2022-11-29 08:51:23

by Chuang Wang

Subject: [PATCH] x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

For the `FF /digit` opcodes in prepare_emulation, use switch-case
instead of hand-written code to make the logic easier to understand.

Signed-off-by: Chuang Wang <[email protected]>
---
arch/x86/kernel/kprobes/core.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 66299682b6b7..66ec32b6cd0e 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -655,17 +655,19 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn)
* is determined by the MOD/RM byte.
*/
opcode = insn->modrm.bytes[0];
- if ((opcode & 0x30) == 0x10) {
- if ((opcode & 0x8) == 0x8)
- return -EOPNOTSUPP; /* far call */
- /* call absolute, indirect */
+ switch (X86_MODRM_REG(opcode)) {
+ case 0b010: /* FF /2, call near, absolute indirect */
p->ainsn.emulate_op = kprobe_emulate_call_indirect;
- } else if ((opcode & 0x30) == 0x20) {
- if ((opcode & 0x8) == 0x8)
- return -EOPNOTSUPP; /* far jmp */
- /* jmp near absolute indirect */
+ break;
+ case 0b100: /* FF /4, jmp near, absolute indirect */
p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
- } else
+ break;
+ case 0b011: /* FF /3, call far, absolute indirect */
+ case 0b101: /* FF /5, jmp far, absolute indirect */
+ return -EOPNOTSUPP;
+ }
+
+ if (!p->ainsn.emulate_op)
break;

if (insn->addr_bytes != sizeof(unsigned long))
--
2.37.2

2022-11-30 14:06:16

by Masami Hiramatsu

Subject: Re: [PATCH] x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

On Tue, 29 Nov 2022 16:39:51 +0800
Chuang Wang <[email protected]> wrote:

> For the `FF /digit` opcodes in prepare_emulation, use switch-case
> instead of hand-written code to make the logic easier to understand.
>
> Signed-off-by: Chuang Wang <[email protected]>

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <[email protected]>

Thank you!

> ---
> arch/x86/kernel/kprobes/core.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 66299682b6b7..66ec32b6cd0e 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -655,17 +655,19 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn)
> * is determined by the MOD/RM byte.
> */
> opcode = insn->modrm.bytes[0];
> - if ((opcode & 0x30) == 0x10) {
> - if ((opcode & 0x8) == 0x8)
> - return -EOPNOTSUPP; /* far call */
> - /* call absolute, indirect */
> + switch (X86_MODRM_REG(opcode)) {
> + case 0b010: /* FF /2, call near, absolute indirect */
> p->ainsn.emulate_op = kprobe_emulate_call_indirect;
> - } else if ((opcode & 0x30) == 0x20) {
> - if ((opcode & 0x8) == 0x8)
> - return -EOPNOTSUPP; /* far jmp */
> - /* jmp near absolute indirect */
> + break;
> + case 0b100: /* FF /4, jmp near, absolute indirect */
> p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
> - } else
> + break;
> + case 0b011: /* FF /3, call far, absolute indirect */
> + case 0b101: /* FF /5, jmp far, absolute indirect */
> + return -EOPNOTSUPP;
> + }
> +
> + if (!p->ainsn.emulate_op)
> break;
>
> if (insn->addr_bytes != sizeof(unsigned long))
> --
> 2.37.2
>


--
Masami Hiramatsu (Google) <[email protected]>

2023-01-10 12:09:54

by tip-bot2 for Jacob Pan

Subject: [tip: perf/core] x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

The following commit has been merged into the perf/core branch of tip:

Commit-ID: 9fcad995c6c52cc9791f7ee9f1386a5684055f9c
Gitweb: https://git.kernel.org/tip/9fcad995c6c52cc9791f7ee9f1386a5684055f9c
Author: Chuang Wang <[email protected]>
AuthorDate: Tue, 29 Nov 2022 16:39:51 +08:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Tue, 10 Jan 2023 12:37:14 +01:00

x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

For the `FF /digit` opcodes in prepare_emulation, use switch-case
instead of hand-written code to make the logic easier to understand.

Signed-off-by: Chuang Wang <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/kernel/kprobes/core.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 33390ed..fd0420a 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -655,17 +655,19 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn)
* is determined by the MOD/RM byte.
*/
opcode = insn->modrm.bytes[0];
- if ((opcode & 0x30) == 0x10) {
- if ((opcode & 0x8) == 0x8)
- return -EOPNOTSUPP; /* far call */
- /* call absolute, indirect */
+ switch (X86_MODRM_REG(opcode)) {
+ case 0b010: /* FF /2, call near, absolute indirect */
p->ainsn.emulate_op = kprobe_emulate_call_indirect;
- } else if ((opcode & 0x30) == 0x20) {
- if ((opcode & 0x8) == 0x8)
- return -EOPNOTSUPP; /* far jmp */
- /* jmp near absolute indirect */
+ break;
+ case 0b100: /* FF /4, jmp near, absolute indirect */
p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
- } else
+ break;
+ case 0b011: /* FF /3, call far, absolute indirect */
+ case 0b101: /* FF /5, jmp far, absolute indirect */
+ return -EOPNOTSUPP;
+ }
+
+ if (!p->ainsn.emulate_op)
break;

if (insn->addr_bytes != sizeof(unsigned long))