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vulnerability bulletin CVE-2012-4461

Linux kernel: denial of service via XSAVE

Synthesis of the vulnerability

An attacker, who is located in a qemu+KVM guest system, and on a host system using a processor without xsave/xrstor, can stop the host system.
Impacted products: Debian, BIG-IP Appliance, Fedora, Linux, openSUSE, RHEL, SUSE Linux Enterprise Desktop, SLES.
Severity: 1/4.
Creation date: 07/11/2012.
Identifiers: BID-56414, CERTA-2012-AVI-633, CVE-2012-4461, DSA-2668-1, FEDORA-2012-18684, FEDORA-2012-18691, openSUSE-SU-2013:0925-1, openSUSE-SU-2013:0927-1, RHSA-2013:0223-01, RHSA-2013:0882-01, SOL15797, SUSE-SU-2012:1679-1, SUSE-SU-2013:0786-1, VIGILANCE-VUL-12118.

Description of the vulnerability

The x86 "xsave" and "xrstor" assembler instructions manage the extended state of the processor. These instructions are supported by processors created since 2008.

A user (in a guest system) can use the KVM_SET_SREGS ioctl to set the bit X86_CR4_OSXSAVE in the CR4 register, and can then use the KVM_RUN ioctl. In this case, the kvm_arch_vcpu_ioctl_set_sregs() function uses xsave/xrstor. However, if the processor is anterior to 2008, it does not recognize these instructions, which stops the kernel on the host system.

An attacker, who is located in a qemu+KVM guest system, and on a host system using a processor without xsave/xrstor, can therefore stop the host system.
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