On Wed, Mar 20, 2024 at 04:28:48PM +0100, Oleg Nesterov wrote:
SNIP
> SYSCALL_DEFINE0(uretprobe)
> {
> struct pt_regs *regs = task_pt_regs(current);
> unsigned long err, ip, sp, r11_cx_ax[3];
>
> err = copy_from_user(r11_cx_ax, (void __user*)regs->sp, sizeof(r11_cx_ax));
> WARN_ON_ONCE(err);
>
> // Q1: apart from ax, do we really care?
> // expose the "right" values of r11/cx/ax/sp to uprobe_consumer's
> regs->r11 = r11_cx_ax[0];
> regs->cx = r11_cx_ax[1];
> regs->ax = r11_cx_ax[2];
> regs->sp += sizeof(r11_cx_ax);
> regs->orig_ax = -1;
>
> ip = regs->ip;
> sp = regs->sp;
>
> uprobe_handle_trampoline(regs);
>
> // Q2: is it possible? do we care?
> // uprobe_consumer has changed sp, we can do nothing,
> // just return via iret.
> if (regs->sp != sp)
> return regs->ax;
> regs->sp -= sizeof(r11_cx_ax);
>
> // Q3: is it possible? do we care?
> // for the case uprobe_consumer has changed r11/cx
> r11_cx_ax[0] = regs->r11;
> r11_cx_ax[1] = regs->cx;
I wonder we could add test for this as well, and check we return
proper register values in case the consuer changed them, will check
>
> // comment to explain this hack
> r11_cx_ax[2] = regs->ip;
> regs->ip = ip;
we still need restore regs->ip in case do_syscall_64 decides to do
iret for some reason, right?
overall lgtm, thanks
jirka
>
> err = copy_to_user((void __user*)regs->sp, r11_cx_ax, sizeof(r11_cx_ax));
> WARN_ON_ONCE(err);
>
> // ensure sysret, see do_syscall_64()
> regs->r11 = regs->flags;
> regs->cx = regs->ip;
>
> return regs->ax;
> }
>
> Oleg.
>
