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 v7 3/6] kprobes: checks probe address is instruction boudary on x86
Date: Sat, 23 May 2009 00:25:00 -0000 [thread overview]
Message-ID: <20090523002843.8948.65647.stgit@localhost.localdomain> (raw)
In-Reply-To: <20090523002830.8948.51194.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.
Changes from v5:
- Add comments to explain recover_probed_function() and decoding logic.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: 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 7b5169d..41d524f 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -48,12 +48,14 @@
#include <linux/preempt.h>
#include <linux/module.h>
#include <linux/kdebug.h>
+#include <linux/kallsyms.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
+#include <asm/insn.h>
void jprobe_return_end(void);
@@ -244,6 +246,71 @@ 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.
*/
@@ -359,6 +426,8 @@ 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
next prev parent reply other threads:[~2009-05-23 0:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-23 0:25 [PATCH -tip v7 0/6] tracing: kprobe-based event tracer and x86 instruction decoder Masami Hiramatsu
2009-05-23 0:25 ` [PATCH -tip v7 2/6] x86: x86 instruction decoder build-time selftest Masami Hiramatsu
2009-05-23 0:25 ` Masami Hiramatsu [this message]
2009-05-23 0:25 ` [PATCH -tip v7 1/6] x86: instruction decoder API Masami Hiramatsu
2009-05-23 0:52 ` [PATCH -tip v7 5/6] x86: add pt_regs register and stack access APIs Masami Hiramatsu
2009-05-23 0:52 ` [PATCH -tip v7 6/6] tracing: add kprobe-based event tracer Masami Hiramatsu
2009-05-23 0:52 ` [PATCH -tip v7 4/6] kprobes: cleanup fix_riprel() using insn decoder on x86 Masami Hiramatsu
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