linux-kernel - Re: [PATCH v3 2/2] rust: page: Extend support to existing struct page mappings

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: <f0052c1d-ce36-447c-af1f-db12940f6cc1@gmail.com>
Date: Fri, 22 Nov 2024 10:36:39 +0200
From: Abdiel Janulgue <abdiel.janulgue@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>, Jann Horn <jannh@...gle.com>
Cc: rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
 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>,
 Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>, Wedson Almeida Filho
 <wedsonaf@...il.com>, Valentin Obst <kernel@...entinobst.de>,
 open list <linux-kernel@...r.kernel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>, airlied@...hat.com
Subject: Re: [PATCH v3 2/2] rust: page: Extend support to existing struct page
 mappings

On 22/11/2024 09:55, Alice Ryhl wrote:
> On Thu, Nov 21, 2024 at 9:18 PM Jann Horn <jannh@...gle.com> wrote:
>>
>> On Wed, Nov 20, 2024 at 11:56 PM Abdiel Janulgue
>> <abdiel.janulgue@...il.com> wrote:
>>> On 19/11/2024 19:07, Jann Horn wrote:
>>>>> +    pub fn page_slice_to_page<'a>(page: &PageSlice) -> Result<&'a Self>
>>>>
>>>> Sorry, can you explain to me what the semantics of this are? Does this
>>>> create a Page reference that is not lifetime-bound to the PageSlice?
>>>
>>> This creates a Page reference that is tied to the lifetime of the `C
>>> struct page` behind the PageSlice buffer. Basically, it's just a cast
>>> from the struct page pointer and does not own that resource.
>>
>> How is the Page reference tied to the lifetime of the C "struct page"?
>>
>> I asked some Rust experts to explain to me what this method signature
>> expands to, and they added the following to the Rust docs:
>>
>> https://github.com/rust-lang/reference/blob/master/src/lifetime-elision.md
>> ```
>> fn other_args1<'a>(arg: &str) -> &'a str;             // elided
>> fn other_args2<'a, 'b>(arg: &'b str) -> &'a str;      // expanded
>> ```
>>
>> Basically, my understanding is that since you are explicitly
>> specifying that the result should have lifetime 'a, but you are not
>> specifying the lifetime of the parameter, the parameter is given a
>> separate, unrelated lifetime by the compiler? Am I misunderstanding
>> how this works, or is that a typo in the method signature?
> 
> No, you are correct. The signature is wrong and lets the caller pick
> any lifetime they want, with no relation to the lifetime of the
> underlying `struct page`.

But that could be put in the invariant that the PageSlice buffer must 
last at least the lifetime `'a`?

> 
>  From a C perspective, what are the lifetime requirements of vmalloc_to_page?
> 

If I'm not mistaken, that should be the lifetime of the vmalloc'd buffer 
right?