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
e8139f585a