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

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Message-Id: <156759756944.24473.4664241966878257420.stgit@devnote2>
Date:   Wed,  4 Sep 2019 20:46:09 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: [PATCH -tip 2/2] x86: kprobes: Prohibit probing on instruction which has Xen prefix

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@...nel.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;