Bbm #36
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Bbm #36
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ardbiesheuvel
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qwandor
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Oct 20, 2023
walk_range() will be used internally for BBM checks, and this requires that the region passed into the callback represents that actual passed region, without rounding.
jakobvukalovic
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Oct 20, 2023
ardbiesheuvel
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qwandor
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Oct 23, 2023
src/paging.rs
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| /// Block mappings are not permitted, only page mappings | ||
| const NO_BLOCK_MAPPINGS = 1 << 0; | ||
| /// Use of the contiguous bit is not permitted | ||
| const NO_CONTIGUOUS_MAPPINGS = 1 << 1; |
Expose the mapping activate/deactive methods for all target architectures, and just mock it up for non-aarch64 by storing some arbitrary value in previous_ttbr. This will allow us to create test cases for page table updates that are not permitted while the translation is live.
Currently, map_range() accepts the TABLE_OR_PAGE attribute as a flag, and happily sets it on what it assumes to be block mappings, even though setting the bit results in the descriptors in question to be interpreted as table descriptors, turning the output address into a dangling pointer. So reject this attribute.
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src/idmap.rs
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| /// use aarch64_paging::{ | ||
| /// idmap::IdMap, | ||
| /// paging::{Attributes, MemoryRegion}, | ||
| /// paging::{Attributes, Constraints, MemoryRegion}, |
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Looks like Constraints is unused in this example now.
src/lib.rs
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| //! # #[cfg(feature = "alloc")] { | ||
| //! use aarch64_paging::{ | ||
| //! idmap::IdMap, | ||
| //! paging::{Attributes, MemoryRegion}, | ||
| //! paging::{Attributes, Constraints, MemoryRegion}, |
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Ditto, the example doesn't use Constraints.
Add a constraints argument to the map_range() API and use it to implement a NO_BLOCK_MAPPINGS constraint which ensures that all created mappings are mapped down to pages. Also add a NO_CONTIGUOUS_HINT flag for future use - we don't actually ever set that bit so currently there is no need to test for it yet.
The AArch64 architecture is finicky when it comes to changing live page tables, and there are elaborate rules to follow wrt whether an update needs to go via an invalid mapping (break) before creating the new valid mapping (make) Let's add some checks for this: - refuse to split live block entries into table entries - refuse to change the output address - refuse changes to the memory type or clearing the non-global bit
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Implement some checks to ensure that map_range / modify_range do not violate BBM constraints