Messages in this thread Patch in this message | | | Date | Wed, 09 Aug 2023 09:12:35 +0200 | From | Peter Zijlstra <> | Subject | [RFC][PATCH 17/17] x86/cpu: Use fancy alternatives to get rid of entry_untrain_ret() |
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Use the new nested alternatives to create what is effectively ALTERNATIVE_5 and merge the dummy entry_untrain_ret stub into UNTRAIN_RET properly.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/include/asm/nospec-branch.h | 33 ++++++++++++++++++--------------- arch/x86/lib/retpoline.S | 7 ------- 2 files changed, 18 insertions(+), 22 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -271,11 +271,15 @@ .endm #ifdef CONFIG_CPU_UNRET_ENTRY -#define CALL_UNTRAIN_RET "call entry_untrain_ret" +#define ALT_UNRET(old) \ + __ALTERNATIVE(__ALTERNATIVE(__ALTERNATIVE(old, call zen_untrain_ret, X86_FEATURE_UNRET), \ + call srso_untrain_ret, X86_FEATURE_SRSO), \ + call srso_alias_untrain_ret, X86_FEATURE_SRSO_ALIAS) #else -#define CALL_UNTRAIN_RET "" +#define ALT_UNRET(old) old #endif + /* * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the * return thunk isn't mapped into the userspace tables (then again, AMD @@ -290,30 +294,30 @@ .macro UNTRAIN_RET #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CALL_DEPTH_TRACKING) VALIDATE_UNRET_END - ALTERNATIVE_3 "", \ - CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \ - "call entry_ibpb", X86_FEATURE_ENTRY_IBPB, \ - __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH + + __ALTERNATIVE(__ALTERNATIVE(ALT_UNRET(;), + call entry_ibpb, X86_FEATURE_ENTRY_IBPB), + RESET_CALL_DEPTH, X86_FEATURE_CALL_DEPTH) #endif .endm .macro UNTRAIN_RET_VM #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CALL_DEPTH_TRACKING) VALIDATE_UNRET_END - ALTERNATIVE_3 "", \ - CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \ - "call entry_ibpb", X86_FEATURE_IBPB_ON_VMEXIT, \ - __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH + + __ALTERNATIVE(__ALTERNATIVE(ALT_UNRET(;), + call entry_ibpb, X86_FEATURE_IBPB_ON_VMEXIT), + RESET_CALL_DEPTH, X86_FEATURE_CALL_DEPTH) #endif .endm .macro UNTRAIN_RET_FROM_CALL #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CALL_DEPTH_TRACKING) VALIDATE_UNRET_END - ALTERNATIVE_3 "", \ - CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \ - "call entry_ibpb", X86_FEATURE_ENTRY_IBPB, \ - __stringify(RESET_CALL_DEPTH_FROM_CALL), X86_FEATURE_CALL_DEPTH + + __ALTERNATIVE(__ALTERNATIVE(ALT_UNRET(;), + call entry_ibpb, X86_FEATURE_ENTRY_IBPB), + RESET_CALL_DEPTH_FROM_CALL, X86_FEATURE_CALL_DEPTH) #endif .endm @@ -348,7 +352,6 @@ extern void zen_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); --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -263,13 +263,6 @@ SYM_CODE_END(srso_safe_ret) SYM_FUNC_END(srso_untrain_ret) __EXPORT_THUNK(srso_untrain_ret) -SYM_FUNC_START(entry_untrain_ret) - ALTERNATIVE_2 "jmp zen_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) - /* * Both these do an unbalanced CALL to mess up the RSB, terminate with UD2 * to indicate noreturn.
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