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

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Message-ID: <20220510133036.46767-5-mheyne@amazon.de>
Date:   Tue, 10 May 2022 13:30:33 +0000
From:   Maximilian Heyne <mheyne@...zon.de>
To:     unlisted-recipients:; (no To-header on input)
CC:     Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>, <x86@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Borislav Petkov <bp@...en8.de>,
        <xen-devel@...ts.xenproject.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Maximilian Heyne <mheyne@...zon.de>, <stable@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
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        Namhyung Kim <namhyung@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: [PATCH 4/4] x86: kprobes: Prohibit probing on instruction which has emulate prefix

From: Masami Hiramatsu <mhiramat@...nel.org>

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@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Juergen Gross <jgross@...e.com>
Cc: x86@...nel.org
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Stefano Stabellini <sstabellini@...nel.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: xen-devel@...ts.xenproject.org
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/156777566048.25081.6296162369492175325.stgit@devnote2
Signed-off-by: Maximilian Heyne <mheyne@...zon.de>
Cc: stable@...r.kernel.org # 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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