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[RFC PATCH 1/2] kprobes/x86: Use probe_kernel_read instead of memcpy

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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@kernel.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);

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Thread

kprobes vs __ex_table[] Peter Zijlstra <peterz@infradead.org> - 2017-02-23 19:40 +0100
  Re: kprobes vs __ex_table[] Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-24 02:10 +0100
    Re: kprobes vs __ex_table[] Peter Zijlstra <peterz@infradead.org> - 2017-02-24 10:30 +0100
      Re: kprobes vs __ex_table[] Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-24 17:40 +0100
        Re: kprobes vs __ex_table[] Peter Zijlstra <peterz@infradead.org> - 2017-02-24 18:50 +0100
          [RFC PATCH 1/2] kprobes/x86: Use probe_kernel_read instead of memcpy Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-27 17:20 +0100
          [RFC PATCH 2/2] kprobes/x86: Exit single-stepping before trying fixup_exception Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-27 17:20 +0100
          [RFC PATCH 0/2] kprobes/x86: Handle probing on ex_table cases Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-27 17:20 +0100
      Re: kprobes vs __ex_table[] Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-28 17:30 +0100
        [PATCH] [BUGFIX] kprobes/x86: Fix to check __ex_table entry by probed address Masami Hiramatsu <mhiramat@kernel.org> - 2017-02-28 18:50 +0100

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