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Diffstat (limited to 'Documentation/arch/x86/pti.rst')
| -rw-r--r-- | Documentation/arch/x86/pti.rst | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/Documentation/arch/x86/pti.rst b/Documentation/arch/x86/pti.rst index 4b858a9bad8d..e08d35177bc0 100644 --- a/Documentation/arch/x86/pti.rst +++ b/Documentation/arch/x86/pti.rst @@ -81,11 +81,9 @@ this protection comes at a cost: and exit (it can be skipped when the kernel is interrupted, though.) Moves to CR3 are on the order of a hundred cycles, and are required at every entry and exit. - b. A "trampoline" must be used for SYSCALL entry. This - trampoline depends on a smaller set of resources than the - non-PTI SYSCALL entry code, so requires mapping fewer - things into the userspace page tables. The downside is - that stacks must be switched at entry time. + b. Percpu TSS is mapped into the user page tables to allow SYSCALL64 path + to work under PTI. This doesn't have a direct runtime cost but it can + be argued it opens certain timing attack scenarios. c. Global pages are disabled for all kernel structures not mapped into both kernel and userspace page tables. This feature of the MMU allows different processes to share TLB @@ -167,7 +165,7 @@ that are worth noting here. * Failures of the selftests/x86 code. Usually a bug in one of the more obscure corners of entry_64.S * Crashes in early boot, especially around CPU bringup. Bugs - in the trampoline code or mappings cause these. + in the mappings cause these. * Crashes at the first interrupt. Caused by bugs in entry_64.S, like screwing up a page table switch. Also caused by incorrectly mapping the IRQ handler entry code. |