linux-kernel - Re: [PATCH 2/3] rust: add typed accessors for userspace pointers

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Message-Id: <070574cb-8d7f-4fe7-9826-cec6110168ff@app.fastmail.com>
Date: Thu, 25 Jan 2024 13:26:50 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Alice Ryhl" <aliceryhl@...gle.com>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Alex Gaynor" <alex.gaynor@...il.com>,
 "Wedson Almeida Filho" <wedsonaf@...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@...sung.com>,
 "Kees Cook" <keescook@...omium.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Andrew Morton" <akpm@...ux-foundation.org>
Cc: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 Arve Hjønnevåg <arve@...roid.com>,
 "Todd Kjos" <tkjos@...roid.com>, "Martijn Coenen" <maco@...roid.com>,
 "Joel Fernandes" <joel@...lfernandes.org>,
 "Carlos Llamas" <cmllamas@...gle.com>,
 "Suren Baghdasaryan" <surenb@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 "Christian Brauner" <brauner@...nel.org>
Subject: Re: [PATCH 2/3] rust: add typed accessors for userspace pointers

On Wed, Jan 24, 2024, at 12:20, Alice Ryhl wrote:
> +unsigned long 
> rust_helper_copy_from_user_unsafe_skip_check_object_size(void *to, 
> const void __user *from, unsigned long n)
> +{
> +	unsigned long res;
> +
> +	might_fault();
> +	instrument_copy_from_user_before(to, from, n);
> +	if (should_fail_usercopy())
> +		return n;
> +	res = raw_copy_from_user(to, from, n);
> +	instrument_copy_from_user_after(to, from, n, res);
> +	return res;
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_copy_from_user_unsafe_skip_check_object_size);
> +
> +unsigned long 
> rust_helper_copy_to_user_unsafe_skip_check_object_size(void __user *to, 
> const void *from, unsigned long n)
> +{
> +	might_fault();
> +	if (should_fail_usercopy())
> +		return n;
> +	instrument_copy_to_user(to, from, n);
> +	return raw_copy_to_user(to, from, n);
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_copy_to_user_unsafe_skip_check_object_size);

These functions are almost identical to the ones in
lib/usercopy.c for !defined(INLINE_COPY_TO_USER).

That version has an extra memset() after a partial
copy_from_user(), and you probably want to have the
same thing here for consistency.

I think ideally we should only have one out-of-line copy
of these two functions and have that one shared between
rust and architectures that want the C version out of line
as well.

     Arnd