linux-kernel - Re: [PATCH v6 1/2] rust: mm: add abstractions for mm_struct and vm_area

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: <CAG48ez20pcWiHXCKWv74cw-CDjeMrO+kcbZtmsgRo=7+Yxzspg@mail.gmail.com>
Date: Fri, 8 Nov 2024 21:05:27 +0100
From: Jann Horn <jannh@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Matthew Wilcox <willy@...radead.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	John Hubbard <jhubbard@...dia.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Arnd Bergmann <arnd@...db.de>, Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	rust-for-linux@...r.kernel.org, Andreas Hindborg <a.hindborg@...nel.org>, 
	Wedson Almeida Filho <wedsonaf@...il.com>
Subject: Re: [PATCH v6 1/2] rust: mm: add abstractions for mm_struct and vm_area_struct

On Fri, Nov 8, 2024 at 8:01 PM Jann Horn <jannh@...gle.com> wrote:
> On Thu, Oct 10, 2024 at 2:56 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> > These abstractions allow you to manipulate vmas. Rust Binder will uses
> > these in a few different ways.
> >
> > In the mmap implementation, a VmAreaNew will be provided to the mmap
> > call which allows it to modify the vma in ways that are only okay during
> > initial setup. This is the case where the most methods are available.
> >
> > However, Rust Binder needs to insert and remove pages from the vma as
> > time passes. When incoming messages arrive, pages may need to be
> > inserted if space is missing, and in this case that is done by using a
> > stashed ARef<Mm> and calling mmget_not_zero followed by mmap_write_lock
> > followed by vma_lookup followed by vm_insert_page. In this case, since
> > mmap_write_lock is used, the VmAreaMut type will be in use.
>
> FYI, the way the C binder implementation uses vma_lookup() and
> vm_insert_page() is not very idiomatic. The standard way of
> implementing binder_alloc_free_page() would be to use something like
> unmap_mapping_range() instead of using
> vma_lookup()+zap_page_range_single(); though to set that up, you'd
> have to create one inode per binder file, maybe with something like
> the DRM subsystem's drm_fs_inode_new(). And instead of having
> binder_install_single_page(), the standard way would be to let
> binder_vm_fault() install PTEs lazily on fault. That way you'd never
> have to take mmap locks or grab MM references yourself.

Let me know if you think it would be helpful to see a prototype of
that in C - I think I can cobble that together, but doing it nicely
will require some work to convert at least some of the binder_alloc
locking to mutexes, and some more work to switch the ->f_mapping of
the binder file or something like that. (I guess modeling that in Rust
might be a bit of a pain though...)