Re: [PATCHv3 perf/core] uprobes: Harden uretprobe syscall trampoline check

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Feb 12, 2025 at 05:37:11PM -0800, Andy Lutomirski wrote:
> On Wed, Feb 12, 2025 at 2:04 PM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Jann reported [1] possible issue when trampoline_check_ip returns
> > address near the bottom of the address space that is allowed to
> > call into the syscall if uretprobes are not set up.
> >
> > Though the mmap minimum address restrictions will typically prevent
> > creating mappings there, let's make sure uretprobe syscall checks
> > for that.
> 
> It would be a layering violation, but we could perhaps do better here:
> 
> > -       if (regs->ip != trampoline_check_ip())
> > +       /* Make sure the ip matches the only allowed sys_uretprobe caller. */
> > +       if (unlikely(regs->ip != trampoline_check_ip(tramp)))
> >                 goto sigill;
> 
> Instead of SIGILL, perhaps this should do the seccomp action?  So the
> logic in seccomp would be (sketchily, with some real mode1 mess):
> 
> if (is_a_real_uretprobe())
>     skip seccomp;

IIUC you want to move the address check earlier to the seccomp path..
with the benefit that we would kill not allowed caller sooner?

jirka

> 
> where is_a_real_uretprobe() is only true if the nr and arch match
> uretprobe *and* the address is right.
> 
> --Andy