diff options
Diffstat (limited to 'arch/x86/lib/retpoline.S')
| -rw-r--r-- | arch/x86/lib/retpoline.S | 58 |
1 files changed, 42 insertions, 16 deletions
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index a478eb5bbf62..7df8582fb64e 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -151,22 +151,27 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array) .section .text..__x86.rethunk_untrain SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE) + UNWIND_HINT_FUNC ANNOTATE_NOENDBR ASM_NOP2 lfence - jmp __x86_return_thunk + jmp srso_alias_return_thunk SYM_FUNC_END(srso_untrain_ret_alias) __EXPORT_THUNK(srso_untrain_ret_alias) .section .text..__x86.rethunk_safe +#else +/* dummy definition for alternatives */ +SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE) + ANNOTATE_UNRET_SAFE + ret + int3 +SYM_FUNC_END(srso_untrain_ret_alias) #endif -/* Needs a definition for the __x86_return_thunk alternative below. */ SYM_START(srso_safe_ret_alias, SYM_L_GLOBAL, SYM_A_NONE) -#ifdef CONFIG_CPU_SRSO lea 8(%_ASM_SP), %_ASM_SP UNWIND_HINT_FUNC -#endif ANNOTATE_UNRET_SAFE ret int3 @@ -174,9 +179,16 @@ SYM_FUNC_END(srso_safe_ret_alias) .section .text..__x86.return_thunk +SYM_CODE_START(srso_alias_return_thunk) + UNWIND_HINT_FUNC + ANNOTATE_NOENDBR + call srso_safe_ret_alias + ud2 +SYM_CODE_END(srso_alias_return_thunk) + /* * Safety details here pertain to the AMD Zen{1,2} microarchitecture: - * 1) The RET at __x86_return_thunk must be on a 64 byte boundary, for + * 1) The RET at zen_return_thunk must be on a 64 byte boundary, for * alignment within the BTB. * 2) The instruction at zen_untrain_ret must contain, and not * end with, the 0xc3 byte of the RET. @@ -184,7 +196,7 @@ SYM_FUNC_END(srso_safe_ret_alias) * from re-poisioning the BTB prediction. */ .align 64 - .skip 64 - (__ret - zen_untrain_ret), 0xcc + .skip 64 - (zen_return_thunk - zen_untrain_ret), 0xcc SYM_START(zen_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE) ANNOTATE_NOENDBR /* @@ -192,16 +204,16 @@ SYM_START(zen_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE) * * TEST $0xcc, %bl * LFENCE - * JMP __x86_return_thunk + * JMP zen_return_thunk * * Executing the TEST instruction has a side effect of evicting any BTB * prediction (potentially attacker controlled) attached to the RET, as - * __x86_return_thunk + 1 isn't an instruction boundary at the moment. + * zen_return_thunk + 1 isn't an instruction boundary at the moment. */ .byte 0xf6 /* - * As executed from __x86_return_thunk, this is a plain RET. + * As executed from zen_return_thunk, this is a plain RET. * * As part of the TEST above, RET is the ModRM byte, and INT3 the imm8. * @@ -213,13 +225,13 @@ SYM_START(zen_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE) * With SMT enabled and STIBP active, a sibling thread cannot poison * RET's prediction to a type of its choice, but can evict the * prediction due to competitive sharing. If the prediction is - * evicted, __x86_return_thunk will suffer Straight Line Speculation + * evicted, zen_return_thunk will suffer Straight Line Speculation * which will be contained safely by the INT3. */ -SYM_INNER_LABEL(__ret, SYM_L_GLOBAL) +SYM_INNER_LABEL(zen_return_thunk, SYM_L_GLOBAL) ret int3 -SYM_CODE_END(__ret) +SYM_CODE_END(zen_return_thunk) /* * Ensure the TEST decoding / BTB invalidation is complete. @@ -230,7 +242,7 @@ SYM_CODE_END(__ret) * Jump back and execute the RET in the middle of the TEST instruction. * INT3 is for SLS protection. */ - jmp __ret + jmp zen_return_thunk int3 SYM_FUNC_END(zen_untrain_ret) __EXPORT_THUNK(zen_untrain_ret) @@ -251,11 +263,18 @@ SYM_START(srso_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE) ANNOTATE_NOENDBR .byte 0x48, 0xb8 +/* + * This forces the function return instruction to speculate into a trap + * (UD2 in srso_return_thunk() below). This RET will then mispredict + * and execution will continue at the return site read from the top of + * the stack. + */ SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL) lea 8(%_ASM_SP), %_ASM_SP ret int3 int3 + /* end of movabs */ lfence call srso_safe_ret ud2 @@ -263,12 +282,19 @@ SYM_CODE_END(srso_safe_ret) SYM_FUNC_END(srso_untrain_ret) __EXPORT_THUNK(srso_untrain_ret) -SYM_CODE_START(__x86_return_thunk) +SYM_CODE_START(srso_return_thunk) UNWIND_HINT_FUNC ANNOTATE_NOENDBR - ALTERNATIVE_2 "jmp __ret", "call srso_safe_ret", X86_FEATURE_SRSO, \ - "call srso_safe_ret_alias", X86_FEATURE_SRSO_ALIAS + call srso_safe_ret ud2 +SYM_CODE_END(srso_return_thunk) + +SYM_CODE_START(__x86_return_thunk) + UNWIND_HINT_FUNC + ANNOTATE_NOENDBR + ANNOTATE_UNRET_SAFE + ret + int3 SYM_CODE_END(__x86_return_thunk) EXPORT_SYMBOL(__x86_return_thunk) |