Messages in this thread | | | Subject | Re: [RFC][PATCH 03/10] x86/mm: introduce "default" kernel PTE mask | From | Tom Lendacky <> | Date | Thu, 22 Feb 2018 17:11:36 -0600 |
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On 2/22/2018 4:26 PM, Dave Hansen wrote: > On 02/22/2018 02:21 PM, Nadav Amit wrote: >> Dave Hansen <dave.hansen@linux.intel.com> wrote: >>> From: Dave Hansen <dave.hansen@linux.intel.com> >>> The __PAGE_KERNEL_* page permissions are "raw". They contain bits >>> that may or may not be supported on the current processor. They >>> need to be filtered by a mask (currently __supported_pte_mask) to >>> turn them into a value that we can actually set in a PTE. >>> >>> These __PAGE_KERNEL_* values all contain _PAGE_GLOBAL. But, with >>> PTI, we want to be able to support _PAGE_GLOBAL (have the bit set >>> in __supported_pte_mask) but not have it appear in any of these >>> masks by default. >> >> There might be a potential issue with this approach. __supported_pte_mask is >> exported, so out-of-tree modules might use it. They therefore can >> unknowingly use this value to set PTEs with _PAGE_GLOBAL set. > > I don't think we can help out-of-tree modules getting this wrong. > They're OK if they use PAGE_KERNEL*, btw.
You will probably need to change __default_kernel_pte_mask to be an EXPORT_SYMBOL instead of an EXPORT_SYMBOL_GPL for (some) out-of-tree modules.
Thanks, Tom
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