linux-kernel - [PATCH] elf: Fix the arm64 MTE ELF segment name and value

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Date:   Mon, 25 Apr 2022 16:18:33 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Luis Machado <luis.machado@....com>,
        Richard Earnshaw <Richard.Earnshaw@....com>
Subject: [PATCH] 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@....com>
Fixes: 761b9b366cec ("elf: Introduce the ARM MTE ELF segment type")
Cc: Will Deacon <will@...nel.org>
Cc: Jonathan Corbet <corbet@....net>
Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Luis Machado <luis.machado@....com>
Cc: Richard Earnshaw <Richard.Earnshaw@....com>
---

Luckily, the commit being fixed here only went in for 5.18-rc1, so there is no
ABI change in a mainline release.

FYI, the corresponding pull request for the AArch64 ELF ABI:

https://github.com/ARM-software/abi-aa/pull/148

I don't expect any further change to the segment name/value.

 Documentation/arm64/memory-tagging-extension.rst | 4 ++--
 arch/arm64/kernel/elfcore.c                      | 2 +-
 include/uapi/linux/elf.h                         | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documentation/arm64/memory-tagging-extension.rst
index dd27f78d7608..dbae47bba25e 100644
--- a/Documentation/arm64/memory-tagging-extension.rst
+++ b/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
diff --git a/arch/arm64/kernel/elfcore.c b/arch/arm64/kernel/elfcore.c
index 2b3f3d0544b9..98d67444a5b6 100644
--- a/arch/arm64/kernel/elfcore.c
+++ b/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;
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 787c657bfae8..7ce993e6786c 100644
--- a/include/uapi/linux/elf.h
+++ b/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