The following commit has been merged into the x86/core branch of tip: Commit-ID: 26c44b776dba4ac692a0bf5a3836feb8a63fea6b Gitweb: https://git.kernel.org/tip/26c44b776dba4ac692a0bf5a3836feb8a63fea6b Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Sat, 04 Dec 2021 14:43:43 +01:00 Committer: Borislav Petkov <bp@xxxxxxx> CommitterDate: Thu, 09 Dec 2021 11:04:50 +01:00 x86/alternative: Relax text_poke_bp() constraint Currently, text_poke_bp() is very strict to only allow patching a single instruction; however with straight-line-speculation it will be required to patch: ret; int3, which is two instructions. As such, relax the constraints a little to allow int3 padding for all instructions that do not imply the execution of the next instruction, ie: RET, JMP.d8 and JMP.d32. While there, rename the text_poke_loc::rel32 field to ::disp. Note: this fills up the text_poke_loc structure which is now a round 16 bytes big. [ bp: Put comments ontop instead of on the side. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Link: https://lore.kernel.org/r/20211204134908.082342723@xxxxxxxxxxxxx --- arch/x86/kernel/alternative.c | 49 +++++++++++++++++++++++----------- 1 file changed, 34 insertions(+), 15 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 175cde6..5007c3f 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1113,10 +1113,13 @@ void text_poke_sync(void) } struct text_poke_loc { - s32 rel_addr; /* addr := _stext + rel_addr */ - s32 rel32; + /* addr := _stext + rel_addr */ + s32 rel_addr; + s32 disp; + u8 len; u8 opcode; const u8 text[POKE_MAX_OPCODE_SIZE]; + /* see text_poke_bp_batch() */ u8 old; }; @@ -1131,7 +1134,8 @@ static struct bp_patching_desc *bp_desc; static __always_inline struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp) { - struct bp_patching_desc *desc = __READ_ONCE(*descp); /* rcu_dereference */ + /* rcu_dereference */ + struct bp_patching_desc *desc = __READ_ONCE(*descp); if (!desc || !arch_atomic_inc_not_zero(&desc->refs)) return NULL; @@ -1165,7 +1169,7 @@ noinstr int poke_int3_handler(struct pt_regs *regs) { struct bp_patching_desc *desc; struct text_poke_loc *tp; - int len, ret = 0; + int ret = 0; void *ip; if (user_mode(regs)) @@ -1205,8 +1209,7 @@ noinstr int poke_int3_handler(struct pt_regs *regs) goto out_put; } - len = text_opcode_size(tp->opcode); - ip += len; + ip += tp->len; switch (tp->opcode) { case INT3_INSN_OPCODE: @@ -1221,12 +1224,12 @@ noinstr int poke_int3_handler(struct pt_regs *regs) break; case CALL_INSN_OPCODE: - int3_emulate_call(regs, (long)ip + tp->rel32); + int3_emulate_call(regs, (long)ip + tp->disp); break; case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: - int3_emulate_jmp(regs, (long)ip + tp->rel32); + int3_emulate_jmp(regs, (long)ip + tp->disp); break; default: @@ -1301,7 +1304,7 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries */ for (do_sync = 0, i = 0; i < nr_entries; i++) { u8 old[POKE_MAX_OPCODE_SIZE] = { tp[i].old, }; - int len = text_opcode_size(tp[i].opcode); + int len = tp[i].len; if (len - INT3_INSN_SIZE > 0) { memcpy(old + INT3_INSN_SIZE, @@ -1378,21 +1381,37 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr, const void *opcode, size_t len, const void *emulate) { struct insn insn; - int ret; + int ret, i; memcpy((void *)tp->text, opcode, len); if (!emulate) emulate = opcode; ret = insn_decode_kernel(&insn, emulate); - BUG_ON(ret < 0); - BUG_ON(len != insn.length); tp->rel_addr = addr - (void *)_stext; + tp->len = len; tp->opcode = insn.opcode.bytes[0]; switch (tp->opcode) { + case RET_INSN_OPCODE: + case JMP32_INSN_OPCODE: + case JMP8_INSN_OPCODE: + /* + * Control flow instructions without implied execution of the + * next instruction can be padded with INT3. + */ + for (i = insn.length; i < len; i++) + BUG_ON(tp->text[i] != INT3_INSN_OPCODE); + break; + + default: + BUG_ON(len != insn.length); + }; + + + switch (tp->opcode) { case INT3_INSN_OPCODE: case RET_INSN_OPCODE: break; @@ -1400,7 +1419,7 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr, case CALL_INSN_OPCODE: case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: - tp->rel32 = insn.immediate.value; + tp->disp = insn.immediate.value; break; default: /* assume NOP */ @@ -1408,13 +1427,13 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr, case 2: /* NOP2 -- emulate as JMP8+0 */ BUG_ON(memcmp(emulate, x86_nops[len], len)); tp->opcode = JMP8_INSN_OPCODE; - tp->rel32 = 0; + tp->disp = 0; break; case 5: /* NOP5 -- emulate as JMP32+0 */ BUG_ON(memcmp(emulate, x86_nops[len], len)); tp->opcode = JMP32_INSN_OPCODE; - tp->rel32 = 0; + tp->disp = 0; break; default: /* unknown instruction */
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