kernel: execution possible in non-executable mappings in recent 2.6 kernels (SPARC only)

[Eugene Teo <eugeneteo () kernel sg>]

http://marc.info/?l=linux-sparc&m=126662196902830&w=2
http://marc.info/?l=linux-sparc&m=126662159602378&w=2

sparc64: Fix sun4u execute bit check in TSB I-TLB load.

TSB I-tlb load code tries to use andcc to check the _PAGE_EXEC_4U bit,
but that's bit 12 so it gets sign extended all the way up to bit 63
and the test nearly always passes as a result.

Use sethi to fix the bug.

I'm not requesting a CVE for this as this does not affect any of our 
kernels. But just a heads-up for those not aware of this.

Thanks, Eugene