Re: Crash when attaching uretprobes to processes running in Docker

[Oleg Nesterov <oleg@redhat.com>]

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);

?

Oleg.