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142 lines
3.9 KiB
142 lines
3.9 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#include <linux/stringify.h> |
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#include <linux/linkage.h> |
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#include <asm/dwarf2.h> |
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#include <asm/cpufeatures.h> |
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#include <asm/alternative.h> |
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#include <asm/export.h> |
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#include <asm/nospec-branch.h> |
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#include <asm/unwind_hints.h> |
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#include <asm/frame.h> |
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.section .text.__x86.indirect_thunk |
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.macro RETPOLINE reg |
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ANNOTATE_INTRA_FUNCTION_CALL |
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call .Ldo_rop_\@ |
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.Lspec_trap_\@: |
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UNWIND_HINT_EMPTY |
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pause |
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lfence |
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jmp .Lspec_trap_\@ |
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.Ldo_rop_\@: |
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mov %\reg, (%_ASM_SP) |
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UNWIND_HINT_FUNC |
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RET |
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.endm |
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.macro THUNK reg |
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.align RETPOLINE_THUNK_SIZE |
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SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) |
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UNWIND_HINT_EMPTY |
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ANNOTATE_NOENDBR |
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ALTERNATIVE_2 __stringify(RETPOLINE \reg), \ |
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__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \ |
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__stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE) |
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.endm |
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/* |
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* Despite being an assembler file we can't just use .irp here |
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* because __KSYM_DEPS__ only uses the C preprocessor and would |
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* only see one instance of "__x86_indirect_thunk_\reg" rather |
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* than one per register with the correct names. So we do it |
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* the simple and nasty way... |
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* |
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* Worse, you can only have a single EXPORT_SYMBOL per line, |
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* and CPP can't insert newlines, so we have to repeat everything |
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* at least twice. |
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*/ |
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#define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym) |
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#define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg) |
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.align RETPOLINE_THUNK_SIZE |
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SYM_CODE_START(__x86_indirect_thunk_array) |
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#define GEN(reg) THUNK reg |
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#include <asm/GEN-for-each-reg.h> |
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#undef GEN |
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.align RETPOLINE_THUNK_SIZE |
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SYM_CODE_END(__x86_indirect_thunk_array) |
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#define GEN(reg) EXPORT_THUNK(reg) |
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#include <asm/GEN-for-each-reg.h> |
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#undef GEN |
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/* |
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* This function name is magical and is used by -mfunction-return=thunk-extern |
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* for the compiler to generate JMPs to it. |
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*/ |
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#ifdef CONFIG_RETHUNK |
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.section .text.__x86.return_thunk |
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/* |
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* Safety details here pertain to the AMD Zen{1,2} microarchitecture: |
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* 1) The RET at __x86_return_thunk must be on a 64 byte boundary, for |
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* alignment within the BTB. |
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* 2) The instruction at zen_untrain_ret must contain, and not |
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* end with, the 0xc3 byte of the RET. |
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* 3) STIBP must be enabled, or SMT disabled, to prevent the sibling thread |
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* from re-poisioning the BTB prediction. |
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*/ |
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.align 64 |
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.skip 63, 0xcc |
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SYM_FUNC_START_NOALIGN(zen_untrain_ret); |
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/* |
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* As executed from zen_untrain_ret, this is: |
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* |
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* TEST $0xcc, %bl |
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* LFENCE |
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* JMP __x86_return_thunk |
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* |
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* Executing the TEST instruction has a side effect of evicting any BTB |
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* prediction (potentially attacker controlled) attached to the RET, as |
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* __x86_return_thunk + 1 isn't an instruction boundary at the moment. |
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*/ |
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.byte 0xf6 |
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/* |
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* As executed from __x86_return_thunk, this is a plain RET. |
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* |
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* As part of the TEST above, RET is the ModRM byte, and INT3 the imm8. |
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* |
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* We subsequently jump backwards and architecturally execute the RET. |
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* This creates a correct BTB prediction (type=ret), but in the |
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* meantime we suffer Straight Line Speculation (because the type was |
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* no branch) which is halted by the INT3. |
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* |
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* With SMT enabled and STIBP active, a sibling thread cannot poison |
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* RET's prediction to a type of its choice, but can evict the |
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* prediction due to competitive sharing. If the prediction is |
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* evicted, __x86_return_thunk will suffer Straight Line Speculation |
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* which will be contained safely by the INT3. |
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*/ |
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SYM_INNER_LABEL(__x86_return_thunk, SYM_L_GLOBAL) |
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ret |
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int3 |
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SYM_CODE_END(__x86_return_thunk) |
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/* |
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* Ensure the TEST decoding / BTB invalidation is complete. |
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*/ |
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lfence |
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/* |
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* Jump back and execute the RET in the middle of the TEST instruction. |
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* INT3 is for SLS protection. |
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*/ |
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jmp __x86_return_thunk |
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int3 |
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SYM_FUNC_END(zen_untrain_ret) |
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__EXPORT_THUNK(zen_untrain_ret) |
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EXPORT_SYMBOL(__x86_return_thunk) |
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#endif /* CONFIG_RETHUNK */
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