Documentation: x86: convert pti.txt to reST
This converts the plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du <changbin.du@gmail.com> Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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@ -21,3 +21,4 @@ x86-specific Documentation
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protection-keys
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intel_mpx
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amd-memory-encryption
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pti
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@ -1,9 +1,15 @@
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.. SPDX-License-Identifier: GPL-2.0
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==========================
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Page Table Isolation (PTI)
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==========================
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Overview
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========
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Page Table Isolation (pti, previously known as KAISER[1]) is a
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Page Table Isolation (pti, previously known as KAISER [1]_) is a
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countermeasure against attacks on the shared user/kernel address
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space such as the "Meltdown" approach[2].
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space such as the "Meltdown" approach [2]_.
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To mitigate this class of attacks, we create an independent set of
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page tables for use only when running userspace applications. When
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@ -60,6 +66,7 @@ Protection against side-channel attacks is important. But,
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this protection comes at a cost:
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1. Increased Memory Use
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a. Each process now needs an order-1 PGD instead of order-0.
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(Consumes an additional 4k per process).
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b. The 'cpu_entry_area' structure must be 2MB in size and 2MB
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@ -68,6 +75,7 @@ this protection comes at a cost:
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is decompressed, but no space in the kernel image itself.
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2. Runtime Cost
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a. CR3 manipulation to switch between the page table copies
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must be done at interrupt, syscall, and exception entry
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and exit (it can be skipped when the kernel is interrupted,
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@ -142,6 +150,7 @@ ideally doing all of these in parallel:
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interrupted, including nested NMIs. Using "-c" boosts the rate of
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NMIs, and using two -c with separate counters encourages nested NMIs
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and less deterministic behavior.
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::
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while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done
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@ -182,5 +191,5 @@ that are worth noting here.
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tended to be TLB invalidation issues. Usually invalidating
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the wrong PCID, or otherwise missing an invalidation.
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1. https://gruss.cc/files/kaiser.pdf
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2. https://meltdownattack.com/meltdown.pdf
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.. [1] https://gruss.cc/files/kaiser.pdf
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.. [2] https://meltdownattack.com/meltdown.pdf
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