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x86/alternatives: Teach text_poke_bp() to patch Jcc.d32 instructions
In order to re-write Jcc.d32 instructions text_poke_bp() needs to be taught about them. The biggest hurdle is that the whole machinery is currently made for 5 byte instructions and extending this would grow struct text_poke_loc which is currently a nice 16 bytes and used in an array. However, since text_poke_loc contains a full copy of the (s32) displacement, it is possible to map the Jcc.d32 2 byte opcodes to Jcc.d8 1 byte opcode for the int3 emulation. This then leaves the replacement bytes; fudge that by only storing the last 5 bytes and adding the rule that 'length == 6' instruction will be prefixed with a 0x0f byte. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Link: https://lore.kernel.org/r/20230123210607.115718513@infradead.org
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db7adcfd1c
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1 changed files with 47 additions and 15 deletions
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@ -338,6 +338,12 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
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}
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}
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static inline bool is_jcc32(struct insn *insn)
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{
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/* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */
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return insn->opcode.bytes[0] == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80;
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}
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#if defined(CONFIG_RETPOLINE) && defined(CONFIG_OBJTOOL)
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/*
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@ -376,12 +382,6 @@ static int emit_indirect(int op, int reg, u8 *bytes)
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return i;
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}
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static inline bool is_jcc32(struct insn *insn)
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{
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/* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */
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return insn->opcode.bytes[0] == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80;
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}
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static int emit_call_track_retpoline(void *addr, struct insn *insn, int reg, u8 *bytes)
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{
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u8 op = insn->opcode.bytes[0];
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@ -1770,6 +1770,11 @@ void text_poke_sync(void)
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on_each_cpu(do_sync_core, NULL, 1);
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}
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/*
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* NOTE: crazy scheme to allow patching Jcc.d32 but not increase the size of
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* this thing. When len == 6 everything is prefixed with 0x0f and we map
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* opcode to Jcc.d8, using len to distinguish.
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*/
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struct text_poke_loc {
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/* addr := _stext + rel_addr */
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s32 rel_addr;
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@ -1891,6 +1896,10 @@ noinstr int poke_int3_handler(struct pt_regs *regs)
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int3_emulate_jmp(regs, (long)ip + tp->disp);
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break;
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case 0x70 ... 0x7f: /* Jcc */
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int3_emulate_jcc(regs, tp->opcode & 0xf, (long)ip, tp->disp);
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break;
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default:
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BUG();
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}
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@ -1964,16 +1973,26 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries
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* Second step: update all but the first byte of the patched range.
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*/
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for (do_sync = 0, i = 0; i < nr_entries; i++) {
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u8 old[POKE_MAX_OPCODE_SIZE] = { tp[i].old, };
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u8 old[POKE_MAX_OPCODE_SIZE+1] = { tp[i].old, };
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u8 _new[POKE_MAX_OPCODE_SIZE+1];
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const u8 *new = tp[i].text;
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int len = tp[i].len;
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if (len - INT3_INSN_SIZE > 0) {
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memcpy(old + INT3_INSN_SIZE,
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text_poke_addr(&tp[i]) + INT3_INSN_SIZE,
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len - INT3_INSN_SIZE);
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if (len == 6) {
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_new[0] = 0x0f;
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memcpy(_new + 1, new, 5);
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new = _new;
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}
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text_poke(text_poke_addr(&tp[i]) + INT3_INSN_SIZE,
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(const char *)tp[i].text + INT3_INSN_SIZE,
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new + INT3_INSN_SIZE,
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len - INT3_INSN_SIZE);
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do_sync++;
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}
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@ -2001,8 +2020,7 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries
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* The old instruction is recorded so that the event can be
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* processed forwards or backwards.
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*/
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perf_event_text_poke(text_poke_addr(&tp[i]), old, len,
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tp[i].text, len);
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perf_event_text_poke(text_poke_addr(&tp[i]), old, len, new, len);
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}
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if (do_sync) {
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@ -2019,10 +2037,15 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries
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* replacing opcode.
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*/
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for (do_sync = 0, i = 0; i < nr_entries; i++) {
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if (tp[i].text[0] == INT3_INSN_OPCODE)
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u8 byte = tp[i].text[0];
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if (tp[i].len == 6)
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byte = 0x0f;
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if (byte == INT3_INSN_OPCODE)
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continue;
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text_poke(text_poke_addr(&tp[i]), tp[i].text, INT3_INSN_SIZE);
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text_poke(text_poke_addr(&tp[i]), &byte, INT3_INSN_SIZE);
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do_sync++;
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}
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@ -2040,9 +2063,11 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
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const void *opcode, size_t len, const void *emulate)
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{
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struct insn insn;
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int ret, i;
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int ret, i = 0;
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memcpy((void *)tp->text, opcode, len);
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if (len == 6)
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i = 1;
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memcpy((void *)tp->text, opcode+i, len-i);
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if (!emulate)
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emulate = opcode;
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@ -2053,6 +2078,13 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
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tp->len = len;
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tp->opcode = insn.opcode.bytes[0];
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if (is_jcc32(&insn)) {
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/*
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* Map Jcc.d32 onto Jcc.d8 and use len to distinguish.
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*/
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tp->opcode = insn.opcode.bytes[1] - 0x10;
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}
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switch (tp->opcode) {
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case RET_INSN_OPCODE:
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case JMP32_INSN_OPCODE:
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@ -2069,7 +2101,6 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
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BUG_ON(len != insn.length);
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}
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switch (tp->opcode) {
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case INT3_INSN_OPCODE:
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case RET_INSN_OPCODE:
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@ -2078,6 +2109,7 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
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case CALL_INSN_OPCODE:
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case JMP32_INSN_OPCODE:
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case JMP8_INSN_OPCODE:
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case 0x70 ... 0x7f: /* Jcc */
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tp->disp = insn.immediate.value;
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break;
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