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

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Date: Mon, 15 Apr 2024 11:21:13 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: jeffxu@...omium.org, 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, 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.

                Linus