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

[Andy Lutomirski]

On Wed, Feb 12, 2025 at 2:04 PM Jiri Olsa <jolsa@xxxxxxxxxx> 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