linux-kernel - Re: [PATCH v3 00/16] Extended MODVERSIONS Support

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Message-ID: <CABCJKucPh3UA2JVn72B99T6xyTX+bs2o1G7WRXp__bx_zsecNg@mail.gmail.com>
Date: Thu, 15 Aug 2024 20:57:45 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Matthew Maurer <mmaurer@...gle.com>
Cc: masahiroy@...nel.org, ndesaulniers@...gle.com, ojeda@...nel.org, 
	gary@...yguo.net, mcgrof@...nel.org, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, rust-for-linux@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, neal@...pa.dev, 
	marcan@...can.st, j@...nau.net, asahi@...ts.linux.dev, 
	Boqun Feng <boqun.feng@...il.com>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Alice Ryhl <aliceryhl@...gle.com>
Subject: Re: [PATCH v3 00/16] Extended MODVERSIONS Support

Hi Matt,

On Tue, Aug 6, 2024 at 9:21 PM Matthew Maurer <mmaurer@...gle.com> wrote:
>
> Previously MODVERSIONS + RUST Redux [1]
>
> This patch series is intended for use alongside the Implement
> MODVERSIONS for RUST [2] series as a replacement for the symbol name
> hashing approach used there to enable RUST and MODVERSIONS at the same
> time.
>
> Elsewhere, we've seen a desire for long symbol name support for LTO
> symbol names [3], and the previous series came up [4] as a possible
> solution rather than hashing, which some have objected [5] to.
>
> This series adds a MODVERSIONS format which uses a section per column.
> This avoids userspace tools breaking if we need to make a similar change
> to the format in the future - we would do so by adding a new section,
> rather than editing the struct definition. In the new format, the name
> section is formatted as a concatenated sequence of NUL-terminated
> strings, which allows for arbitrary length names.
>
> Currently, this series emits both the extended format and the current
> format on all modules, and prefers the extended format when checking if
> present. I'm open to various other policies via Kconfig knobs, but this
> seemed like a good initial default.
>
> The refactor to MODVERSIONS is prefixed to this series as result of an
> explicit request [6] by Luis in response to the original patchset.
>
> If you are testing this patch alongside RUST by manually removing the
> !MODVERSIONS restriction (this series doesn't remove it, because the
> CRCs don't mean what we'd want them to yet, we need the DWARF patch for
> that) and have kernel hardening enabled, you may need the CPU
> Mitigations [7] series. Without it, the foo.mod.o file produced by the
> C compiler will reference __x86_return_thunk, but foo.o will not.
> This means that the version table will not contain a version for
> __x86_return_thunk, but foo.ko will reference it, which will result
> in a version check failure.

Thanks for reviving this series!

I tested your patches on top of my DWARF modversions series and it
seems to work as expected. I confirmed that Rust modules have
versions, the kernel verifies them correctly, loading the modules
succeeds, and scripts/export_report.pl seems to produce correct output
as well. Here's the tree I used, it includes the prerequisite patch
sets you mentioned:

https://github.com/samitolvanen/linux/commits/rustmodversions/

With the minor comments I had about patch 14 addressed:

Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com>
Tested-by: Sami Tolvanen <samitolvanen@...gle.com>

Sami