linux-kernel - Re: [PATCH] x86/mm: Do not verify W^X at boot up

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Date:   Tue, 25 Oct 2022 11:14:07 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH] x86/mm: Do not verify W^X at boot up

On Tue, Oct 25, 2022 at 10:48 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> mm_alloc() uses allocate_mm() which requires a kmem_cache to be set-up.

Well, that seems to be just a strange effect of mm_cachep being set up
by the oddly named "proc_caches_init" (I say oddly named because these
days I associate "proc" with proc-fs, but I think it actually comes
from "process").

That would actually probably make more sense if it was part of
mm_init(), much earlier (where we do "kmem_cache_init()")

So this is another oddity in how we do "mm_init()", but we haven't
actually initialized _that_ part of the mm setup.

Extra bonus points for another strange thing: we have "fork_init()",
but that too doesn't actually initialize the mm_cachep that fork()
actually uses. It does initialize the process one
(task_struct_cachep). So that kind of makes sense, but yeah, the
mm_alloc() cachep should have been set up by mm_init.

I think this is all "we just ended up randomly initializing things due
to hysterical raisins"

              Linus