Commit 55228db2 authored by YingChi Long's avatar YingChi Long Committed by Borislav Petkov
Browse files

x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN 

WG14 N2350 specifies that it is an undefined behavior to have type
definitions within offsetof", see

  https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm



This specification is also part of C23.

Therefore, replace the TYPE_ALIGN macro with the _Alignof builtin to
avoid undefined behavior. (_Alignof itself is C11 and the kernel is
built with -gnu11).

ISO C11 _Alignof is subtly different from the GNU C extension
__alignof__. Latter is the preferred alignment and _Alignof the
minimal alignment. For long long on x86 these are 8 and 4
respectively.

The macro TYPE_ALIGN's behavior matches _Alignof rather than
__alignof__.

  [ bp: Massage commit message. ]

Signed-off-by: default avatarYingChi Long <me@inclyc.cn>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220925153151.2467884-1-me@inclyc.cn
parent 6ea25770

arch/x86/kernel/fpu/init.c

+2 −5
Original line number Diff line number Diff line
@@ -133,9 +133,6 @@ static void __init fpu__init_system_generic(void) 
	fpu__init_system_mxcsr();

}



/* Get alignment of the TYPE. */

#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)



/*

 * Enforce that 'MEMBER' is the last field of 'TYPE'.

 *
@@ -143,8 +140,8 @@ static void __init fpu__init_system_generic(void) 
 * because that's how C aligns structs.

 */

#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \

	BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \

					   TYPE_ALIGN(TYPE)))

	BUILD_BUG_ON(sizeof(TYPE) !=         \

		     ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))



/*

 * We append the 'struct fpu' to the task_struct: