2 files changed, 42 insertions, 14 deletions

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6a1146ea4d4d..4e3d5a9621fe 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -223,27 +223,48 @@ static unsigned long
 __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
 {
         struct kprobe *kp;
+        unsigned long faddr;
 
         kp = get_kprobe((void *)addr);
-        /* There is no probe, return original address */
-        if (!kp)
+        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.
+         * 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, 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.
+         * 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, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
-        buf[0] = kp->opcode;
+        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;
 }
 
@@ -251,6 +272,7 @@ __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.
  */
 unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
 {
@@ -285,6 +307,8 @@ static int can_probe(unsigned long paddr)
                  * normally used, we just go through if there is no kprobe.
                  */
                 __addr = recover_probed_instruction(buf, addr);
+                if (!__addr)
+                        return 0;
                 kernel_insn_init(&insn, (void *)__addr, MAX_INSN_SIZE);
                 insn_get_length(&insn);
 
@@ -333,6 +357,8 @@ int __copy_instruction(u8 *dest, u8 *src)
         unsigned long recovered_insn =
                 recover_probed_instruction(buf, (unsigned long)src);
 
+        if (!recovered_insn)
+                return 0;
         kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
         insn_get_length(&insn);
         /* Another subsystem puts a breakpoint, failed to recover */
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 0dd8d089c315..7b3b9d15c47a 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -259,6 +259,8 @@ static int can_optimize(unsigned long paddr)
                          */
                         return 0;
                 recovered_insn = recover_probed_instruction(buf, addr);
+                if (!recovered_insn)
+                        return 0;
                 kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
                 insn_get_length(&insn);
                 /* Another subsystem puts a breakpoint */