The following commit has been merged into the x86/core branch of tip:
Commit-ID: d60ad3d46f1d04a282c56159f1deb675c12733fd
Gitweb: https://git.kernel.org/tip/d60ad3d46f1d04a282c56159f1deb675c12733fd
Author: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
AuthorDate: Wed, 03 Mar 2021 00:25:24 +09:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 23 Mar 2021 16:07:55 +01:00
x86/kprobes: Retrieve correct opcode for group instruction
Since the opcodes start from 0xff are group5 instruction group which is
not 2 bytes opcode but the extended opcode determined by the MOD/RM byte.
The commit abd82e533d88 ("x86/kprobes: Do not decode opcode in resume_execution()")
used insn->opcode.bytes[1], but that is not correct. We have to refer
the insn->modrm.bytes[1] instead.
Fixes: abd82e533d88 ("x86/kprobes: Do not decode opcode in resume_execution()")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/161469872400.49483.18214724458034233166.stgit@devnote2
---
arch/x86/kernel/kprobes/core.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 60a540f..9b31790 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -453,7 +453,11 @@ static void set_resume_flags(struct kprobe *p, struct insn *insn)
break;
#endif
case 0xff:
- opcode = insn->opcode.bytes[1];
+ /*
+ * Since the 0xff is an extended group opcode, the instruction
+ * is determined by the MOD/RM byte.
+ */
+ opcode = insn->modrm.bytes[0];
if ((opcode & 0x30) == 0x10) {
/*
* call absolute, indirect
|