Messages in this thread | | | Date | Tue, 9 Nov 2010 17:10:39 -0800 | From | Kees Cook <> | Subject | Re: [Security] [PATCH v3 0/4] x86: clear XD_DISABLED flag on Intel to regain NX |
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Hi Alan,
On Tue, Nov 09, 2010 at 04:43:47PM -0800, Kees Cook wrote: > I looks like there is nothing that actually lists errata directly, so > walking the entire site for lists of all processor types, e.g.: > http://www.intel.com/products/processors/previousgeneration/index.htm > http://www.intel.com/design/celeron/documentation.htm > and then checking spec updates is the only way to go. > > I will report if I find anything bad.
I have reviewed all the spec updates for all the processors I could find (for a total of 45 PDFs). The only mention of XD is for the Dual-Core Xeon 5100[1]:
AG29. #GP Fault is Not Generated on Writing IA32_MISC_ENABLE [34] When Execute Disable (XD) is Not Supported Problem: A #GP fault is not generated on writing to IA32_MISC_ENABLE [34] bit in a processor which does not support Execute Disable (XD) functionality. Implication: Writing to IA32_MISC_ENABLE [34] bit is silently ignored without generating a fault. Workaround: None identified. Status: For the steppings affected, see the Summary Tables of Changes.
But this case is already handled (and doesn't matter) because my patch already avoids this (we only clear IA32_MISC_ENABLE, not set it).
So, based on that, there doesn't seem to be an errata related to _needing_ to disable the XD cpu feature.
-Kees
[1] ftp://download.intel.com/design/Xeon/specupdt/313356.pdf
-- Kees Cook Ubuntu Security Team
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