kprobes/x86: Do not modify singlestep buffer while resuming

Do not modify singlestep execution buffer (kprobe.ainsn.insn)
while resuming from single-stepping, instead, modifies
the buffer to add a jump back instruction at preparing
buffer.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ye Xiaolong <xiaolong.ye@intel.com>
Link: http://lkml.kernel.org/r/149076361560.22469.1610155860343077495.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 20 insertions, 22 deletions

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6327f95832a0..a654054eae7e 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -399,23 +399,36 @@ int __copy_instruction(u8 *dest, u8 *src)
         return length;
 }
 
+/* Prepare reljump right after instruction to boost */
+static void prepare_boost(struct kprobe *p, int length)
+{
+        if (can_boost(p->ainsn.insn, p->addr) &&
+            MAX_INSN_SIZE - length >= RELATIVEJUMP_SIZE) {
+                /*
+                 * These instructions can be executed directly if it
+                 * jumps back to correct address.
+                 */
+                synthesize_reljump(p->ainsn.insn + length, p->addr + length);
+                p->ainsn.boostable = 1;
+        } else {
+                p->ainsn.boostable = -1;
+        }
+}
+
 static int arch_copy_kprobe(struct kprobe *p)
 {
-        int ret;
+        int len;
 
         /* Copy an instruction with recovering if other optprobe modifies it.*/
-        ret = __copy_instruction(p->ainsn.insn, p->addr);
-        if (!ret)
+        len = __copy_instruction(p->ainsn.insn, p->addr);
+        if (!len)
                 return -EINVAL;
 
         /*
          * __copy_instruction can modify the displacement of the instruction,
          * but it doesn't affect boostable check.
          */
-        if (can_boost(p->ainsn.insn, p->addr))
-                p->ainsn.boostable = 0;
-        else
-                p->ainsn.boostable = -1;
+        prepare_boost(p, len);
 
         /* Check whether the instruction modifies Interrupt Flag or not */
         p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn);
@@ -878,21 +891,6 @@ static void resume_execution(struct kprobe *p, struct pt_regs *regs,
                 break;
         }
 
-        if (p->ainsn.boostable == 0) {
-                if ((regs->ip > copy_ip) &&
-                    (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) {
-                        /*
-                         * These instructions can be executed directly if it
-                         * jumps back to correct address.
-                         */
-                        synthesize_reljump((void *)regs->ip,
-                                (void *)orig_ip + (regs->ip - copy_ip));
-                        p->ainsn.boostable = 1;
-                } else {
-                        p->ainsn.boostable = -1;
-                }
-        }
-
         regs->ip += orig_ip - copy_ip;
 
 no_change: