x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n

If a kernel is built with CONFIG_RETPOLINE=n, but the user still wants to mitigate Spectre v2 using IBRS or eIBRS, the RSB filling will be silently disabled. There's nothing retpoline-specific about RSB buffer filling. Remove the CONFIG_RETPOLINE guards around it.

Josh Poimboeuf committed 4 years ago

Commit b2620fa1 parent d7caac93 files · +0 −6Browse files

Unified · Split

3 files

arch/x86/entry/entry_32.S +0 −2
arch/x86/entry/entry_64.S +0 −2
arch/x86/include/asm/nospec-branch.h +0 −2

arch/x86/entry/entry_32.S+0−2

@@ -698,7 +698,6 @@ SYM_CODE_START(__switch_to_asm) · 697 unmodified lines
698	698	movl %ebx, PER_CPU_VAR(__stack_chk_guard)
699	699	#endif
700	700
701		−#ifdef CONFIG_RETPOLINE
702	701	/*
703	702	* When switching from a shallower to a deeper call stack
704	703	* the RSB may either underflow or use entries populated
@@ -707,7 +706,6 @@ SYM_CODE_START(__switch_to_asm) · 2 unmodified lines
707	706	* speculative execution to prevent attack.
708	707	*/
709	708	FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
710		−#endif
711	709
712	710	/* Restore flags or the incoming task to restore AC state. */
713	711	popfl

arch/x86/entry/entry_64.S+0−2

@@ -255,7 +255,6 @@ SYM_FUNC_START(__switch_to_asm) · 254 unmodified lines
255	255	movq %rbx, PER_CPU_VAR(fixed_percpu_data) + stack_canary_offset
256	256	#endif
257	257
258		−#ifdef CONFIG_RETPOLINE
259	258	/*
260	259	* When switching from a shallower to a deeper call stack
261	260	* the RSB may either underflow or use entries populated
@@ -264,7 +263,6 @@ SYM_FUNC_START(__switch_to_asm) · 2 unmodified lines
264	263	* speculative execution to prevent attack.
265	264	*/
266	265	FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
267		−#endif
268	266
269	267	/* restore callee-saved registers */
270	268	popq %r15

arch/x86/include/asm/nospec-branch.h+0−2

@@ -122,11 +122,9 @@ · 121 unmodified lines
122	122	* monstrosity above, manually.
123	123	*/
124	124	.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
125		−#ifdef CONFIG_RETPOLINE
126	125	ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr
127	126	__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)
128	127	.Lskip_rsb_\@:
129		−#endif
130	128	.endm
131	129
132	130	/*