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Subject[tip:perf/core] kprobes/x86: Do not modify singlestep buffer while resuming
Commit-ID:  804dec5bda9b4fcdab5f67fe61db4a0498af5221
Gitweb: http://git.kernel.org/tip/804dec5bda9b4fcdab5f67fe61db4a0498af5221
Author: Masami Hiramatsu <mhiramat@kernel.org>
AuthorDate: Wed, 29 Mar 2017 14:00:25 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 12 Apr 2017 09:23:45 +0200

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>
---
arch/x86/kernel/kprobes/core.c | 42 ++++++++++++++++++++----------------------
1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 6327f95..a654054 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;

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