CVE-2024-35804 KVM: x86: Mark target gfn of emulated atomic instruction as dirty
KVM fails to mark guest memory as dirty during emulated atomic instructions, causing data corruption during live migration.
- 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-2024-35804?
CVE-2024-35804 is a high-severity vulnerability in Linux kernel, published on 17 May 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:
KVM: x86: Mark target gfn of emulated atomic instruction as dirty
When emulating an atomic access on behalf of the guest, mark the target gfn dirty if the CMPXCHG by KVM is attempted and doesn't fault. This fixes a bug where KVM effectively corrupts guest memory during live migration by writing to guest memory without informing userspace that the page is dirty.
Marking the page dirty got unintentionally dropped when KVM's emulated CMPXCHG was converted to do a user access. Before that, KVM explicitly mapped the guest page into kernel memory, and marked the page dirty during the unmap phase.
Mark the page dirty even if the CMPXCHG fails, as the old data is written back on failure, i.e. the page is still written. The value written is guaranteed to be the same because the operation is atomic, but KVM's ABI is that all writes are dirty logged regardless of the value written. And more importantly, that's what KVM did before the buggy commit.
Huge kudos to the folks on the Cc list (and many others), who did all the actual work of triaging and debugging.
base-commit: 6769ea8da8a93ed4630f1ce64df6aafcaabfce64
Weakness: CWE-401
Which versions are affected by CVE-2024-35804?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-35804?
Apply the vendor's patch.
Is CVE-2024-35804 being exploited?
There is no known exploitation of CVE-2024-35804 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-35804, DEBIAN-CVE-2024-35804, GHSA-x3cp-9cgr-m6gc, UBUNTU-CVE-2024-35804.