Re: Crash when attaching uretprobes to processes running in Docker

[Jiri Olsa]

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