Re: Crash when attaching uretprobes to processes running in Docker

Jiri Olsa
2025-01-14T14:19:20Z

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

thanks,
jirka