[-tip,4/6,V4] x86: kprobes checks safeness of insertion address.

Commit Message

Masami Hiramatsu April 2, 2009, 5:24 p.m. UTC

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

Signed-off-by: Masami Hiramatsu <[e-mail]>
Cc: Ananth N Mavinakayanahalli <[e-mail]>
Cc: Jim Keniston <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
---

 arch/x86/kernel/kprobes.c |   51 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)

Comments

Ananth N Mavinakayanahalli April 3, 2009, 5:18 a.m. UTC | #1

On Thu, Apr 02, 2009 at 01:24:57PM -0400, Masami Hiramatsu wrote:
 
> +/* Recover original instruction */
> +static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
> +{
> +	struct kprobe *kp;
> +	kp = get_kprobe((void *)addr);
> +	if (!kp)
> +		return -EINVAL;
> +
> +	/* Don't use p->ainsn.insn; which will be modified by fix_riprel */
> +	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
> +	buf[0] = kp->opcode;
> +	return 0;
> +}
> +
> +/* Dummy buffers for lookup_symbol_attrs */
> +static char __dummy_buf[KSYM_NAME_LEN];
> +
> +/* Check whether the address can be probed */
> +static int __kprobes can_probe(unsigned long paddr)

A better description would've been "Check if paddr is at an instruction
boundary". Otherwise looks good.

Ananth
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Patch

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d..39c79cc 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 +246,53 @@  retry:
 	}
 }

+/* Recover original instruction */
+static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
+{
+	struct kprobe *kp;
+	kp = get_kprobe((void *)addr);
+	if (!kp)
+		return -EINVAL;
+
+	/* Don't use p->ainsn.insn; which will be modified by fix_riprel */
+	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	buf[0] = kp->opcode;
+	return 0;
+}
+
+/* Dummy buffers for lookup_symbol_attrs */
+static char __dummy_buf[KSYM_NAME_LEN];
+
+/* Check whether the address can be probed */
+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];
+
+	/* Lookup symbol including addr */
+	if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf))
+		return 0;
+
+	/* Decode instructions */
+	addr = paddr - offset;
+	while (addr < paddr) {
+		insn_init_kernel(&insn, (void *)addr);
+		insn_get_opcode(&insn);
+		if (OPCODE1(&insn) == BREAKPOINT_INSTRUCTION) {
+			ret = recover_probed_instruction(buf, addr);
+			if (ret)
+				return 0;
+			insn_init_kernel(&insn, buf);
+		}
+		insn_get_length(&insn);
+		addr += insn.length;
+	}
+
+	return (addr == paddr);
+}
+
 /*
  * Returns non-zero if opcode modifies the interrupt flag.
  */
@@ -359,6 +408,8 @@  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)