UBUNTU-CVE-2024-35804
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
02 / AFFECTED SOFTWARE
Affected packages
50 explicit affected versions
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26 explicit affected versions
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6 explicit affected versions
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37 explicit affected versions
13 explicit affected versions
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26 explicit affected versions
13 explicit affected versions
6 explicit affected versions
29 explicit affected versions
13 explicit affected versions
51 explicit affected versions
49 explicit affected versions
11 explicit affected versions
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23 explicit affected versions
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11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
39 explicit affected versions
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26 explicit affected versions
1 explicit affected versions
13 explicit affected versions
16 explicit affected versions
40 explicit affected versions
3 explicit affected versions
2 explicit affected versions
51 explicit affected versions
2 explicit affected versions
8 explicit affected versions
12 explicit affected versions
37 explicit affected versions
27 explicit affected versions
23 explicit affected versions
12 explicit affected versions
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8 explicit affected versions
10 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
43 explicit affected versions
10 explicit affected versions
12 explicit affected versions
12 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
37 explicit affected versions
37 explicit affected versions
14 explicit affected versions
38 explicit affected versions
40 explicit affected versions
9 explicit affected versions
40 explicit affected versions
11 explicit affected versions
48 explicit affected versions
1 explicit affected versions
8 explicit affected versions
7 explicit affected versions
21 explicit affected versions
4 explicit affected versions
1 explicit affected versions
46 explicit affected versions
13 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
14 explicit affected versions
4 explicit affected versions
11 explicit affected versions
1 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/910c57dfa4d113aae6571c2a8b9ae8c430975902
- https://git.kernel.org/stable/c/225d587a073584946c05c9b7651d637bd45c0c71
- https://git.kernel.org/stable/c/726374dde5d608b15b9756bd52b6fc283fda7a06
- https://git.kernel.org/stable/c/910c57dfa4d113aae6571c2a8b9ae8c430975902
- https://git.kernel.org/stable/c/9d1b22e573a3789ed1f32033ee709106993ba551
- https://git.kernel.org/stable/c/a9bd6bb6f02bf7132c1ab192ba62bbfa52df7d66
- https://ubuntu.com/security/CVE-2024-35804
- https://ubuntu.com/security/notices/USN-6898-1
- https://ubuntu.com/security/notices/USN-6898-2
- https://ubuntu.com/security/notices/USN-6898-3
- https://ubuntu.com/security/notices/USN-6898-4
- https://ubuntu.com/security/notices/USN-6917-1
- https://ubuntu.com/security/notices/USN-6919-1
- https://ubuntu.com/security/notices/USN-6927-1
- https://ubuntu.com/security/notices/USN-7019-1
- https://www.cve.org/CVERecord?id=CVE-2024-35804