6.4-stable review patch. If anyone has any objections, please let me know.
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From: Aleksa Sarai cyphar@cyphar.com
[ Upstream commit 434ed3350f57c03a9654fe0619755cc137a58935 ]
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@google.com/ [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@linuxfoundation...
Link: https://lkml.kernel.org/r/20230814-memfd-vm-noexec-uapi-fixes-v2-3-7ff9e3e10... Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC") Signed-off-by: Aleksa Sarai cyphar@cyphar.com Cc: Christian Brauner brauner@kernel.org Cc: Daniel Verkamp dverkamp@chromium.org Cc: Dominique Martinet asmadeus@codewreck.org Cc: Kees Cook keescook@chromium.org Cc: Shuah Khan shuah@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/memfd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memfd.c b/mm/memfd.c index d65485c762def..aa46521057ab1 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -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)); }