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| author | Peter Zijlstra <peterz@infradead.org> | 2021-10-26 14:01:43 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-10-28 23:25:28 +0200 |
| commit | 2f0cbb2a8e5bbf101e9de118fc0eb168111a5e1e (patch) | |
| tree | ea3435712f5e8b8a09d1a06e38da15d9b7f126bf /arch/x86/kernel/alternative.c | |
| parent | 7508500900814d14e2e085cdc4e28142721abbdf (diff) | |
| download | linux-2f0cbb2a8e5bbf101e9de118fc0eb168111a5e1e.tar.bz2 | |
x86/alternative: Handle Jcc __x86_indirect_thunk_\reg
Handle the rare cases where the compiler (clang) does an indirect
conditional tail-call using:
Jcc __x86_indirect_thunk_\reg
For the !RETPOLINE case this can be rewritten to fit the original (6
byte) instruction like:
Jncc.d8 1f
JMP *%\reg
NOP
1:
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20211026120310.296470217@infradead.org
Diffstat (limited to 'arch/x86/kernel/alternative.c')
| -rw-r--r-- | arch/x86/kernel/alternative.c | 40 |
1 files changed, 36 insertions, 4 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 5df403450359..1dea2f6c5546 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -393,7 +393,8 @@ static int emit_indirect(int op, int reg, u8 *bytes) static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) { retpoline_thunk_t *target; - int reg, i = 0; + int reg, ret, i = 0; + u8 op, cc; target = addr + insn->length + insn->immediate.value; reg = target - __x86_indirect_thunk_array; @@ -407,9 +408,36 @@ static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) return -1; - i = emit_indirect(insn->opcode.bytes[0], reg, bytes); - if (i < 0) - return i; + op = insn->opcode.bytes[0]; + + /* + * Convert: + * + * Jcc.d32 __x86_indirect_thunk_\reg + * + * into: + * + * Jncc.d8 1f + * JMP *%\reg + * NOP + * 1: + */ + /* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */ + if (op == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80) { + cc = insn->opcode.bytes[1] & 0xf; + cc ^= 1; /* invert condition */ + + bytes[i++] = 0x70 + cc; /* Jcc.d8 */ + bytes[i++] = insn->length - 2; /* sizeof(Jcc.d8) == 2 */ + + /* Continue as if: JMP.d32 __x86_indirect_thunk_\reg */ + op = JMP32_INSN_OPCODE; + } + + ret = emit_indirect(op, reg, bytes + i); + if (ret < 0) + return ret; + i += ret; for (; i < insn->length;) bytes[i++] = BYTES_NOP1; @@ -443,6 +471,10 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) case JMP32_INSN_OPCODE: break; + case 0x0f: /* escape */ + if (op2 >= 0x80 && op2 <= 0x8f) + break; + fallthrough; default: WARN_ON_ONCE(1); continue; |