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

Masami Hiramatsu
2019-09-04T11:46:16Z

Prohibit probing on instruction which has XEN_EMULATE_PREFIX
(it must be cpuid.) Since that prefix is a marker for Xen,
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..b1e86af4a985 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 XEN_EMULATE_PREFIX instruction */
+ if (insn_has_xen_prefix(insn))
+ return 0;
+
/* Another subsystem puts a breakpoint, failed to recover */
if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
return 0;