Skip to content

Draft: CVE-2024-50115: KVM: nSVM: Ignore nCR34:0] when loading PDPTEs from memory

CKI Backport Bot requested to merge redhat/red-hat-ci-tools/kernel/bot-branches/centos-stream-9:backport-RHEL-65871-centos-stream-9-main into main

JIRA: https://issues.redhat.com/browse/RHEL-65871
CVE: CVE-2024-50115

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.

Fixes: e4e517b4be01 ("KVM: MMU: Do not unconditionally read PDPTE from guest memory")
Reported-by: Kirk Swidowski <swidowski@google.com>
Cc: Andy Nguyen <theflow@google.com>
Cc: 3pvd <3pvd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20241009140838.1036226-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit f559b2e9c5c5308850544ab59396b7d53cfc67bd)

Signed-off-by: CKI Backport Bot cki-ci-bot+cki-gitlab-backport-bot@redhat.com

Created 2024-11-05 20:48 UTC by backporter - KWF FAQ - Slack #team-kernel-workflow - Source - Documentation - Report an issue

Merge request reports