Commit 09d09531 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86,nospec: Simplify {JMP,CALL}_NOSPEC 



Have {JMP,CALL}_NOSPEC generate the same code GCC does for indirect
calls and rely on the objtool retpoline patching infrastructure.

There's no reason these should be alternatives while the vast bulk of
compiler generated retpolines are not.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent ff699273

arch/x86/include/asm/nospec-branch.h

+18 −6
Original line number Diff line number Diff line
@@ -93,6 +93,19 @@ 
#endif

.endm



/*

 * Equivalent to -mindirect-branch-cs-prefix; emit the 5 byte jmp/call

 * to the retpoline thunk with a CS prefix when the register requires

 * a RAX prefix byte to encode. Also see apply_retpolines().

 */

.macro __CS_PREFIX reg:req

	.irp rs,r8,r9,r10,r11,r12,r13,r14,r15

	.ifc \reg,\rs

	.byte 0x2e

	.endif

	.endr

.endm



/*

 * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple

 * indirect jmp/call which may be susceptible to the Spectre variant 2
@@ -100,19 +113,18 @@ 
 */

.macro JMP_NOSPEC reg:req

#ifdef CONFIG_RETPOLINE

	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \

		      __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \

		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE

	__CS_PREFIX \reg

	jmp	__x86_indirect_thunk_\reg

#else

	jmp	*%\reg

	int3

#endif

.endm



.macro CALL_NOSPEC reg:req

#ifdef CONFIG_RETPOLINE

	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \

		      __stringify(call __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \

		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_LFENCE

	__CS_PREFIX \reg

	call	__x86_indirect_thunk_\reg

#else

	call	*%\reg

#endif