RE: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof

["Kaneda, Erik" <erik.kaneda@intel.com>]

+JKim (for FreeBSD's perspective)

> -----Original Message-----
> From: Nick Desaulniers <ndesaulniers@google.com>
> Sent: Monday, June 1, 2020 4:18 PM
> To: Moore, Robert <robert.moore@intel.com>; Kaneda, Erik
> <erik.kaneda@intel.com>; Wysocki, Rafael J <rafael.j.wysocki@intel.com>;
> Len Brown <lenb@kernel.org>
> 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)

Thanks,
Erik

> 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@vger.kernel.org
> 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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