linux-kernel - [RFC PATCH 1/2] kprobes/x86: Use probe_kernel

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Date:   Tue, 28 Feb 2017 01:13:28 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC PATCH 1/2] kprobes/x86: Use probe_kernel_read instead of memcpy

Use probe_kernel_read() for avoiding unexpected faults while
copying kernel text in both of __recover_probed_insn() and
__recover_optprobed_insn().

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/x86/kernel/kprobes/core.c |    7 +++++--
 arch/x86/kernel/kprobes/opt.c  |    5 ++++-
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6384eb7..34d3a52 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -264,7 +264,10 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
 	 * Fortunately, we know that the original code is the ideal 5-byte
 	 * long NOP.
 	 */
-	memcpy(buf, (void *)addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	if (probe_kernel_read(buf, (void *)addr,
+		MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
+		return 0UL;
+
 	if (faddr)
 		memcpy(buf, ideal_nops[NOP_ATOMIC5], 5);
 	else
@@ -276,7 +279,7 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
  * Recover the probed instruction at addr for further analysis.
  * Caller must lock kprobes by kprobe_mutex, or disable preemption
  * for preventing to release referencing kprobes.
- * Returns zero if the instruction can not get recovered.
+ * Returns zero if the instruction can not get recovered (or access failed).
  */
 unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
 {
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 3d1bee9..06ddd0b 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -65,7 +65,10 @@ unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
 	 * overwritten by jump destination address. In this case, original
 	 * bytes must be recovered from op->optinsn.copied_insn buffer.
 	 */
-	memcpy(buf, (void *)addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+	if (probe_kernel_read(buf, (void *)addr,
+		MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
+		return 0UL;
+
 	if (addr == (unsigned long)kp->addr) {
 		buf[0] = kp->opcode;
 		memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);