tree 28280f407c09a9442c825e413d134ce704541989
parent 77704b750553538bc1dc8647f7e53dcafc2e5c4f
author Mitch Phillips <mitchp@google.com> 1669245481 -0800
committer Mitch Phillips <mitchp@google.com> 1700491986 +0100

Linker support for MTE globals.

This patch adds the necessary bionic code for the linker to protect
global data using MTE.

The implementation is described in the MemtagABI addendum to the
AArch64 ELF ABI:
https://github.com/ARM-software/abi-aa/blob/main/memtagabielf64/memtagabielf64.rst

In summary, this patch includes:

1. When MTE globals is requested, the linker maps writable SHF_ALLOC
   sections as anonymous pages with PROT_MTE (copying the file contents
   into the anonymous mapping), rather than using a file-backed private
   mapping. This is required as file-based mappings are not necessarily
   backed by the kernel with tag-capable memory. For sections already
   mapped by the kernel when the linker is invoked via. PT_INTERP, we
   unmap the contents, remap a PROT_MTE+anonymous mapping in its place,
   and re-load the file contents from disk.

2. When MTE globals is requested, the linker tags areas of global memory
   (as defined in SHT_AARCH64_MEMTAG_GLOBALS_DYNAMIC) with random tags,
   but ensuring that adjacent globals are never tagged using the same
   memory tag (to provide detemrinistic overflow detection).

3. Changes to RELATIVE, ABS64, and GLOB_DAT relocations to load and
   store tags in the right places. This ensures that the address tags are
   materialized into the GOT entries as well. These changes are a
   functional no-op to existing binaries and/or non-MTE capable hardware.

Bug: N/A
Test: atest bionic-unit-tests CtsBionicTestCases --test-filter=*Memtag*

Change-Id: Id7b1a925339b14949d5a8f607dd86928624bda0e