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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 24 Aug 2020 17:32:35 -0700
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Subject: Re: [PATCH v11 9/9] x86: Disallow vsyscall emulation when CET is enabled
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
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On Mon, Aug 24, 2020 at 5:30 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> From: "H.J. Lu" <hjl.tools@gmail.com>
>
> Emulation of the legacy vsyscall page is required by some programs built
> before 2013.  Newer programs after 2013 don't use it.  Disallow vsyscall
> emulation when Control-flow Enforcement (CET) is enabled to enhance
> security.

NAK.

By all means disable execute emulation if CET-IBT is enabled at the
time emulation is attempted, and maybe even disable the vsyscall page
entirely if you can magically tell that CET-IBT will be enabled when a
process starts, but you don't get to just disable it outright on a
CET-enabled kernel.