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b=RFI9/4lWpb0pVGNGuf28Wr3/bXq0ZZDrEnPzoHLgEsJX6u4e6iZ+XEJGBQx/Okbv4 RvagSutQEl3DkodugTgFoGzvIx9v9EHuTAcuMzkJUic9q3i8kduH2bJHX8dJL4iXZ4 KWQJoclVvLzlCG9J2fZmGBB1UZ/xm9N/oIlkkXEg= Date: Wed, 22 May 2024 16:23:24 -0700 From: Andrew Morton To: Jeff Xu Cc: =?UTF-8?B?QmFybmFiw6FzIFDFkWN6ZQ==?= , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com, jorgelo@chromium.org, skhan@linuxfoundation.org, keescook@chromium.org Subject: Re: [PATCH v1] memfd: `MFD_NOEXEC_SEAL` should not imply `MFD_ALLOW_SEALING` Message-Id: <20240522162324.0aeba086228eddd8aff4f628@linux-foundation.org> In-Reply-To: References: <20240513191544.94754-1-pobrn@protonmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: zmm1amgowwm5kjoxn8ub8kunf6irndbg X-Rspamd-Queue-Id: 95F7818000F X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1716420209-236615 X-HE-Meta: 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 16MBh3Xx 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 15 May 2024 23:11:12 -0700 Jeff Xu wrote: > On Mon, May 13, 2024 at 12:15 PM Barnabás Pőcze wrote: > > > > `MFD_NOEXEC_SEAL` should remove the executable bits and set > > `F_SEAL_EXEC` to prevent further modifications to the executable > > bits as per the comment in the uapi header file: > > > > not executable and sealed to prevent changing to executable > > > > However, currently, it also unsets `F_SEAL_SEAL`, essentially > > acting as a superset of `MFD_ALLOW_SEALING`. Nothing implies > > that it should be so, and indeed up until the second version > > of the of the patchset[0] that introduced `MFD_EXEC` and > > `MFD_NOEXEC_SEAL`, `F_SEAL_SEAL` was not removed, however it > > was changed in the third revision of the patchset[1] without > > a clear explanation. > > > > This behaviour is suprising for application developers, > > there is no documentation that would reveal that `MFD_NOEXEC_SEAL` > > has the additional effect of `MFD_ALLOW_SEALING`. > > > Ya, I agree that there should be documentation, such as a man page. I will > work on that. > > > So do not remove `F_SEAL_SEAL` when `MFD_NOEXEC_SEAL` is requested. > > This is technically an ABI break, but it seems very unlikely that an > > application would depend on this behaviour (unless by accident). > > > > [0]: https://lore.kernel.org/lkml/20220805222126.142525-3-jeffxu@google.com/ > > [1]: https://lore.kernel.org/lkml/20221202013404.163143-3-jeffxu@google.com/ > > ... > > Reviewed-by: Jeff Xu It's a change to a userspace API, yes? Please let's have a detailed description of why this is OK. Why it won't affect any existing users. Also, please let's give consideration to a -stable backport so that all kernel versions will eventually behave in the same manner.