Commit e7c25c44 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov (AMD)
Browse files

x86/cpu: Cleanup the untrain mess 



Since there can only be one active return_thunk, there only needs be
one (matching) untrain_ret. It fundamentally doesn't make sense to
allow multiple untrain_ret at the same time.

Fold all the 3 different untrain methods into a single (temporary)
helper stub.

Fixes: fb3bd914 ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121149.042774962@infradead.org
parent 42be649d

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

+5 −14
Original line number Diff line number Diff line
@@ -272,9 +272,9 @@ 
.endm



#ifdef CONFIG_CPU_UNRET_ENTRY

#define CALL_ZEN_UNTRAIN_RET	"call retbleed_untrain_ret"

#define CALL_UNTRAIN_RET	"call entry_untrain_ret"

#else

#define CALL_ZEN_UNTRAIN_RET	""

#define CALL_UNTRAIN_RET	""

#endif



/*
@@ -293,15 +293,10 @@ 
	defined(CONFIG_CALL_DEPTH_TRACKING) || defined(CONFIG_CPU_SRSO)

	VALIDATE_UNRET_END

	ALTERNATIVE_3 "",						\

		      CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET,		\

		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\

		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB,	\

		      __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH

#endif



#ifdef CONFIG_CPU_SRSO

	ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \

			  "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS

#endif

.endm



.macro UNTRAIN_RET_FROM_CALL
@@ -309,15 +304,10 @@ 
	defined(CONFIG_CALL_DEPTH_TRACKING)

	VALIDATE_UNRET_END

	ALTERNATIVE_3 "",						\

		      CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET,		\

		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\

		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB,	\

		      __stringify(RESET_CALL_DEPTH_FROM_CALL), X86_FEATURE_CALL_DEPTH

#endif



#ifdef CONFIG_CPU_SRSO

	ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \

			  "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS

#endif

.endm
@@ -355,6 +345,7 @@ extern void retbleed_untrain_ret(void); 
extern void srso_untrain_ret(void);

extern void srso_alias_untrain_ret(void);



extern void entry_untrain_ret(void);

extern void entry_ibpb(void);



extern void (*x86_return_thunk)(void);

arch/x86/kernel/cpu/bugs.c

+1 −0
Original line number Diff line number Diff line
@@ -2460,6 +2460,7 @@ static void __init srso_select_mitigation(void) 
			 * like ftrace, static_call, etc.

			 */

			setup_force_cpu_cap(X86_FEATURE_RETHUNK);

			setup_force_cpu_cap(X86_FEATURE_UNRET);



			if (boot_cpu_data.x86 == 0x19) {

				setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);

arch/x86/lib/retpoline.S

+7 −0
Original line number Diff line number Diff line
@@ -289,6 +289,13 @@ SYM_CODE_START(srso_return_thunk) 
	ud2

SYM_CODE_END(srso_return_thunk)



SYM_FUNC_START(entry_untrain_ret)

	ALTERNATIVE_2 "jmp retbleed_untrain_ret", \

		      "jmp srso_untrain_ret", X86_FEATURE_SRSO, \

		      "jmp srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS

SYM_FUNC_END(entry_untrain_ret)

__EXPORT_THUNK(entry_untrain_ret)



SYM_CODE_START(__x86_return_thunk)

	UNWIND_HINT_FUNC

	ANNOTATE_NOENDBR