| Description: | kernel KVM before versions kernel 4.16, kernel 4.16-rc7, kernel 4.17-rc1, kernel 4.17-rc2 and kernel 4.17-rc3 is vulnerable to a flaw in the way the Linux kernel's KVM hypervisor handled exceptions delivered after a stack switch operation via Mov SS or Pop SS instructions. During the stack switch operation, the processor did not deliver interrupts and exceptions, rather they are delivered once the first instruction after the stack switch is executed. An unprivileged KVM guest user could use this flaw to crash the guest or, potentially, escalate their privileges in the guest. Andy Lutomirski discovered that the KVM subsystem of the Linux kernel did not properly emulate the ICEBP instruction following a MOV/POP to SS instruction. A local attacker in a KVM virtual machine could use this to cause a denial of service (guest VM crash) or possibly escalate privileges inside of the virtual machine. This issue only affected the i386 and amd64 architectures.
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