FAILED: patch "[PATCH] memfd: improve userspace warnings for missing exec-related" failed to apply to 6.4-stable tree

The patch below does not apply to the 6.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.4.y
git checkout FETCH_HEAD
git cherry-pick -x 434ed3350f57c03a9654fe0619755cc137a58935
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023090742-velocity-perjury-fa80@gregkh' --subject-prefix 'PATCH 6.4.y' HEAD^..

Possible dependencies:

434ed3350f57 ("memfd: improve userspace warnings for missing exec-related flags") 202e14222fad ("memfd: do not -EACCES old memfd_create() users with vm.memfd_noexec=2") badbbcd76545 ("selftests/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED") 72de25913022 ("mm/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 434ed3350f57c03a9654fe0619755cc137a58935 Mon Sep 17 00:00:00 2001
From: Aleksa Sarai <[email protected]>
Date: Mon, 14 Aug 2023 18:40:59 +1000
Subject: [PATCH] memfd: improve userspace warnings for missing exec-related
flags

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/[email protected]/
[2]: https://lore.kernel.org/202212161233.85C9783FB@keescook/
[3]: https://lore.kernel.org/Y5yS8wCnuYGLHMj4@x1n/
[4]: https://lore.kernel.org/[email protected]/

index d65485c762de..aa46521057ab 100644
@@ -315,7 +315,7 @@ SYSCALL_DEFINE2(memfd_create,
 		return -EINVAL;
 
 	if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
-		pr_warn_once(
+		pr_info_ratelimited(
 			"%s[%d]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set\n",
 			current->comm, task_pid_nr(current));
 	}