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Date: Tue, 12 Jan 2021 06:15:39 +0000 From: "Bae, Chang Seok" <chang.seok.bae@...el.com> To: "Lutomirski, Andy" <luto@...capital.net> CC: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, "tdevries@...e.com" <tdevries@...e.com>, x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>, "Metzger, Markus T" <markus.t.metzger@...el.com> Subject: Re: gdbserver + fsgsbase kaputt > On Jan 11, 2021, at 13:06, Andy Lutomirski <luto@...capital.net> wrote: > >> On Jan 11, 2021, at 12:00 PM, Borislav Petkov <bp@...en8.de> 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. I was able to find this patch in that way: commit 0bf7e460361c703333f3a82e50e7871465fe20f9 Author: Andy Lutomirski <luto@...nel.org> Date: Thu May 28 16:13:51 2020 -0400 x86/process/64: Use FSBSBASE in switch_to() if available The GDB behavior looks to be different between the two cases -- with vs without gdb server, when I checked the GS/GSBASE values on the ptrace front. It set the correct GSBASE (e.g.,=0xf7fcf0c0) of GS=0x63 without running the server. But GSBASE=0 with the server. When I forced to set the correct base, it exited normally. Thanks, Chang
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