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From:   "Kaneda, Erik" <erik.kaneda@intel.com>
To:     Jung-uk Kim <jkim@FreeBSD.org>,
        Nick Desaulniers <ndesaulniers@google.com>
CC:     "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        Ard Biesheuvel <ardb@kernel.org>,
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        "will@kernel.org" <will@kernel.org>,
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        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "devel@acpica.org" <devel@acpica.org>
Subject: RE: [Devel] Re: [PATCH] ACPICA: fix UBSAN warning using
 __builtin_offsetof
Thread-Topic: [Devel] Re: [PATCH] ACPICA: fix UBSAN warning using
 __builtin_offsetof
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Date:   Thu, 11 Jun 2020 16:45:23 +0000
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> -----Original Message-----
> From: Jung-uk Kim <jkim@FreeBSD.org>
> Sent: Wednesday, June 10, 2020 4:46 PM
> To: Nick Desaulniers <ndesaulniers@google.com>; Kaneda, Erik
> <erik.kaneda@intel.com>
> Cc: Wysocki, Rafael J <rafael.j.wysocki@intel.com>; Ard Biesheuvel
> <ardb@kernel.org>; dvyukov@google.com; glider@google.com; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> lorenzo.pieralisi@arm.com; mark.rutland@arm.com; pcc@google.com;
> rjw@rjwysocki.net; will@kernel.org; stable@vger.kernel.org; linux-
> acpi@vger.kernel.org; devel@acpica.org
> Subject: [Devel] Re: [PATCH] ACPICA: fix UBSAN warning using
> __builtin_offsetof
>=20
> On 20. 6. 10., Nick Desaulniers wrote:
> > On Wed, Jun 10, 2020 at 4:07 PM Kaneda, Erik <erik.kaneda@intel.com>
> 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 <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 exten=
sion.
> >>
> >> 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 on=
e 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 */
> >
> > s/definiton/definition/
> >
> >> +
> >> +#ifndef offsetof
> >> +#define offsetof(d,f)                   ACPI_PTR_DIFF (&(((d *) 0)->f=
), (void *)
> 0)
> >> +#endif
> >
> > If this header doesn't explicitly include <stddef.h> or
> > <linux/stddef.h>, won't translation units that include
> > <acpi/actypes.h> get different definitions of ACPI_OFFSET based on
> > whether they explicitly or transitively included <stddef.h> before
> > including <acpi/actypes.h>?  Theoretically, a translation unit in the
> > kernel could include actypes.h, have no includes of linux/stddef.h,
> > then get UBSAN errors again from using this definition?
> >
> > I don't mind using offsetof in place of the builtin (since it
> > typically will be implemented in terms of the builtin, or is at least
> > for the case specific to the Linux kernel). But if it's used, we
> > should include the header that defines it properly, and we should not
> > use the host's <stddef.h> IMO.  Is there a platform specific way to
> > include the platform's stddef.h here?
> >
> > Maybe linux/stddef.h should be included in
> > include/acpi/platform/aclinux.h, then include/acpi/platform/acenv.h
> > included in include/acpi/actypes.h, such that ACPI_OFFSET is defined
> > in terms of offsetof defined from that transitive dependency of
> > headers? (or do we get a circular inclusion trying to do that?)
>=20
Hi,

> Actually, I think we should let platform-specific acfoo.h decide what to
> do here, i.e.,

That's a better solution. For Linux, it would look something like this:

--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -508,10 +508,15 @@ 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), (v=
oid *) 0)
 #define ACPI_PHYSADDR_TO_PTR(i)         ACPI_TO_POINTER(i)
 #define ACPI_PTR_TO_PHYSADDR(i)         ACPI_TO_INTEGER(i)

+/* Platforms may want to define their own ACPI_OFFSET */
+
+#ifndef ACPI_OFFSET
+#define ACPI_OFFSET(d, f)               ACPI_PTR_DIFF (&(((d *) 0)->f), (v=
oid *) 0)
+#endif
+
 /* Optimizations for 4-character (32-bit) acpi_name manipulation */

 #ifndef ACPI_MISALIGNMENT_NOT_SUPPORTED
diff --git a/include/acpi/platform/aclinux.h b/include/acpi/platform/aclinu=
x.h
index 987e2af7c335..5d1ca6015fce 100644
--- a/include/acpi/platform/aclinux.h
+++ b/include/acpi/platform/aclinux.h
@@ -71,6 +71,11 @@
 #undef ACPI_DEBUG_DEFAULT
 #define ACPI_DEBUG_DEFAULT          (ACPI_LV_INFO | ACPI_LV_REPAIR)

+/* Use gcc's builtin offset instead of the default */
+
+#undef ACPI_OFFSET
+#define ACPI_OFFSET(a,b)            __builtin_offsetof(a,b)
+
 #ifndef CONFIG_ACPI

>=20
> #ifndef ACPI_OFFSET
> #define ACPI_OFFSET(d, f) ...
> #endif
>=20
> Jung-uk Kim
>=20
> >> +
> >>  /* Pointer/Integer type conversions */
> >>
> >>  #define ACPI_TO_POINTER(i)              ACPI_CAST_PTR (void, (acpi_si=
ze) (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 mac=
ro.
> >>>
> >>> 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_s=
ize)
> (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
>=20
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