Re: Crash when attaching uretprobes to processes running in Docker

[Google]

On Tue, 14 Jan 2025 15:21:29 +0100
Jiri Olsa <olsajiri@xxxxxxxxx> wrote:

> On Tue, Jan 14, 2025 at 12:21:07PM +0100, Oleg Nesterov wrote:
> > On 01/14, Masami Hiramatsu wrote:
> > >
> > > On Tue, 14 Jan 2025 10:22:20 +0100
> > > Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
> > >
> > > > @@ -418,6 +439,9 @@ SYSCALL_DEFINE0(uretprobe)
> > > >  	regs->r11 = regs->flags;
> > > >  	regs->cx  = regs->ip;
> > > >
> > > > +	/* zero rbx to signal trampoline that uretprobe syscall was executed */
> > > > +	regs->bx  = 0;
> > >
> > > Can we just return -ENOSYS as like as other syscall instead of
> > > using rbx as a side channel?
> > > We can carefully check the return address is not -ERRNO when set up
> > > and reserve the -ENOSYS for this use case.
> > 
> > Not sure I understand...
> > 
> > But please not that the uretprobed function can return any value
> > including -ENOSYS, and this is what sys_uretprobe() has to return.
> 
> right, uretprobe syscall returns value of the uretprobed function,
> so we can't use any reserved value

We can make uretprobe (entry) fail if the return value is one of
errno or NULL, because it *knows* what the return value here.

Thank you,

> 
> jirka


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>