[PATCH -tip v3 2/2] x86: kprobes: Prohibit probing on instruction which has emulate prefix

Masami Hiramatsu
2019-09-06T01:46:06Z

Prohibit probing on instruction which has XEN_EMULATE_PREFIX
or KVM's emulate prefix. Since that prefix is a marker for Xen
and KVM, if we modify the marker by kprobe's int3, that doesn't
work as expected.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
arch/x86/kernel/kprobes/core.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 43fc13c831af..4f13af7cbcdb 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -351,6 +351,10 @@ int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
kernel_insn_init(insn, dest, MAX_INSN_SIZE);
insn_get_length(insn);

+ /* We can not probe force emulate prefixed instruction */
+ if (insn_has_emulate_prefix(insn))
+ return 0;
+
/* Another subsystem puts a breakpoint, failed to recover */
if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
return 0;