Re: gdbserver + fsgsbase kaputt

[Andy Lutomirski]

On Mon, Jan 11, 2021 at 1:06 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
>
> > On Jan 11, 2021, at 12:00 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> >
>
>
> > Or do you mean I should add "unsafe_fsgsbase" to grub cmdline and bisect
> > with fsgsbase enabled in all test kernels?
>
> Yes. But I can also look myself in a bit.
>

Tom, if I reproduce it in an interactive gdb and play a bit, I get:

Program received signal SIGSEGV, Segmentation fault.
0xf7df2cb6 in init_cacheinfo () from target:/lib/libc.so.6
(gdb) p $gs = $gs
$1 = 99
(gdb) si

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.

That's gdb itself crashing.  Any idea what's wrong?