1 files changed, 73 insertions, 0 deletions

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d2b000..aa15f3e1f64b 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -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 +246,75 @@ 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;
+
+        /*
+         *  Basically, kp->ainsn.insn has an original instruction.
+         *  However, RIP-relative instruction can not do single-stepping
+         *  at different place, fix_riprel() 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.
+         */
+        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];
+
+        if (!kallsyms_lookup(paddr, NULL, &offset, NULL, __dummy_buf))
+                return 0;
+
+        /* Decode instructions */
+        addr = paddr - offset;
+        while (addr < paddr) {
+                kernel_insn_init(&insn, (void *)addr);
+                insn_get_opcode(&insn);
+
+                /*
+                 * Check if the instruction has been modified by another
+                 * kprobe, in which case we replace the breakpoint by the
+                 * original instruction in our buffer.
+                 */
+                if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) {
+                        ret = recover_probed_instruction(buf, addr);
+                        if (ret)
+                                /*
+                                 * Another debugging subsystem might insert
+                                 * this breakpoint. In that case, we can't
+                                 * recover it.
+                                 */
+                                return 0;
+                        kernel_insn_init(&insn, buf);
+                }
+                insn_get_length(&insn);
+                addr += insn.length;
+        }
+
+        return (addr == paddr);
+}
+
 /*
  * Returns non-zero if opcode modifies the interrupt flag.
  */
@@ -359,6 +430,8 @@ 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)