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

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Borislav Petkov <bp@alien8.de>, Juergen Gross <jgross@suse.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	xen-devel@lists.xenproject.org
Subject: [PATCH -tip 2/2] x86: kprobes: Prohibit probing on instruction which has Xen prefix
Date: Wed,  4 Sep 2019 20:46:09 +0900	[thread overview]
Message-ID: <156759756944.24473.4664241966878257420.stgit@devnote2> (raw)
In-Reply-To: <156759754770.24473.11832897710080799131.stgit@devnote2>

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;

