[PATCH -tip v4 4/4] x86: kprobes: Prohibit probing on instruction which has emulate prefix

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Andrew Cooper <andrew.cooper3@citrix.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 v4 4/4] x86: kprobes: Prohibit probing on instruction which has emulate prefix
Date: Fri,  6 Sep 2019 22:14:20 +0900	[thread overview]
Message-ID: <156777566048.25081.6296162369492175325.stgit@devnote2> (raw)
In-Reply-To: <156777561745.25081.1205321122446165328.stgit@devnote2>

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;

