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Move debug related pages from Guides to a separate top level page. This way all pages related to debugging will be in one place which is more user friendly. Related Github issue: https://github.com/apache/nuttx/issues/15667 Signed-off-by: raiden00pl <raiden00@railab.me>
96 lines
3.9 KiB
ReStructuredText
96 lines
3.9 KiB
ReStructuredText
====================================
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ATM64 MTE extension
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====================================
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Introduction
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------------
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Arm v8.5 introduced the Arm Memory Tagging Extension (MTE),
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a hardware implementation of tagged memory.
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Basically, MTE tags every memory allocation/deallocation
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with additional metadata. It assigns a tag to a memory location,
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which can then be associated with a pointer that references
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that memory location. At runtime, the CPU checks that the pointer
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and metadata tags match with every load and store.
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NX OS currently supports deploying MTE on ARM64 QEMU,
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which is supported at the EL1 level of NX OS.
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Principle
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---------
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The Arm Memory Tagging Extension implements lock and key access to memory.
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Locks can be set on memory and keys provided during memory access. If the key matches
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the lock, the access is permitted. If it does not match, an error is reported.
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Memory locations are tagged by adding four bits of metadata to each 16 bytes
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of physical memory. This is the Tag Granule. Tagging memory implements the lock.
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Pointers, and therefore virtual addresses, are modified to contain the key.
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In order to implement the key bits without requiring larger pointers MTE uses the Top Byte
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Ignore (TBI) feature of the Armv8-A Architecture. When TBI is enabled, the top byte of
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a virtual address is ignored when using it as an input for address translation. This allows the
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top byte to store metadata. In MTE four bits of the top byte are used to provide the key
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Architectural Details
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---------------------
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MTE adds instructions to the Armv8-A Architecture that are outlined below and grouped
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into three different categories [6]:
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Instructions for tag manipulation applicable to stack and heap tagging.
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IRG
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In order for the statistical basis of MTE to be valid, a source of random tags is required.
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IRG is defined to provide this in hardware and insert such a tag into a register for use
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by other instructions.
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GMI
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This instruction is for manipulating the excluded set of tags for use with the IRG instruction.
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This is intended for cases where software uses specific tag values for special purposes
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while retaining random tag behavior for normal allocations.
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LDG, STG, and STZG
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These instructions allow getting or setting tags in memory. They are intended for changing
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tags in memory either without modifying the data or zeroing the data.
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ST2G and STZ2G
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These are denser alternatives to STG and STZG which operate on two granules of memory
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when allocation size allows them to be used.
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STGP
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This instruction stores both tag and data to memory.
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Instructions Intended for pointer arithmetic and stack tagging:
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ADDG and SUBG
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These are variants of the ADD and SUB instructions, intended for arithmetic on addresses.
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They allow both the tag and address to be separately modified by an immediate value.
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These instructions are intended for creating the addresses of objects on the stack.
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SUBP(S)
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This instruction provides a 56-bit subtract with optional flag setting which is required
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for pointer arithmetic that ignores the tag in the top byte.
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Instructions intended for system use:
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LDGM, STGM, and STZGM
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These are bulk tag manipulation instructions which are UNDEFINED at EL0. These are
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intended for system software to manipulate tags for the purposes of initialization and
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serialization. For example, they can be used to implement swapping of tagged memory
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to a medium which is not tag-aware. The zeroing form can be used for efficient
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initialization of memory.
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Currently NX OS supports the execution of the above instructions,
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such as irg, ldg, stg instructions.
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Their test programs are stored in "apps/system/mte" to test whether the current system supports
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Usage
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-----
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If you want to experience the MTE function of NX OS, you can refer to the following：
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To enable ARM64_MTE, configure the kernel with::
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CONFIG_ARM64_MTE=y
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Of course you can also run it with the existing configuration：
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boards/arm64/qemu/qemu-armv8a/configs/mte
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