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x86: kprobes checks safeness of insertion address.

PATCH In review Masami Hiramatsu 3 participants 6 messages Apr 2, 2009 – Apr 3, 2009

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Masami Hiramatsu

author
#0 lore raw

PATCH v4 4/6 x86: kprobes checks safeness of insertion address.

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 <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Jim Keniston <[email protected]>
Cc Ingo Molnar <[email protected]>

---

 arch/x86/kernel/kprobes.c |   51 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)
arch/x86/kernel/kprobes.c +51 -0
index 7b5169d..39c79cc 100644
@@ -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)
Signature · 7 lines
Masami Hiramatsu

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

e-mail: [email protected]
#1 lore raw
Quoted 9 lines · Masami Hiramatsu
arch/x86/kernel/kprobes.c +9 -0
+/* 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 */

arch/x86/kernel/kprobes.c retry: · line 267

Quoted 10 lines
arch/x86/kernel/kprobes.c +10 -0
+	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

author
#2 lore raw

PATCH 4/6 x86: kprobes checks safeness of insertion address.

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.

changes from v4:
- change a comment according to Ananth's suggestion.

Signed-off-by Masami Hiramatsu <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Jim Keniston <[email protected]>
Cc Ingo Molnar <[email protected]>

---

 arch/x86/kernel/kprobes.c |   51 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)
arch/x86/kernel/kprobes.c +51 -0
index 7b5169d..e4f36e7 100644
@@ -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 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];
+
+	/* 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)
Signature · 7 lines
Masami Hiramatsu

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

e-mail: [email protected]
#3 lore raw
Quoted 18 lines · Masami Hiramatsu

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.

changes from v4:
- change a comment according to Ananth's suggestion.

Signed-off-by Masami Hiramatsu <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Jim Keniston <[email protected]>
Cc Ingo Molnar <[email protected]>

---

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

...

Quoted 2 lines

+/* Recover original instruction */

/* Recover the probed instruction at addr for further analysis. */ See below.

arch/x86/kernel/kprobes.c retry: · line 257

Quoted 8 lines
arch/x86/kernel/kprobes.c +8 -0
+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 */

fix_riprel doesn't affect the instruction's length, which is what concerns this patch. But we want this function to be useful for unforeseen uses as well, so I like the code you have. Just consider the suggested comment changes.

	/*
	 * Don't use p->ainsn.insn, which could be modified -- e.g.,
	 * by fix_riprel().
	 */

arch/x86/kernel/kprobes.c retry: · line 261

Quoted 4 lines
arch/x86/kernel/kprobes.c +4 -0
+	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	buf[0] = kp->opcode;
+	return 0;
+}

Jim Keniston

author
#4 lore raw
Quoted 18 lines · Jim Keniston
Quoted 17 lines · Masami Hiramatsu

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.

changes from v4:
- change a comment according to Ananth's suggestion.

Signed-off-by Masami Hiramatsu <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Jim Keniston <[email protected]>
Cc Ingo Molnar <[email protected]>

---

 arch/x86/kernel/kprobes.c |   51 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)
Quoted 6 lines
Quoted 1 line
arch/x86/kernel/kprobes.c +0 -0

...

Quoted 1 line

+/* Recover original instruction */

/* Recover the probed instruction at addr for further analysis. */ See below.

Sure.

Quoted 15 lines

arch/x86/kernel/kprobes.c retry: · line 257

Quoted 9 lines
arch/x86/kernel/kprobes.c +8 -0
+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 */

fix_riprel doesn't affect the instruction's length, which is what concerns this patch. But we want this function to be useful for unforeseen uses as well, so I like the code you have. Just consider the suggested comment changes.

Quoted 4 lines
	/*
	 * Don't use p->ainsn.insn, which could be modified -- e.g.,
	 * by fix_riprel().
	 */

Thanks, I'll update comments then!

Quoted 13 lines

arch/x86/kernel/kprobes.c retry: · line 261

Quoted 5 lines
arch/x86/kernel/kprobes.c +4 -0
+	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	buf[0] = kp->opcode;
+	return 0;
+}

Jim Keniston

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Signature · 7 lines
Masami Hiramatsu

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

e-mail: [email protected]
author
#5 lore raw

PATCH 4/6 x86: kprobes checks safeness of insertion address.

x86: kprobes checks safeness of insertion address.

From: Masami Hiramatsu <[email protected]>

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.

changes from v4.1:
- update comments according to Jim's suggestion.
- s/lookup_symbol_attrs/kallsyms_lookup/ in a comment.

Signed-off-by Masami Hiramatsu <[email protected]>
Cc Ananth N Mavinakayanahalli <[email protected]>
Cc Jim Keniston <[email protected]>
Cc Ingo Molnar <[email protected]>

---

 arch/x86/kernel/kprobes.c |   54 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 54 insertions(+), 0 deletions(-)
arch/x86/kernel/kprobes.c +54 -0
index 7b5169d..3d5e85f 100644
@@ -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 +246,56 @@ 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;
+
+	/*
+	 * Don't use p->ainsn.insn, which could be modified -- e.g.,
+	 * by fix_riprel().
+	 */
+	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];
+
+	/* 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 +411,8 @@ 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)
Signature · 7 lines
Masami Hiramatsu

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

e-mail: [email protected]