linux-kernel - Re: Crash when attaching uretprobes to processes running in Docker

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Message-ID: <20250114105802.GA19816@redhat.com>
Date: Tue, 14 Jan 2025 11:58:03 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Aleksa Sarai <cyphar@...har.com>, Eyal Birger <eyal.birger@...il.com>,
	mhiramat@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>,
	linux-trace-kernel@...r.kernel.org,
	BPF-dev-list <bpf@...r.kernel.org>,
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>, peterz@...radead.org,
	tglx@...utronix.de, bp@...en8.de, x86@...nel.org,
	linux-api@...r.kernel.org, Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>, rafi@....io,
	Shmulik Ladkani <shmulik.ladkani@...il.com>
Subject: Re: Crash when attaching uretprobes to processes running in Docker

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.