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ae84739c27
Intel CPUs have an additional MSR bit to indicate if the BIOS was configured to disable the NX cpu feature. This bit was traditionally used for operating systems that did not understand how to handle the NX bit. Since Linux understands this, this BIOS flag should be ignored by default. In a review[1] of reported hardware being used by Ubuntu bug reporters, almost 10% of systems had an incorrectly configured BIOS, leaving their systems unable to use the NX features of their CPU. This change will clear the MSR_IA32_MISC_ENABLE_XD_DISABLE bit so that NX cannot be inappropriately controlled by the BIOS on Intel CPUs. If, under very strange hardware configurations, NX actually needs to be disabled, "noexec=off" can be used to restore the prior behavior. [1] http://www.outflux.net/blog/archives/2010/02/18/data-mining-for-nx-bit/ Signed-off-by: Kees Cook <kees.cook@canonical.com> LKML-Reference: <1289414154-7829-3-git-send-email-kees.cook@canonical.com> Acked-by: Pekka Enberg <penberg@kernel.org> Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> |
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