| /* SPDX-License-Identifier: GPL-2.0 */ |
| |
| #include <linux/export.h> |
| #include <linux/stringify.h> |
| #include <linux/linkage.h> |
| #include <asm/dwarf2.h> |
| #include <asm/cpufeatures.h> |
| #include <asm/alternative.h> |
| #include <asm/asm-offsets.h> |
| #include <asm/nospec-branch.h> |
| #include <asm/unwind_hints.h> |
| #include <asm/percpu.h> |
| #include <asm/frame.h> |
| #include <asm/nops.h> |
| |
| .section .text..__x86.indirect_thunk |
| |
| |
| .macro POLINE reg |
| ANNOTATE_INTRA_FUNCTION_CALL |
| call .Ldo_rop_\@ |
| int3 |
| .Ldo_rop_\@: |
| mov %\reg, (%_ASM_SP) |
| UNWIND_HINT_FUNC |
| .endm |
| |
| .macro RETPOLINE reg |
| POLINE \reg |
| RET |
| .endm |
| |
| .macro THUNK reg |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) |
| UNWIND_HINT_UNDEFINED |
| ANNOTATE_NOENDBR |
| |
| ALTERNATIVE_2 __stringify(RETPOLINE \reg), \ |
| __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \ |
| __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE) |
| |
| .endm |
| |
| /* |
| * Despite being an assembler file we can't just use .irp here |
| * because __KSYM_DEPS__ only uses the C preprocessor and would |
| * only see one instance of "__x86_indirect_thunk_\reg" rather |
| * than one per register with the correct names. So we do it |
| * the simple and nasty way... |
| * |
| * Worse, you can only have a single EXPORT_SYMBOL per line, |
| * and CPP can't insert newlines, so we have to repeat everything |
| * at least twice. |
| */ |
| |
| #define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym) |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_START(__x86_indirect_thunk_array) |
| |
| #define GEN(reg) THUNK reg |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_END(__x86_indirect_thunk_array) |
| |
| #define GEN(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg) |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| |
| #ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING |
| .macro CALL_THUNK reg |
| .align RETPOLINE_THUNK_SIZE |
| |
| SYM_INNER_LABEL(__x86_indirect_call_thunk_\reg, SYM_L_GLOBAL) |
| UNWIND_HINT_UNDEFINED |
| ANNOTATE_NOENDBR |
| |
| CALL_DEPTH_ACCOUNT |
| POLINE \reg |
| ANNOTATE_UNRET_SAFE |
| ret |
| int3 |
| .endm |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_START(__x86_indirect_call_thunk_array) |
| |
| #define GEN(reg) CALL_THUNK reg |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_END(__x86_indirect_call_thunk_array) |
| |
| #define GEN(reg) __EXPORT_THUNK(__x86_indirect_call_thunk_ ## reg) |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| |
| .macro JUMP_THUNK reg |
| .align RETPOLINE_THUNK_SIZE |
| |
| SYM_INNER_LABEL(__x86_indirect_jump_thunk_\reg, SYM_L_GLOBAL) |
| UNWIND_HINT_UNDEFINED |
| ANNOTATE_NOENDBR |
| POLINE \reg |
| ANNOTATE_UNRET_SAFE |
| ret |
| int3 |
| .endm |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_START(__x86_indirect_jump_thunk_array) |
| |
| #define GEN(reg) JUMP_THUNK reg |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| |
| .align RETPOLINE_THUNK_SIZE |
| SYM_CODE_END(__x86_indirect_jump_thunk_array) |
| |
| #define GEN(reg) __EXPORT_THUNK(__x86_indirect_jump_thunk_ ## reg) |
| #include <asm/GEN-for-each-reg.h> |
| #undef GEN |
| #endif |
| |
| #ifdef CONFIG_MITIGATION_RETHUNK |
| |
| /* |
| * Be careful here: that label cannot really be removed because in |
| * some configurations and toolchains, the JMP __x86_return_thunk the |
| * compiler issues is either a short one or the compiler doesn't use |
| * relocations for same-section JMPs and that breaks the returns |
| * detection logic in apply_returns() and in objtool. |
| */ |
| .section .text..__x86.return_thunk |
| |
| #ifdef CONFIG_MITIGATION_SRSO |
| |
| /* |
| * srso_alias_untrain_ret() and srso_alias_safe_ret() are placed at |
| * special addresses: |
| * |
| * - srso_alias_untrain_ret() is 2M aligned |
| * - srso_alias_safe_ret() is also in the same 2M page but bits 2, 8, 14 |
| * and 20 in its virtual address are set (while those bits in the |
| * srso_alias_untrain_ret() function are cleared). |
| * |
| * This guarantees that those two addresses will alias in the branch |
| * target buffer of Zen3/4 generations, leading to any potential |
| * poisoned entries at that BTB slot to get evicted. |
| * |
| * As a result, srso_alias_safe_ret() becomes a safe return. |
| */ |
| .pushsection .text..__x86.rethunk_untrain |
| SYM_CODE_START_NOALIGN(srso_alias_untrain_ret) |
| UNWIND_HINT_FUNC |
| ANNOTATE_NOENDBR |
| ASM_NOP2 |
| lfence |
| jmp srso_alias_return_thunk |
| SYM_FUNC_END(srso_alias_untrain_ret) |
| __EXPORT_THUNK(srso_alias_untrain_ret) |
| .popsection |
| |
| .pushsection .text..__x86.rethunk_safe |
| SYM_CODE_START_NOALIGN(srso_alias_safe_ret) |
| lea 8(%_ASM_SP), %_ASM_SP |
| UNWIND_HINT_FUNC |
| ANNOTATE_UNRET_SAFE |
| ret |
| int3 |
| SYM_FUNC_END(srso_alias_safe_ret) |
| |
| SYM_CODE_START_NOALIGN(srso_alias_return_thunk) |
| UNWIND_HINT_FUNC |
| ANNOTATE_NOENDBR |
| call srso_alias_safe_ret |
| ud2 |
| SYM_CODE_END(srso_alias_return_thunk) |
| .popsection |
| |
| /* |
| * SRSO untraining sequence for Zen1/2, similar to retbleed_untrain_ret() |
| * above. On kernel entry, srso_untrain_ret() is executed which is a |
| * |
| * movabs $0xccccc30824648d48,%rax |
| * |
| * and when the return thunk executes the inner label srso_safe_ret() |
| * later, it is a stack manipulation and a RET which is mispredicted and |
| * thus a "safe" one to use. |
| */ |
| .align 64 |
| .skip 64 - (srso_safe_ret - srso_untrain_ret), 0xcc |
| SYM_CODE_START_LOCAL_NOALIGN(srso_untrain_ret) |
| 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 |
| SYM_CODE_END(srso_safe_ret) |
| SYM_FUNC_END(srso_untrain_ret) |
| |
| SYM_CODE_START(srso_return_thunk) |
| UNWIND_HINT_FUNC |
| ANNOTATE_NOENDBR |
| call srso_safe_ret |
| ud2 |
| SYM_CODE_END(srso_return_thunk) |
| |
| #define JMP_SRSO_UNTRAIN_RET "jmp srso_untrain_ret" |
| #else /* !CONFIG_MITIGATION_SRSO */ |
| /* Dummy for the alternative in CALL_UNTRAIN_RET. */ |
| SYM_CODE_START(srso_alias_untrain_ret) |
| ANNOTATE_UNRET_SAFE |
| ANNOTATE_NOENDBR |
| ret |
| int3 |
| SYM_FUNC_END(srso_alias_untrain_ret) |
| __EXPORT_THUNK(srso_alias_untrain_ret) |
| #define JMP_SRSO_UNTRAIN_RET "ud2" |
| #endif /* CONFIG_MITIGATION_SRSO */ |
| |
| #ifdef CONFIG_MITIGATION_UNRET_ENTRY |
| |
| /* |
| * Some generic notes on the untraining sequences: |
| * |
| * They are interchangeable when it comes to flushing potentially wrong |
| * RET predictions from the BTB. |
| * |
| * The SRSO Zen1/2 (MOVABS) untraining sequence is longer than the |
| * Retbleed sequence because the return sequence done there |
| * (srso_safe_ret()) is longer and the return sequence must fully nest |
| * (end before) the untraining sequence. Therefore, the untraining |
| * sequence must fully overlap the return sequence. |
| * |
| * Regarding alignment - the instructions which need to be untrained, |
| * must all start at a cacheline boundary for Zen1/2 generations. That |
| * is, instruction sequences starting at srso_safe_ret() and |
| * the respective instruction sequences at retbleed_return_thunk() |
| * must start at a cacheline boundary. |
| */ |
| |
| /* |
| * Safety details here pertain to the AMD Zen{1,2} microarchitecture: |
| * 1) The RET at retbleed_return_thunk must be on a 64 byte boundary, for |
| * alignment within the BTB. |
| * 2) The instruction at retbleed_untrain_ret must contain, and not |
| * end with, the 0xc3 byte of the RET. |
| * 3) STIBP must be enabled, or SMT disabled, to prevent the sibling thread |
| * from re-poisioning the BTB prediction. |
| */ |
| .align 64 |
| .skip 64 - (retbleed_return_thunk - retbleed_untrain_ret), 0xcc |
| SYM_CODE_START_LOCAL_NOALIGN(retbleed_untrain_ret) |
| ANNOTATE_NOENDBR |
| /* |
| * As executed from retbleed_untrain_ret, this is: |
| * |
| * TEST $0xcc, %bl |
| * LFENCE |
| * JMP retbleed_return_thunk |
| * |
| * Executing the TEST instruction has a side effect of evicting any BTB |
| * prediction (potentially attacker controlled) attached to the RET, as |
| * retbleed_return_thunk + 1 isn't an instruction boundary at the moment. |
| */ |
| .byte 0xf6 |
| |
| /* |
| * As executed from retbleed_return_thunk, this is a plain RET. |
| * |
| * As part of the TEST above, RET is the ModRM byte, and INT3 the imm8. |
| * |
| * We subsequently jump backwards and architecturally execute the RET. |
| * This creates a correct BTB prediction (type=ret), but in the |
| * meantime we suffer Straight Line Speculation (because the type was |
| * no branch) which is halted by the INT3. |
| * |
| * 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, retbleed_return_thunk will suffer Straight Line Speculation |
| * which will be contained safely by the INT3. |
| */ |
| SYM_INNER_LABEL(retbleed_return_thunk, SYM_L_GLOBAL) |
| ret |
| int3 |
| SYM_CODE_END(retbleed_return_thunk) |
| |
| /* |
| * Ensure the TEST decoding / BTB invalidation is complete. |
| */ |
| lfence |
| |
| /* |
| * Jump back and execute the RET in the middle of the TEST instruction. |
| * INT3 is for SLS protection. |
| */ |
| jmp retbleed_return_thunk |
| int3 |
| SYM_FUNC_END(retbleed_untrain_ret) |
| |
| #define JMP_RETBLEED_UNTRAIN_RET "jmp retbleed_untrain_ret" |
| #else /* !CONFIG_MITIGATION_UNRET_ENTRY */ |
| #define JMP_RETBLEED_UNTRAIN_RET "ud2" |
| #endif /* CONFIG_MITIGATION_UNRET_ENTRY */ |
| |
| #if defined(CONFIG_MITIGATION_UNRET_ENTRY) || defined(CONFIG_MITIGATION_SRSO) |
| |
| SYM_FUNC_START(entry_untrain_ret) |
| ALTERNATIVE JMP_RETBLEED_UNTRAIN_RET, JMP_SRSO_UNTRAIN_RET, X86_FEATURE_SRSO |
| SYM_FUNC_END(entry_untrain_ret) |
| __EXPORT_THUNK(entry_untrain_ret) |
| |
| #endif /* CONFIG_MITIGATION_UNRET_ENTRY || CONFIG_MITIGATION_SRSO */ |
| |
| #ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING |
| |
| .align 64 |
| SYM_FUNC_START(call_depth_return_thunk) |
| ANNOTATE_NOENDBR |
| /* |
| * Keep the hotpath in a 16byte I-fetch for the non-debug |
| * case. |
| */ |
| CALL_THUNKS_DEBUG_INC_RETS |
| shlq $5, PER_CPU_VAR(pcpu_hot + X86_call_depth) |
| jz 1f |
| ANNOTATE_UNRET_SAFE |
| ret |
| int3 |
| 1: |
| CALL_THUNKS_DEBUG_INC_STUFFS |
| .rept 16 |
| ANNOTATE_INTRA_FUNCTION_CALL |
| call 2f |
| int3 |
| 2: |
| .endr |
| add $(8*16), %rsp |
| |
| CREDIT_CALL_DEPTH |
| |
| ANNOTATE_UNRET_SAFE |
| ret |
| int3 |
| SYM_FUNC_END(call_depth_return_thunk) |
| |
| #endif /* CONFIG_MITIGATION_CALL_DEPTH_TRACKING */ |
| |
| /* |
| * This function name is magical and is used by -mfunction-return=thunk-extern |
| * for the compiler to generate JMPs to it. |
| * |
| * This code is only used during kernel boot or module init. All |
| * 'JMP __x86_return_thunk' sites are changed to something else by |
| * apply_returns(). |
| * |
| * The ALTERNATIVE below adds a really loud warning to catch the case |
| * where the insufficient default return thunk ends up getting used for |
| * whatever reason like miscompilation or failure of |
| * objtool/alternatives/etc to patch all the return sites. |
| */ |
| SYM_CODE_START(__x86_return_thunk) |
| UNWIND_HINT_FUNC |
| ANNOTATE_NOENDBR |
| ALTERNATIVE __stringify(ANNOTATE_UNRET_SAFE; ret), \ |
| "jmp warn_thunk_thunk", X86_FEATURE_ALWAYS |
| int3 |
| SYM_CODE_END(__x86_return_thunk) |
| EXPORT_SYMBOL(__x86_return_thunk) |
| |
| #endif /* CONFIG_MITIGATION_RETHUNK */ |
