Linux kernel: missing CPU-state sanitation during task-switch causes DOS / privilege escalation

[halfdog <me () halfdog net>]

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Hello list,

Although of low impact (only some processors/kernels affected,
escalation currently only with mmap_min_addr=0), this might still be
CVE-worthy:

Faults during task-switch due to unhandled FPU-exceptions allow to
kill processes at random on all affected kernels, resulting in local
DOS in the end. One some architectures, privilege escalation under
non-common circumstances is possible, POC for escalation via
shmem_xattr_handlers is available for about 5 days.

See [1] for information about discovery, exploitation, [2] about LKML
discussion, [3] for patch.

hd

[1] http://www.halfdog.net/Security/2013/Vm86SyscallTaskSwitchKernelPanic/
[2] https://lkml.org/lkml/2013/12/28/95
[3]
http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=26bef1318adc1b3a530ecc807ef99346db2aa8b0

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