linux-kernel - [PATCH -tip v6 2/2] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

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Message-Id: <150124474863.6501.3639381952373012501.stgit@devbox>
Date:   Fri, 28 Jul 2017 21:25:58 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Francis Deslauriers <francis.deslauriers@...icios.com>,
        mathieu.desnoyers@...icios.com, Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ananth N Mavinakayanahalli <ananth@...ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: [PATCH -tip v6 2/2] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

Since the kernel segment registers are not prepared at the
entry of irq-entry code, if a kprobe on such code is
jump-optimized, accessing per-cpu variables may cause
kernel panic.
However, if the kprobe is not optimized, it kicks int3
exception and set segment registers correctly.

This checks probe-address and if it is in irq-entry code,
it prohibits optimizing such kprobes. This means we can
continuously probing such interrupt handlers by kprobes
but it is not optimized anymore.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Reported-by: Francis Deslauriers <francis.deslauriers@...icios.com>
Tested-by: Francis Deslauriers <francis.deslauriers@...icios.com>
---
 Changes in v6:
  - Update for unconditional irqentry.
---
 arch/x86/kernel/kprobes/opt.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 69ea0bc1cfa3..4f98aad38237 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -39,6 +39,7 @@
 #include <asm/insn.h>
 #include <asm/debugreg.h>
 #include <asm/set_memory.h>
+#include <asm/sections.h>
 
 #include "common.h"
 
@@ -251,10 +252,12 @@ static int can_optimize(unsigned long paddr)
 
 	/*
 	 * Do not optimize in the entry code due to the unstable
-	 * stack handling.
+	 * stack handling and registers setup.
 	 */
-	if ((paddr >= (unsigned long)__entry_text_start) &&
-	    (paddr <  (unsigned long)__entry_text_end))
+	if (((paddr >= (unsigned long)__entry_text_start) &&
+	     (paddr <  (unsigned long)__entry_text_end)) ||
+	    ((paddr >= (unsigned long)__irqentry_text_start) &&
+	     (paddr <  (unsigned long)__irqentry_text_end)))
 		return 0;
 
 	/* Check there is enough space for a relative jump. */