linux-kernel - Re: [PATCH 2/4] mm: perform VMA allocation, freeing, duplication in mm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJuCfpHxWwEiZdX-xrxe7J+Q20otPTPs4NR-oJBSnL7HNt-f2A@mail.gmail.com>
Date: Thu, 24 Apr 2025 18:37:39 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>, 
	Pedro Falcato <pfalcato@...e.de>, Kees Cook <kees@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm: perform VMA allocation, freeing, duplication in mm

On Thu, Apr 24, 2025 at 6:22 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Thu, Apr 24, 2025 at 2:22 PM David Hildenbrand <david@...hat.com> wrote:
> >
> > On 24.04.25 23:15, Lorenzo Stoakes wrote:
> > > Right now these are performed in kernel/fork.c which is odd and a violation
> > > of separation of concerns, as well as preventing us from integrating this
> > > and related logic into userland VMA testing going forward, and perhaps more
> > > importantly - enabling us to, in a subsequent commit, make VMA
> > > allocation/freeing a purely internal mm operation.
> > >
> > > There is a fly in the ointment - nommu - mmap.c is not compiled if
> > > CONFIG_MMU is not set, and there is no sensible place to put these outside
> > > of that, so we are put in the position of having to duplication some logic
>
> s/to duplication/to duplicate
>
> > > here.
> > >
> > > This isn't ideal, but since nommu is a niche use-case, already duplicates a
> > > great deal of mmu logic by its nature and we can eliminate code that is not
> > > applicable to nommu, it seems a worthwhile trade-off.
> > >
> > > The intent is to move all this logic to vma.c in a subsequent commit,
> > > rendering VMA allocation, freeing and duplication mm-internal-only and
> > > userland testable.
> >
> > I'm pretty sure you tried it, but what's the big blocker to have patch
> > #3 first, so we can avoid the temporary move of the code to mmap.c ?
>
> Completely agree with David.
> I peeked into 4/4 and it seems you want to keep vma.c completely
> CONFIG_MMU-centric. I know we treat NOMMU as an unwanted child but
> IMHO it would be much cleaner to move these functions into vma.c from
> the beginning and have an #ifdef CONFIG_MMU there like this:
>
> mm/vma.c
>
> /* Functions identical for MMU/NOMMU */
> struct vm_area_struct *vm_area_alloc(struct mm_struct *mm) {...}
> void __init vma_state_init(void) {...}
>
> #ifdef CONFIG_MMU
> static void vm_area_init_from(const struct vm_area_struct *src,
>                              struct vm_area_struct *dest) {...}
> struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) {...}
> void vm_area_free(struct vm_area_struct *vma) {...}
> #else /* CONFIG_MMU */
> static void vm_area_init_from(const struct vm_area_struct *src,
>                              struct vm_area_struct *dest) {...}
> struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) {...}
> void vm_area_free(struct vm_area_struct *vma) {...}
> #endif /* CONFIG_MMU */

3/4 and 4/4 look reasonable but they can change substantially
depending on your answer to my suggestion above, so I'll wait for your
answer before moving forward.
Thanks for doing this!
Suren.

>
>
>
>
>
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >