CVE-2024-35875 Affecting kernel-rt-debug package, versions <0:5.14.0-427.35.1.el9_4
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published4 Nov 2024
- disclosed11 Sept 2024
Introduced: 11 Sep 2024
CVE-2024-35875 (opens in a new tab)How to fix?
Upgrade AlmaLinux:9 kernel-rt-debug to version 0:5.14.0-427.35.1.el9_4 or higher.
This issue was patched in ALSA-2024:6567.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-rt-debug package and not the kernel-rt-debug package as distributed by AlmaLinux.
See How to fix? for AlmaLinux:9 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
x86/coco: Require seeding RNG with RDRAND on CoCo systems
There are few uses of CoCo that don't rely on working cryptography and hence a working RNG. Unfortunately, the CoCo threat model means that the VM host cannot be trusted and may actively work against guests to extract secrets or manipulate computation. Since a malicious host can modify or observe nearly all inputs to guests, the only remaining source of entropy for CoCo guests is RDRAND.
If RDRAND is broken -- due to CPU hardware fault -- the RNG as a whole is meant to gracefully continue on gathering entropy from other sources, but since there aren't other sources on CoCo, this is catastrophic. This is mostly a concern at boot time when initially seeding the RNG, as after that the consequences of a broken RDRAND are much more theoretical.
So, try at boot to seed the RNG using 256 bits of RDRAND output. If this fails, panic(). This will also trigger if the system is booted without RDRAND, as RDRAND is essential for a safe CoCo boot.
Add this deliberately to be "just a CoCo x86 driver feature" and not part of the RNG itself. Many device drivers and platforms have some desire to contribute something to the RNG, and add_device_randomness() is specifically meant for this purpose.
Any driver can call it with seed data of any quality, or even garbage quality, and it can only possibly make the quality of the RNG better or have no effect, but can never make it worse.
Rather than trying to build something into the core of the RNG, consider the particular CoCo issue just a CoCo issue, and therefore separate it all out into driver (well, arch/platform) code.
[ bp: Massage commit message. ]
References
- https://errata.almalinux.org/9/ALSA-2024-6567.html
- https://access.redhat.com/security/cve/CVE-2024-35875
- https://access.redhat.com/errata/RHSA-2024:6567
- https://git.kernel.org/stable/c/08044b08b37528b82f70a87576c692b4e4b7716e
- https://git.kernel.org/stable/c/22943e4fe4b3a2dcbadc3d38d5bf840bbdbfe374
- https://git.kernel.org/stable/c/453b5f2dec276c1bb4ea078bf8c0da57ee4627e5
- https://git.kernel.org/stable/c/99485c4c026f024e7cb82da84c7951dbe3deb584