linux-hardening - Re: [PATCH v10 1/5] mseal: Wire up mseal syscall

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Message-ID: <CABi2SkW+X4+m2odCHKVDzYYWPgvebxX_mr97NsKCRfkx641sHA@mail.gmail.com>
Date: Mon, 15 Apr 2024 12:06:24 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>, akpm@...ux-foundation.org, 
	keescook@...omium.org, jannh@...gle.com, sroettger@...gle.com, 
	willy@...radead.org, gregkh@...uxfoundation.org, corbet@....net, 
	Liam.Howlett@...cle.com, surenb@...gle.com, merimus@...gle.com, 
	rdunlap@...radead.org, jeffxu@...gle.com, jorgelo@...omium.org, 
	groeck@...omium.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org, pedro.falcato@...il.com, 
	dave.hansen@...el.com, linux-hardening@...r.kernel.org, deraadt@...nbsd.org
Subject: Re: [PATCH v10 1/5] mseal: Wire up mseal syscall

On Mon, Apr 15, 2024 at 11:21 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Mon, 15 Apr 2024 at 11:11, Muhammad Usama Anjum
> <usama.anjum@...labora.com> wrote:
> >
> > It isn't logical to wire up something which isn't present
>
> Actually, with system calls, the rules end up being almost opposite.
>
> There's no point in adding the code if it's not reachable. So adding
> the system call code before adding the wiring makes no sense.
>
> So you have two cases: add the stubs first, or add the code first.
> Neither does anything without the other.
>
> So then you go "add both in the same commit" option, which ends up
> being horrible from a "review the code" standpoint. The two parts are
> entirely different and mixing them up makes the patch very unclear
> (and has very different target audiences for reviewing it - the MM
> people really shouldn't have to look at the architecture wiring
> parts).
>
> End result: there are no "this is the logical ordering" cases.
>
> But the "wire up system calls" part actually has some reasons to be first:
>
>  - it reserves the system call number
>
>  - it adds the "when system call isn't enabled, return -ENOSYS"
> conditional system call logic
>
> so I actually tend prefer this ordering when it comes to system calls.
>
I confirm that the wire up change can be merged by its own, i.e. build
will pass, and  -ENOSYS will be returned at runtime.

Thanks Linus for clarifying this.
-Jeff


>                 Linus