elf: Fix the arm64 MTE ELF segment name and value

Unfortunately, the name/value choice for the MTE ELF segment type
(PT_ARM_MEMTAG_MTE) was pretty poor: LOPROC+1 is already in use by
PT_AARCH64_UNWIND, as defined in the AArch64 ELF ABI
(https://github.com/ARM-software/abi-aa/blob/main/aaelf64/aaelf64.rst).

Update the ELF segment type value to LOPROC+2 and also change the define
to PT_AARCH64_MEMTAG_MTE to match the AArch64 ELF ABI namespace. The
AArch64 ELF ABI document is updating accordingly (segment type not
previously mentioned in the document).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 761b9b3 ("elf: Introduce the ARM MTE ELF segment type")
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Machado <luis.machado@arm.com>
Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>
Link: https://lore.kernel.org/r/20220425151833.2603830-1-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: ctmarinas

Documentation/arm64/memory-tagging-extension.rst

@@ -228,10 +228,10 @@ Core dump support
 -----------------
 
 The allocation tags for user memory mapped with ``PROT_MTE`` are dumped
-in the core file as additional ``PT_ARM_MEMTAG_MTE`` segments. The
+in the core file as additional ``PT_AARCH64_MEMTAG_MTE`` segments. The
 program header for such segment is defined as:
 
-:``p_type``: ``PT_ARM_MEMTAG_MTE``
+:``p_type``: ``PT_AARCH64_MEMTAG_MTE``
 :``p_flags``: 0
 :``p_offset``: segment file offset
 :``p_vaddr``: segment virtual address, same as the corresponding

arch/arm64/kernel/elfcore.c

@@ -95,7 +95,7 @@ int elf_core_write_extra_phdrs(struct coredump_params *cprm, loff_t offset)
 	for_each_mte_vma(current, vma) {
 		struct elf_phdr phdr;
 
-		phdr.p_type = PT_ARM_MEMTAG_MTE;
+		phdr.p_type = PT_AARCH64_MEMTAG_MTE;
 		phdr.p_offset = offset;
 		phdr.p_vaddr = vma->vm_start;
 		phdr.p_paddr = 0;

include/uapi/linux/elf.h

@@ -42,7 +42,7 @@ typedef __s64	Elf64_Sxword;
 
 
 /* ARM MTE memory tag segment type */
-#define PT_ARM_MEMTAG_MTE	(PT_LOPROC + 0x1)
+#define PT_AARCH64_MEMTAG_MTE	(PT_LOPROC + 0x2)
 
 /*
  * Extended Numbering