CVE-2024-50182 secretmem: disable memfd_secret() if arch cannot set direct map
Attackers can bypass memory secrecy protections on specific ARM64 configurations where direct map removal fails silently, exposing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-50182?
CVE-2024-50182 is a high-severity vulnerability in Linux kernel, published on 8 Nov 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
secretmem: disable memfd_secret() if arch cannot set direct map
Return -ENOSYS from memfd_secret() syscall if !can_set_direct_map(). This is the case for example on some arm64 configurations, where marking 4k PTEs in the direct map not present can only be done if the direct map is set up at 4k granularity in the first place (as ARM's break-before-make semantics do not easily allow breaking apart large/gigantic pages).
More precisely, on arm64 systems with !can_set_direct_map(), set_direct_map_invalid_noflush() is a no-op, however it returns success (0) instead of an error. This means that memfd_secret will seemingly "work" (e.g. syscall succeeds, you can mmap the fd and fault in pages), but it does not actually achieve its goal of removing its memory from the direct map.
Note that with this patch, memfd_secret() will start erroring on systems where can_set_direct_map() returns false (arm64 with CONFIG_RODATA_FULL_DEFAULT_ENABLED=n, CONFIG_DEBUG_PAGEALLOC=n and CONFIG_KFENCE=n), but that still seems better than the current silent failure. Since CONFIG_RODATA_FULL_DEFAULT_ENABLED defaults to 'y', most arm64 systems actually have a working memfd_secret() and aren't be affected.
From going through the iterations of the original memfd_secret patch series, it seems that disabling the syscall in these scenarios was the intended behavior [1] (preferred over having set_direct_map_invalid_noflush return an error as that would result in SIGBUSes at page-fault time), however the check for it got dropped between v16 [2] and v17 [3], when secretmem moved away from CMA allocations.
[1]: https://lore.kernel.org/lkml/[email protected]/ [2]: https://lore.kernel.org/lkml/[email protected]/#t [3]: https://lore.kernel.org/lkml/[email protected]/
Which versions are affected by CVE-2024-50182?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-50182?
Apply the vendor's patch.
Is CVE-2024-50182 being exploited?
There is no known exploitation of CVE-2024-50182 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-53772, BELL-CVE-2024-50182, DEBIAN-CVE-2024-50182, GHSA-9fq4-227m-74p5, UBUNTU-CVE-2024-50182.