A flaw was found in QEMU's VAPIC (Virtual Advanced Programmable Interrupt Controller) implementation in hw/i386/vapic.c. The 16-bit VAPIC setup hypercall allows a privileged guest to specify both the base address and size of a high-priority writable RAM alias. QEMU does not validate that this alias remains within the VAPIC option ROM boundaries (0xc0000..0xdffff). A malicious guest administrator can place the alias over 0xa0000..0xbffff, bypassing the Q35 chipset's DLCK-protected SMRAM and modifying memory that executes in System Management Mode. This could allow a privileged guest user to inject arbitrary code into locked SMRAM.

Upstream fix: https://gitlab.com/qemu-project/qemu/-/commit/d61c8a6fb7388486353aa267ba0d75b098f16662

Reference: https://gitlab.com/qemu-project/qemu/-/workitems/4206