Re: Crash when attaching uretprobes to processes running in Docker

[Andrii Nakryiko]

On Tue, Jan 14, 2025 at 6:19 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Tue, Jan 14, 2025 at 11:58:03AM +0100, Oleg Nesterov wrote:
> > On 01/14, Jiri Olsa wrote:
> > >
> > > --- a/arch/x86/kernel/uprobes.c
> > > +++ b/arch/x86/kernel/uprobes.c
> > > @@ -315,14 +315,25 @@ asm (
> > >     ".global uretprobe_trampoline_entry\n"
> > >     "uretprobe_trampoline_entry:\n"
> > >     "pushq %rax\n"
> > > +   "pushq %rbx\n"
> > >     "pushq %rcx\n"
> > >     "pushq %r11\n"
> > > +   "movq $1, %rbx\n"
> > >     "movq $" __stringify(__NR_uretprobe) ", %rax\n"
> > >     "syscall\n"
> > >     ".global uretprobe_syscall_check\n"
> > >     "uretprobe_syscall_check:\n"
> > > +   "or %rbx,%rbx\n"
> > > +   "jz uretprobe_syscall_return\n"
> > >     "popq %r11\n"
> > >     "popq %rcx\n"
> > > +   "popq %rbx\n"
> > > +   "popq %rax\n"
> > > +   "int3\n"
> > > +   "uretprobe_syscall_return:\n"
> > > +   "popq %r11\n"
> > > +   "popq %rcx\n"
> > > +   "popq %rbx\n"
> >
> > But why do we need to abuse %rbx? Can't uretprobe_trampoline_entry do
> >
> >       syscall
> >
> > // int3_section, in case sys_uretprobe() doesn't work
> >       popq %r11
> >       popq %rcx
> >       popq %rax
> >       int3
> >
> > uretprobe_syscall_return:
> >       popq %r11
> >       popq %rcx
> >       popq %rbx
> >       retq
> >
> > and change sys_uretprobe() to do
> >
> >       - regs->ip = ip;
> >       + regs->ip = ip + sizeof(int3_section);
>
> nice idea, I wonder we get the trampoline size under one xol slot with that
>

Should we just fix whoever is blocking kernel-internal special syscall
(sys_uretprobe)? What would happen if someone blocked that other
special kernel-internal syscall for signal handling (can't remember
the name, but the one that was an inspiration/justification for
sys_uretprobe)?


> thanks,
> jirka