linux-kernel - Re: [PATCH] x86/mm: Remove broken vsyscall emulation code from the page fault code

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Message-ID: <CAHk-=wiW=HyBNE2sx+rVyB2q+Xuuah+Ycp4o89+prgHUFHm_hQ@mail.gmail.com>
Date: Mon, 29 Apr 2024 17:05:38 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: Ingo Molnar <mingo@...nel.org>, Hillf Danton <hdanton@...a.com>, Peter Anvin <hpa@...or.com>, 
	Adrian Bunk <bunk@...nel.org>, 
	syzbot <syzbot+83e7f982ca045ab4405c@...kaller.appspotmail.com>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, andrii@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] x86/mm: Remove broken vsyscall emulation code from the
 page fault code

On Mon, 29 Apr 2024 at 16:30, Andy Lutomirski <luto@...capital.net> wrote:
>
> What strange page table handling do we do for XONLY?

Ahh, I misread set_vsyscall_pgtable_user_bits(). It's used for EMULATE
not for XONLY.

And the code in pti_setup_vsyscall() is just wrong, and does it for all cases.

> So I think we should remove EMULATE before removing XONLY.

Ok, looking at that again, I don't disagree. I misread that XONLY as
mapping it executable, but it is actually just mapping it readable

Yes, let's remove EMULATE, and keep XONLY.

           Linus