CVE-2024-50115 Information

Description

In the Linux kernel the following vulnerability has been resolved:

KVM: nSVM: Ignore nCR3[4:0] when loading PDPTEs from memory

Ignore nCR3[4:0] when loading PDPTEs from memory for nested SVM as bits 4:0 of CR3 are ignored when PAE paging is used and thus VMRUN doesn’t enforce 32-byte alignment of nCR3.

In the absolute worst case scenario failure to ignore bits 4:0 can result in an out-of-bounds read e.g. if the target page is at the end of a memslot and the VMM isn’t using guard pages.

Per the APM:

The CR3 register points to the base address of the page-directory-pointer table. The page-directory-pointer table is aligned on a 32-byte boundary with the low 5 address bits 4:0 assumed to be 0.

And the SDM’s much more explicit:

4:0 Ignored

Note KVM gets this right when loading PDPTRs it’s only the nSVM flow that is broken.

Reference

https://git.kernel.org/stable/c/58cb697d80e669c56197f703e188867c8c54c494 https://git.kernel.org/stable/c/6876793907cbe19d42e9edc8c3315a21e06c32ae https://git.kernel.org/stable/c/2c4adc9b192a0815fe58a62bc0709449416cc884 https://git.kernel.org/stable/c/426682afec71ea3f889b972d038238807b9443e4 https://git.kernel.org/stable/c/f559b2e9c5c5308850544ab59396b7d53cfc67bd