linux-kernel - Re: [PATCH v7 2/4] uaccess: always export _copy_[from|to]_user with CONFIG

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Message-Id: <de6cb179-b21f-4e2d-a329-da5c4a138878@app.fastmail.com>
Date: Sun, 22 Sep 2024 07:52:34 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Sasha Levin" <sashal@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Tariq Toukan" <tariqt@...dia.com>, linux-rdma@...r.kernel.org
Cc: "Miguel Ojeda" <ojeda@...nel.org>, "Matthew Wilcox" <willy@...radead.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Kees Cook" <keescook@...omium.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>,
 "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>, "Trevor Gross" <tmgross@...ch.edu>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, "Christian Brauner" <brauner@...nel.org>
Subject: Re: [PATCH v7 2/4] uaccess: always export _copy_[from|to]_user with
 CONFIG_RUST

On Sun, Sep 22, 2024, at 07:08, Sasha Levin wrote:
> On Tue, May 28, 2024 at 02:58:03PM +0000, Alice Ryhl wrote:
>>From: Arnd Bergmann <arnd@...db.de>
>>
>>Rust code needs to be able to access _copy_from_user and _copy_to_user
>>so that it can skip the check_copy_size check in cases where the length
>>is known at compile-time, mirroring the logic for when C code will skip
>>check_copy_size. To do this, we ensure that exported versions of these
>>methods are available when CONFIG_RUST is enabled.
>>
>>Alice has verified that this patch passes the CONFIG_TEST_USER_COPY test
>>on x86 using the Android cuttlefish emulator.
>
> Hi folks,
>
> I've noticed a build failure using GCC 9.5.0 on arm64 allmodconfig
> builds:
>
> In file included from ./arch/arm64/include/asm/preempt.h:6,
>                   from ./include/linux/preempt.h:79,
>                   from ./include/linux/alloc_tag.h:11,
>                   from ./include/linux/percpu.h:5,
>                   from ./include/linux/context_tracking_state.h:5,
>                   from ./include/linux/hardirq.h:5,
>                   from drivers/net/ethernet/mellanox/mlx4/cq.c:37:
> In function 'check_copy_size',
>      inlined from 'mlx4_init_user_cqes' at 
> ./include/linux/uaccess.h:203:7:
> ./include/linux/thread_info.h:244:4: error: call to '__bad_copy_from' 
> declared with attribute error: copy source size is too small
>    244 |    __bad_copy_from();
>        |    ^~~~~~~~~~~~~~~~~
> make[7]: *** [scripts/Makefile.build:244: 
> drivers/net/ethernet/mellanox/mlx4/cq.o] Error 1
>
> I do not have CONFIG_RUST enabled in those builds.
>
> I've bisected the issue (twice!) and bisection points to this patch
> which landed upstream as 1f9a8286bc0c ("uaccess: always export
> _copy_[from|to]_user with CONFIG_RUST").
>
> Reverting said commit on top of Linus's tree fixes the build breakage.

Right, it seems we still need the fix I posted in

https://lore.kernel.org/lkml/20230418114730.3674657-1-arnd@kernel.org/

Tariq, should I resend this with your Reviewed-by, or can you
apply it from the old version and make sure it finds its way
into mainline and 6.11?

     Arnd