Ard Biesheuvel <ardb@...nel.org>; dvyukov@...gle.com;
>> glider@...gle.com; guohanjun@...wei.com; linux-arm-
>> kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
>> lorenzo.pieralisi@....com; mark.rutland@....com;
>> ndesaulniers@...gle.com; pcc@...gle.com; rjw@...ysocki.net;
>> will@...nel.org; stable@...r.kernel.org; linux-acpi@...r.kernel.org;
>> devel@...ica.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: stable@...r.kernel.org
>> Reported-by: Will Deacon <will@...nel.org>
>> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
>> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.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
>