[PATCH] kprobes: x86: cleanup __recover_probed_insn().

[Wang Nan]

Since kernel kconfig forbids turning off KPROBES_ON_FTRACE for x86, we
don't need to consider the situation that a kprobe probing on a ftrace
location. The only exception should be early kprobe with
KPROBES_ON_FTRACE enabled. However, it is still impossible for it to get
a tainted by ftrace if it is registered before ftrace is ready.

Thus this patch removes unneed logic to make code simpler.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
 arch/x86/kernel/kprobes/core.c | 62 ++++++++----------------------------------
 1 file changed, 12 insertions(+), 50 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 4e3d5a9..88a99c0 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -219,55 +219,6 @@ retry:
 	}
 }
 
-static unsigned long
-__recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
-{
-	struct kprobe *kp;
-	unsigned long faddr;
-
-	kp = get_kprobe((void *)addr);
-	faddr = ftrace_location(addr);
-	/*
-	 * Addresses inside the ftrace location are refused by
-	 * arch_check_ftrace_location(). Something went terribly wrong
-	 * if such an address is checked here.
-	 */
-	if (WARN_ON(faddr && faddr != addr))
-		return 0UL;
-	/*
-	 * Use the current code if it is not modified by Kprobe
-	 * and it cannot be modified by ftrace.
-	 */
-	if (!kp && !faddr)
-		return addr;
-
-	/*
-	 * Basically, kp->ainsn.insn has an original instruction.
-	 * However, RIP-relative instruction can not do single-stepping
-	 * at different place, __copy_instruction() tweaks the displacement of
-	 * that instruction. In that case, we can't recover the instruction
-	 * from the kp->ainsn.insn.
-	 *
-	 * On the other hand, in case on normal Kprobe, 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.
-	 *
-	 * In case of Kprobes using ftrace, we do not have a copy of
-	 * the original instruction. In fact, the ftrace location might
-	 * be modified at anytime and even could be in an inconsistent state.
-	 * 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 (faddr)
-		memcpy(buf, ideal_nops[NOP_ATOMIC5], 5);
-	else
-		buf[0] = kp->opcode;
-	return (unsigned long)buf;
-}
-
 /*
  * Recover the probed instruction at addr for further analysis.
  * Caller must lock kprobes by kprobe_mutex, or disable preemption
@@ -282,7 +233,18 @@ unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long add
 	if (__addr != addr)
 		return __addr;
 
-	return __recover_probed_insn(buf, addr);
+	/*
+	 * If KPROBES_ON_FTRACE is off, we are not allowed probing at
+	 * ftrace location. If it is on, we should use
+	 * arm_kprobe_ftrace() and never get here.  As a result, there
+	 * is no need to care about confliction between kprobe and
+	 * ftrace. The only exception should be early kprobes. However,
+	 * for such kprobes registered before ftrace is ready, it is
+	 * impossible to get a tainted instruction; for such kprobes
+	 * registered after ftrace ready, it will use
+	 * arm_kprobe_ftrace() and won't get here.
+	 */
+	return addr;
 }
 
 /* Check if paddr is at an instruction boundary */
-- 
1.8.4

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