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

Vulnerability 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.

References

• https://git.kernel.org/stable/c/76ce386feb14ec9a460784fcd495d8432acce7a5
• 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