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

+JKim (for FreeBSD's perspective)

quoted

-----Original Message-----
From: Nick Desaulniers <ndesaulniers@google.com>
Sent: Monday, June 1, 2020 4:18 PM
To: Moore, Robert <redacted>; Kaneda, Erik
[off-list ref]; Wysocki, Rafael J [off-list ref];
Len Brown [off-list ref]
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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,

quoted

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)