linux-kernel - Re: [PATCHv3 perf/core] uprobes: Harden uretprobe syscall trampoline check

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Message-ID: <CALCETrVFdAFVinbpPK+q7pSQHo3=JgGxZSPZVz-y7oaG=xP3fA@mail.gmail.com>
Date: Wed, 12 Feb 2025 17:37:11 -0800
From: Andy Lutomirski <luto@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Kees Cook <kees@...nel.org>, Eyal Birger <eyal.birger@...il.com>, 
	stable@...r.kernel.org, Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-api@...r.kernel.org, x86@...nel.org, 
	bpf@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Andy Lutomirski <luto@...nel.org>, Deepak Gupta <debug@...osinc.com>, 
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCHv3 perf/core] uprobes: Harden uretprobe syscall trampoline check

On Wed, Feb 12, 2025 at 2:04 PM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Jann reported [1] possible issue when trampoline_check_ip returns
> address near the bottom of the address space that is allowed to
> call into the syscall if uretprobes are not set up.
>
> Though the mmap minimum address restrictions will typically prevent
> creating mappings there, let's make sure uretprobe syscall checks
> for that.

It would be a layering violation, but we could perhaps do better here:

> -       if (regs->ip != trampoline_check_ip())
> +       /* Make sure the ip matches the only allowed sys_uretprobe caller. */
> +       if (unlikely(regs->ip != trampoline_check_ip(tramp)))
>                 goto sigill;

Instead of SIGILL, perhaps this should do the seccomp action?  So the
logic in seccomp would be (sketchily, with some real mode1 mess):

if (is_a_real_uretprobe())
    skip seccomp;

where is_a_real_uretprobe() is only true if the nr and arch match
uretprobe *and* the address is right.

--Andy