linux-stable/arch/x86/include/asm/static_call.h
Peter Zijlstra e463a09af2 x86: Add straight-line-speculation mitigation
Make use of an upcoming GCC feature to mitigate
straight-line-speculation for x86:

  https://gcc.gnu.org/g:53a643f8568067d7700a9f2facc8ba39974973d3
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102952
  https://bugs.llvm.org/show_bug.cgi?id=52323

It's built tested on x86_64-allyesconfig using GCC-12 and GCC-11.

Maintenance overhead of this should be fairly low due to objtool
validation.

Size overhead of all these additional int3 instructions comes to:

     text	   data	    bss	    dec	    hex	filename
  22267751	6933356	2011368	31212475	1dc43bb	defconfig-build/vmlinux
  22804126	6933356	1470696	31208178	1dc32f2	defconfig-build/vmlinux.sls

Or roughly 2.4% additional text.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134908.140103474@infradead.org
2021-12-09 13:32:25 +01:00

48 lines
1.9 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_STATIC_CALL_H
#define _ASM_STATIC_CALL_H
#include <asm/text-patching.h>
/*
* For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
* uses the current value of the key->func pointer to do an indirect jump to
* the function. This trampoline is only used during boot, before the call
* sites get patched by static_call_update(). The name of this trampoline has
* a magical aspect: objtool uses it to find static call sites so it can create
* the .static_call_sites section.
*
* For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
* does a direct jump to the function. The direct jump gets patched by
* static_call_update().
*
* Having the trampoline in a special section forces GCC to emit a JMP.d32 when
* it does tail-call optimization on the call; since you cannot compute the
* relative displacement across sections.
*/
#define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, insns) \
asm(".pushsection .static_call.text, \"ax\" \n" \
".align 4 \n" \
".globl " STATIC_CALL_TRAMP_STR(name) " \n" \
STATIC_CALL_TRAMP_STR(name) ": \n" \
insns " \n" \
".byte 0x53, 0x43, 0x54 \n" \
".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \
".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
".popsection \n")
#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, ".byte 0xe9; .long " #func " - (. + 4)")
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; int3; nop; nop; nop")
#define ARCH_ADD_TRAMP_KEY(name) \
asm(".pushsection .static_call_tramp_key, \"a\" \n" \
".long " STATIC_CALL_TRAMP_STR(name) " - . \n" \
".long " STATIC_CALL_KEY_STR(name) " - . \n" \
".popsection \n")
#endif /* _ASM_STATIC_CALL_H */