Obviously not for inclusion yet ;) untested, lacks the comments, and I am not
sure it makes sense.
But I am wondering if this change can speedup uretprobes a bit more. Any chance
you can test it?
With 1/3 sys_uretprobe() changes regs->r11/cx, this is correct but implies iret.
See the /* SYSRET requires RCX == RIP and R11 == EFLAGS */ code in do_syscall_64().
With this patch uretprobe_syscall_entry restores rcx/r11 itself and does retq,
sys_uretprobe() needs to hijack regs->ip after uprobe_handle_trampoline() to
make it possible.
Comments?
Oleg.
---
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 069371e86180..b99f1d80a8c8 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -319,6 +319,9 @@ asm (
"pushq %r11\n"
"movq $462, %rax\n"
"syscall\n"
+ "popq %r11\n"
+ "popq %rcx\n"
+ "retq\n"
".global uretprobe_syscall_end\n"
"uretprobe_syscall_end:\n"
".popsection\n"
@@ -336,23 +339,20 @@ void *arch_uprobe_trampoline(unsigned long *psize)
SYSCALL_DEFINE0(uretprobe)
{
struct pt_regs *regs = task_pt_regs(current);
- unsigned long sregs[3], err;
+ unsigned long __user *ax_and_ret = (unsigned long __user *)regs->sp + 2;
+ unsigned long ip, err;
- /*
- * We set rax and syscall itself changes rcx and r11, so the syscall
- * trampoline saves their original values on stack. We need to read
- * them and set original register values and fix the rsp pointer back.
- */
- err = copy_from_user((void *) &sregs, (void *) regs->sp, sizeof(sregs));
- WARN_ON_ONCE(err);
-
- regs->r11 = sregs[0];
- regs->cx = sregs[1];
- regs->ax = sregs[2];
+ ip = regs->ip;
regs->orig_ax = -1;
- regs->sp += sizeof(sregs);
+ err = get_user(regs->ax, ax_and_ret);
+ WARN_ON_ONCE(err);
uprobe_handle_trampoline(regs);
+
+ err = put_user(regs->ip, ax_and_ret);
+ WARN_ON_ONCE(err);
+ regs->ip = ip;
+
return regs->ax;
}
