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From: Masami Hiramatsu <mhiramat@redhat.com>
To: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
	lkml <linux-kernel@vger.kernel.org>
Cc: systemtap <systemtap@sources.redhat.com>,
	kvm <kvm@vger.kernel.org>,
	DLE <dle-develop@lists.sourceforge.net>,
	Masami Hiramatsu <mhiramat@redhat.com>,
	Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
	Jim Keniston <jkenisto@us.ibm.com>, Ingo Molnar <mingo@elte.hu>
Subject: [PATCH -tip -v11 03/11] kprobes: checks probe address is instruction boudary on x86
Date: Thu, 09 Jul 2009 16:22:41 -0400	[thread overview]
Message-ID: <20090709202241.13223.11317.stgit@localhost.localdomain> (raw)
In-Reply-To: <20090709202220.13223.97114.stgit@localhost.localdomain>

Ensure safeness of inserting kprobes by checking whether the specified
address is at the first byte of a instruction on x86.
This is done by decoding probed function from its head to the probe point.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
---

 arch/x86/kernel/kprobes.c |   69 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 69 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index b5b1848..5341842 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -48,6 +48,7 @@
 #include <linux/preempt.h>
 #include <linux/module.h>
 #include <linux/kdebug.h>
+#include <linux/kallsyms.h>
 
 #include <asm/cacheflush.h>
 #include <asm/desc.h>
@@ -55,6 +56,7 @@
 #include <asm/uaccess.h>
 #include <asm/alternative.h>
 #include <asm/debugreg.h>
+#include <asm/insn.h>
 
 void jprobe_return_end(void);
 
@@ -245,6 +247,71 @@ retry:
 	}
 }
 
+/* Recover the probed instruction at addr for further analysis. */
+static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
+{
+	struct kprobe *kp;
+	kp = get_kprobe((void *)addr);
+	if (!kp)
+		return -EINVAL;
+
+	/*
+	 *  Basically, kp->ainsn.insn has an original instruction.
+	 *  However, RIP-relative instruction can not do single-stepping
+	 *  at different place, fix_riprel() tweaks the displacement of
+	 *  that instruction. In that case, we can't recover the instruction
+	 *  from the kp->ainsn.insn.
+	 *
+	 *  On the other hand, kp->opcode has a copy of the first byte of
+	 *  the probed instruction, which is overwritten by int3. And
+	 *  the instruction at kp->addr is not modified by kprobes except
+	 *  for the first byte, we can recover the original instruction
+	 *  from it and kp->opcode.
+	 */
+	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	buf[0] = kp->opcode;
+	return 0;
+}
+
+/* Dummy buffers for kallsyms_lookup */
+static char __dummy_buf[KSYM_NAME_LEN];
+
+/* Check if paddr is at an instruction boundary */
+static int __kprobes can_probe(unsigned long paddr)
+{
+	int ret;
+	unsigned long addr, offset = 0;
+	struct insn insn;
+	kprobe_opcode_t buf[MAX_INSN_SIZE];
+
+	if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf))
+		return 0;
+
+	/* Decode instructions */
+	addr = paddr - offset;
+	while (addr < paddr) {
+		kernel_insn_init(&insn, (void *)addr);
+		insn_get_opcode(&insn);
+
+		/* Check if the instruction has been modified. */
+		if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) {
+			ret = recover_probed_instruction(buf, addr);
+			if (ret)
+				/*
+				 * Another debugging subsystem might insert
+				 * this breakpoint. In that case, we can't
+				 * recover it.
+				 */
+				return 0;
+			kernel_insn_init(&insn, buf);
+		}
+		insn_get_length(&insn);
+		addr += insn.length;
+	}
+
+	return (addr == paddr);
+}
+
 /*
  * Returns non-zero if opcode modifies the interrupt flag.
  */
@@ -360,6 +427,8 @@ static void __kprobes arch_copy_kprobe(struct kprobe *p)
 
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
+	if (!can_probe((unsigned long)p->addr))
+		return -EILSEQ;
 	/* insn: must be on special executable page on x86. */
 	p->ainsn.insn = get_insn_slot();
 	if (!p->ainsn.insn)


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com

  parent reply	other threads:[~2009-07-09 20:20 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-07-09 20:22 [PATCH -tip -v11 00/11] tracing: kprobe-based event tracer and x86 instruction decoder Masami Hiramatsu
2009-07-09 20:22 ` Masami Hiramatsu
2009-07-09 20:22 ` [PATCH -tip -v11 01/11] x86: instruction decoder API Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22 ` [PATCH -tip -v11 02/11] x86: x86 instruction decoder build-time selftest Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22 ` Masami Hiramatsu [this message]
2009-07-09 20:22 ` [PATCH -tip -v11 04/11] kprobes: cleanup fix_riprel() using insn decoder on x86 Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22 ` [PATCH -tip -v11 05/11] x86: add pt_regs register and stack access APIs Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22   ` Masami Hiramatsu
2009-07-09 20:22 ` [PATCH -tip -v11 06/11] tracing: ftrace dynamic ftrace_event_call support Masami Hiramatsu
2009-07-09 20:23 ` [PATCH -tip -v11 07/11] tracing: Introduce TRACE_FIELD_ZERO() macro Masami Hiramatsu
2009-07-09 20:23 ` [PATCH -tip -v11 08/11] tracing: add kprobe-based event tracer Masami Hiramatsu
2009-07-09 20:23   ` Masami Hiramatsu
2009-07-10  7:13   ` Li Zefan
2009-07-10 20:33     ` Masami Hiramatsu
2009-07-10 20:33       ` Masami Hiramatsu
2009-07-09 20:23 ` [PATCH -tip -v11 09/11] tracing: Kprobe-tracer supports more than 6 arguments Masami Hiramatsu
2009-07-09 20:23   ` Masami Hiramatsu
2009-07-09 20:23 ` [PATCH -tip -v11 10/11] tracing: Generate names for each kprobe event automatically Masami Hiramatsu
2009-07-09 20:23   ` Masami Hiramatsu
2009-07-09 20:23 ` [PATCH -tip -v11 11/11] tracing: Add kprobes event profiling interface Masami Hiramatsu
2009-07-09 20:23   ` Masami Hiramatsu
2009-07-10  5:17   ` Ananth N Mavinakayanahalli
2009-07-10  6:46   ` Li Zefan
2009-07-10  6:46     ` Li Zefan
2009-07-10 19:59     ` Masami Hiramatsu
2009-07-10 19:59       ` Masami Hiramatsu

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