linux-kernel - [PATCH 4.4 106/159] uprobes/x86: Prohibit probing on MOV SS instruction

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Message-Id: <20191122100824.676608025@linuxfoundation.org>
Date:   Fri, 22 Nov 2019 11:28:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Francis Deslauriers <francis.deslauriers@...icios.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, Yonghong Song <yhs@...com>,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 106/159] uprobes/x86: Prohibit probing on MOV SS instruction

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

commit 13ebe18c94f5b0665c01ae7fad2717ae959f4212 upstream.

Since MOV SS and POP SS instructions will delay the exceptions until the
next instruction is executed, single-stepping on it by uprobes must be
prohibited.

uprobe already rejects probing on POP SS (0x1f), but allows probing on MOV
SS (0x8e and reg == 2).  This checks the target instruction and if it is
MOV SS or POP SS, returns -ENOTSUPP to reject probing.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: Francis Deslauriers <francis.deslauriers@...icios.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Yonghong Song <yhs@...com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "David S . Miller" <davem@...emloft.net>
Link: https://lkml.kernel.org/r/152587072544.17316.5950935243917346341.stgit@devbox
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/uprobes.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -296,6 +296,10 @@ static int uprobe_init_insn(struct arch_
 	if (is_prefix_bad(insn))
 		return -ENOTSUPP;

+	/* We should not singlestep on the exception masking instructions */
+	if (insn_masking_exception(insn))
+		return -ENOTSUPP;
+
 	if (x86_64)
 		good_insns = good_insns_64;
 	else