UBUNTU-CVE-2024-50102
In the Linux kernel, the following vulnerability has been resolved: x86: fix user address masking non-canonical speculation issue It turns out that AMD has a "Meltdown Lite(tm)" issue with non-canonical accesses in kernel space. And so using just the high bit to decide whether an access is in user space or kernel space ends up with the good old "leak speculative data" if you have the right gadget using the result: CVE-2020-12965 “Transient Execution of Non-Canonical Accesses“ Now, the kernel surrounds the access with a STAC/CLAC pair, and those instructions end up serializing execution on older Zen architectures, which closes the speculation window. But that was true only up until Zen 5, which renames the AC bit [1]. That improves performance of STAC/CLAC a lot, but also means that the speculation window is now open. Note that this affects not just the new address masking, but also the regular valid_user_address() check used by access_ok(), and the asm version of the sign bit check in the get_user() helpers. It does not affect put_user() or clear_user() variants, since there's no speculative result to be used in a gadget for those operations.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
50 explicit affected versions
6 explicit affected versions
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19 explicit affected versions
6 explicit affected versions
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26 explicit affected versions
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42 explicit affected versions
13 explicit affected versions
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35 explicit affected versions
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48 explicit affected versions
13 explicit affected versions
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55 explicit affected versions
1 explicit affected versions
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10 explicit affected versions
51 explicit affected versions
7 explicit affected versions
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1 explicit affected versions
12 explicit affected versions
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1 explicit affected versions
7 explicit affected versions
19 explicit affected versions
12 explicit affected versions
12 explicit affected versions
44 explicit affected versions
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37 explicit affected versions
37 explicit affected versions
10 explicit affected versions
13 explicit affected versions
42 explicit affected versions
10 explicit affected versions
26 explicit affected versions
12 explicit affected versions
13 explicit affected versions
29 explicit affected versions
13 explicit affected versions
43 explicit affected versions
43 explicit affected versions
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23 explicit affected versions
10 explicit affected versions
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11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
10 explicit affected versions
26 explicit affected versions
42 explicit affected versions
37 explicit affected versions
48 explicit affected versions
13 explicit affected versions
48 explicit affected versions
16 explicit affected versions
53 explicit affected versions
3 explicit affected versions
1 explicit affected versions
51 explicit affected versions
7 explicit affected versions
43 explicit affected versions
12 explicit affected versions
27 explicit affected versions
45 explicit affected versions
8 explicit affected versions
5 explicit affected versions
3 explicit affected versions
8 explicit affected versions
10 explicit affected versions
49 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
2 explicit affected versions
10 explicit affected versions
12 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
37 explicit affected versions
53 explicit affected versions
14 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
42 explicit affected versions
21 explicit affected versions
8 explicit affected versions
7 explicit affected versions
4 explicit affected versions
1 explicit affected versions
13 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
48 explicit affected versions
14 explicit affected versions
4 explicit affected versions
11 explicit affected versions
1 explicit affected versions
22 explicit affected versions
41 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: x86: fix user address masking non-canonical speculation issue It turns out that AMD has a "Meltdown Lite(tm)" issue with non-canonical accesses in kernel space. And so using just the high bit to decide whether an access is in user space or kernel space ends up with the good old "leak speculative data" if you have the right gadget using the result: CVE-2020-12965 “Transient Execution of Non-Canonical Accesses“ Now, the kernel surrounds the access with a STAC/CLAC pair, and those instructions end up serializing execution on older Zen architectures, which closes the speculation window. But that was true only up until Zen 5, which renames the AC bit [1]. That improves performance of STAC/CLAC a lot, but also means that the speculation window is now open. Note that this affects not just the new address masking, but also the regular valid_user_address() check used by access_ok(), and the asm version of the sign bit check in the get_user() helpers. It does not affect put_user() or clear_user() variants, since there's no speculative result to be used in a gadget for those operations.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/86e6b1547b3d013bc392adf775b89318441403c2
- https://git.kernel.org/stable/c/291313693677a345d4f50aae3c68e28b469f601e
- https://git.kernel.org/stable/c/86e6b1547b3d013bc392adf775b89318441403c2
- https://ubuntu.com/security/CVE-2024-50102
- https://ubuntu.com/security/notices/USN-7276-1
- https://ubuntu.com/security/notices/USN-7277-1
- https://ubuntu.com/security/notices/USN-7310-1
- https://www.cve.org/CVERecord?id=CVE-2024-50102