Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

Eyal Birger
2025-01-17T13:36:46Z

On Fri, Jan 17, 2025 at 12:02 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Fri, 17 Jan 2025 02:39:28 +0100
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> > On 01/16, Eyal Birger wrote:
> > >
> > > Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> > > Reported-by: Rafael Buchbinder <rafi@rbk.io>
> > > Link: https://lore.kernel.org/lkml/CAHsH6Gs3Eh8DFU0wq58c_LF8A4_+o6z456J7BidmcVY2AqOnHQ@mail.gmail.com/
> > > Cc: stable@vger.kernel.org
> > ...
> > > @@ -1359,6 +1359,11 @@ int __secure_computing(const struct seccomp_data *sd)
> > > this_syscall = sd ? sd->nr :
> > > syscall_get_nr(current, current_pt_regs());
> > >
> > > +#ifdef CONFIG_X86_64
> > > + if (unlikely(this_syscall == __NR_uretprobe) && !in_ia32_syscall())
> > > + return 0;
> > > +#endif
> >
> > Acked-by: Oleg Nesterov <oleg@redhat.com>
> >
> >
> > A note for the seccomp maintainers...
> >
> > I don't know what do you think, but I agree in advance that the very fact this
> > patch adds "#ifdef CONFIG_X86_64" into __secure_computing() doesn't look nice.
> >
>
> Indeed. in_ia32_syscall() depends arch/x86 too.
> We can add an inline function like;
>
> ``` uprobes.h
> static inline bool is_uprobe_syscall(int syscall)
> {
> // arch_is_uprobe_syscall check can be replaced by Kconfig,
> // something like CONFIG_ARCH_URETPROBE_SYSCALL.
> #ifdef arch_is_uprobe_syscall
> return arch_is_uprobe_syscall(syscall)
> #else
> return false;
> #endif
> }
> ```
> and
> ``` arch/x86/include/asm/uprobes.h
> #define arch_is_uprobe_syscall(syscall) \
> (IS_ENABLED(CONFIG_X86_64) && syscall == __NR_uretprobe && !in_ia32_syscall())
> ```

Notice it'll need to be enclosed in ifdef CONFIG_X86_64 as __NR_uretprobe
isn't defined otherwise so the IS_ENABLED isn't needed.

>
> > The problem is that we need a simple patch for -stable which fixes the real
> > problem. We can cleanup this logic later, I think.
>
> Hmm, at least we should make it is_uprobe_syscall() in uprobes.h so that
> do not pollute the seccomp subsystem with #ifdef.

I like this approach.

Notice it does add a couple of includes that weren't there before:
- arch/x86/include/asm/uprobes.h would include asm/unistd.h
- seccomp.c would include linux/uprobes.h

So it's a less "trivial" patch... If that's ok I can repost with these
changes.

Eyal.