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Subject[RFC PATCH tip/master V2 4/8] kprobes/x86: Do not modify singlestep buffer while resuming
Date
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>
---
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..ea3b8e5 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((void *)p->ainsn.insn + length,
+ (void *)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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