28 lines
1.3 KiB
Plaintext
28 lines
1.3 KiB
Plaintext
Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature
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which will be found on future Intel CPUs.
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Memory Protection Keys provides a mechanism for enforcing page-based
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protections, but without requiring modification of the page tables
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when an application changes protection domains. It works by
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dedicating 4 previously ignored bits in each page table entry to a
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"protection key", giving 16 possible keys.
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There is also a new user-accessible register (PKRU) with two separate
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bits (Access Disable and Write Disable) for each key. Being a CPU
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register, PKRU is inherently thread-local, potentially giving each
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thread a different set of protections from every other thread.
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There are two new instructions (RDPKRU/WRPKRU) for reading and writing
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to the new register. The feature is only available in 64-bit mode,
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even though there is theoretically space in the PAE PTEs. These
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permissions are enforced on data access only and have no effect on
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instruction fetches.
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=========================== Config Option ===========================
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This config option adds approximately 1.5kb of text. and 50 bytes of
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data to the executable. A workload which does large O_DIRECT reads
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of holes in XFS files was run to exercise get_user_pages_fast(). No
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performance delta was observed with the config option
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enabled or disabled.
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