CVE-2026-80853

In the Linux kernel, the following vulnerability has been resolved:

KVM: SEV: Allocate full pages for {DE,EN}CRYPT ops on SNP-enabled hosts

When {de,en}crypting memory of an SEV or SEV-ES guest on an SNP-enabled host via a temporary buffer, allocate a full 4KiB page for the buffer to ensure the page containing the buffer is wholly owned by KVM, i.e. won't be concurrently allocated and accessed by other kernel code while KVM is using the buffer to {de,en}crypt memory. On SNP-enabled platforms, when sending SEV/SEV-ES commands that trigger firmware writes to memory, the to-be-written page(s) must be (temporarily) assigned to Firmware (as required by the SNP architecture, to guard against using such commands as gadgets to attack SNP guests). See snp map cmd buf desc() and friends.

Unfortunately, transferring ownership of a page to Firmware makes the page inaccessible to software, and thus writes generate RMP #PF violations. If KVM uses a sub-page allocation for its temporary buffer, some other actor in the kernel can allocate and use the other portions of the page, and thus trigger unexpected (and seemingly spurious) RMP #PF violations due to software attempting to access a Firmware-owned page.

BUG: unable to handle page fault for address: ffff906ae30f0300 #PF: supervisor write access in kernel mode #PF: error code(0x80000003) - RMP violation PGD 6b1b80d067 P4D 6b1b80d067 PUD 100231e2063 PMD 10055a88063 PTE 80000100630f0163 SEV-SNP: PFN 0x100630f0 unassigned, dumping non-zero entries in 2M PFN region: [0x10063000 - 0x10063200] Oops: Oops: 0003 [#1] SMP CPU: 70 UID: 0 PID: 10658 Comm: svw WaiterThrea Tainted: G U W O 7.1.0-smp--c22293789940-seanjc-next #1 PREEMPTLAZY Tainted: [U]=USER, [W]=WARN, [O]=OOT MODULE Hardware name: Google, Inc. Arcadia IT 80/Arcadia IT 80, BIOS 34.86.0-102 01/25/2026 RIP: 0010:memset+0xf/0x20 Call Trace: kvmalloc node noprof+0x2a4/0x710 do getxattr+0x4e/0x130 path getxattrat+0x125/0x1b0 do syscall 64+0x10a/0x480 entry SYSCALL 64 after hwframe+0x4b/0x53 RIP: 0033:0x7f3a22cb6daa Modules linked in: kvm amd kvm irqbypass vfat fat ccp k10temp sha3 libsha3 i2c piix4 gq(O) cdc acm xhci pci xhci hcd gsmi: Log Shutdown Reason 0x03 CR2: ffff906ae30f0300 ---[ end trace 0000000000000000 ]--- RIP: 0010:memset+0xf/0x20 Kernel panic - not syncing: Fatal exception Kernel Offset: 0x39e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) gsmi: Log Shutdown Reason 0x02