From: Peter Zijlstra peterz@infradead.org
commit 26c44b776dba4ac692a0bf5a3836feb8a63fea6b upstream.
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@infradead.org Signed-off-by: Borislav Petkov bp@suse.de Link: https://lore.kernel.org/r/20211204134908.082342723@infradead.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/alternative.c | 49 +++++++++++++++++++++++++++++------------- 1 file changed, 34 insertions(+), 15 deletions(-)
--- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1243,10 +1243,13 @@ 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; };
@@ -1261,7 +1264,8 @@ 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; @@ -1295,7 +1299,7 @@ noinstr int poke_int3_handler(struct pt_ { struct bp_patching_desc *desc; struct text_poke_loc *tp; - int len, ret = 0; + int ret = 0; void *ip;
if (user_mode(regs)) @@ -1335,8 +1339,7 @@ noinstr int poke_int3_handler(struct pt_ goto out_put; }
- len = text_opcode_size(tp->opcode); - ip += len; + ip += tp->len;
switch (tp->opcode) { case INT3_INSN_OPCODE: @@ -1351,12 +1354,12 @@ noinstr int poke_int3_handler(struct pt_ 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: @@ -1431,7 +1434,7 @@ static void text_poke_bp_batch(struct te */ 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, @@ -1508,21 +1511,37 @@ static void text_poke_loc_init(struct te 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; @@ -1530,7 +1549,7 @@ static void text_poke_loc_init(struct te 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 */ @@ -1538,13 +1557,13 @@ static void text_poke_loc_init(struct te case 2: /* NOP2 -- emulate as JMP8+0 */ BUG_ON(memcmp(emulate, ideal_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, ideal_nops[NOP_ATOMIC5], len)); tp->opcode = JMP32_INSN_OPCODE; - tp->rel32 = 0; + tp->disp = 0; break;
default: /* unknown instruction */