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

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Feb 13, 2025 at 09:58:29AM -0800, Andy Lutomirski wrote:
> On Thu, Feb 13, 2025 at 1:16 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > 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?
> 
> The benefit would be that seccomp users that want to do something
> other than killing a process (returning an error code, getting
> notified, etc) could retain that functionality without the new
> automatic hole being poked for uretprobe() in cases where uprobes
> aren't in use or where the calling address doesn't match the uprobe
> trampoline.  IOW it would reduce the scope to which we're making
> seccomp behave unexpectedly.

Kees, any thoughts about this approach?

thanks,
jirka


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