linux-kernel - Re: [PATCH v2 23/39] x86: Introduce userspace API for CET enabling

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Date:   Mon, 10 Oct 2022 16:28:57 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "fweimer@...hat.com" <fweimer@...hat.com>
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Subject: Re: [PATCH v2 23/39] x86: Introduce userspace API for CET enabling

On Mon, 2022-10-10 at 12:56 +0200, Florian Weimer wrote:
> > +     /* Only support enabling/disabling one feature at a time. */
> > +     if (hweight_long(features) > 1)
> > +             return -EINVAL;
> 
> This means we'll soon need three extra system calls for x86-64
> process
> start: SHSTK, IBT, and switching off vsyscall emulation.  (The latter
> does not need any special CPU support.)
> 
> Maybe we can do something else instead to make the strace output a
> little bit cleaner?

In previous versions it supported enabling multiple features in a
single syscall. Thomas Gleixner pointed out that (this was on the LAM
patchset that shared the interface at the time) it makes the behavior
of what to do when one feature fails to enable complicated:

https://lore.kernel.org/lkml/87zgjjqico.ffs@tglx/