[PATCH 4/4] x86: kprobes: Prohibit probing on instruction which has emulate prefix

[Maximilian Heyne <mheyne@xxxxxxxxx>]

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit 004e8dce9c5595697951f7cd0e9f66b35c92265e upstream

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: 
https://lkml.kernel.org/r/156777566048.25081.6296162369492175325.stgit@devnote2
Signed-off-by: Maximilian Heyne <mheyne@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.4.x
---
 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 c205d77d57da..3700dc94847c 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -358,6 +358,10 @@ 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;
-- 
2.32.0




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