On Mon, Aug 14, 2023 at 06:40:59PM +1000, Aleksa Sarai wrote: > In order to incentivise userspace to switch to passing MFD_EXEC and > MFD_NOEXEC_SEAL, we need to provide a warning on each attempt to call > memfd_create() without the new flags. pr_warn_once() is not useful > because on most systems the one warning is burned up during the boot > process (on my system, systemd does this within the first second of > boot) and thus userspace will in practice never see the warnings to push > them to switch to the new flags. > > The original patchset[1] used pr_warn_ratelimited(), however there were > concerns about the degree of spam in the kernel log[2,3]. The resulting > inability to detect every case was flagged as an issue at the time[4]. > > While we could come up with an alternative rate-limiting scheme such as > only outputting the message if vm.memfd_noexec has been modified, or > only outputting the message once for a given task, these alternatives > have downsides that don't make sense given how low-stakes a single > kernel warning message is. Switching to pr_info_ratelimited() instead > should be fine -- it's possible some monitoring tool will be unhappy > with a stream of warning-level messages but there's already plenty of > info-level message spam in dmesg. > > [1]: https://lore.kernel.org/20221215001205.51969-4-jeffxu@xxxxxxxxxx/ > [2]: https://lore.kernel.org/202212161233.85C9783FB@keescook/ > [3]: https://lore.kernel.org/Y5yS8wCnuYGLHMj4@x1n/ > [4]: https://lore.kernel.org/f185bb42-b29c-977e-312e-3349eea15383@xxxxxxxxxxxxxxxxxxx/ > > Cc: stable@xxxxxxxxxxxxxxx # v6.3+ > Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC") > Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx> > --- Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
