[PATCH 4/5] arm64: mte: Dump the MTE tags in the core file

[Luis Machado]

On 12/8/21 9:19 AM, Catalin Marinas wrote:
> For each vma mapped with PROT_MTE (the VM_MTE flag set), generate a
> PT_ARM_MEMTAG_MTE segment in the core file and dump the corresponding
> tags. The in-file size for such segments is 128 bytes per page.
> 
> For pages in a VM_MTE vma which are not present in the user page tables
> or don't have the PG_mte_tagged flag set (e.g. execute-only), just write
> zeros in the core file.
> 
> An example of program headers for two vmas, one 2-page, the other 4-page
> long:
> 
>    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
>    ...
>    LOAD           0x030000 0x0000ffff80034000 0x0000000000000000 0x000000 0x002000 RW  0x1000
>    LOAD           0x030000 0x0000ffff80036000 0x0000000000000000 0x004000 0x004000 RW  0x1000
>    ...
>    LOPROC+0x1     0x05b000 0x0000ffff80034000 0x0000000000000000 0x000100 0x002000     0
>    LOPROC+0x1     0x05b100 0x0000ffff80036000 0x0000000000000000 0x000200 0x004000     0
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> ---
>   arch/arm64/Kconfig          |   1 +
>   arch/arm64/kernel/Makefile  |   1 +
>   arch/arm64/kernel/elfcore.c | 123 ++++++++++++++++++++++++++++++++++++
>   3 files changed, 125 insertions(+)
>   create mode 100644 arch/arm64/kernel/elfcore.c
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c4207cf9bb17..fe5d72dd5a3b 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -10,6 +10,7 @@ config ARM64
>   	select ACPI_SPCR_TABLE if ACPI
>   	select ACPI_PPTT if ACPI
>   	select ARCH_HAS_DEBUG_WX
> +	select ARCH_BINFMT_ELF_EXTRA_PHDRS
>   	select ARCH_BINFMT_ELF_STATE
>   	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
>   	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 88b3e2a21408..986837d7ec82 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -61,6 +61,7 @@ obj-$(CONFIG_ARM64_ACPI_PARKING_PROTOCOL)	+= acpi_parking_protocol.o
>   obj-$(CONFIG_PARAVIRT)			+= paravirt.o
>   obj-$(CONFIG_RANDOMIZE_BASE)		+= kaslr.o
>   obj-$(CONFIG_HIBERNATION)		+= hibernate.o hibernate-asm.o
> +obj-$(CONFIG_ELF_CORE)			+= elfcore.o
>   obj-$(CONFIG_KEXEC_CORE)		+= machine_kexec.o relocate_kernel.o	\
>   					   cpu-reset.o
>   obj-$(CONFIG_KEXEC_FILE)		+= machine_kexec_file.o kexec_image.o
> diff --git a/arch/arm64/kernel/elfcore.c b/arch/arm64/kernel/elfcore.c
> new file mode 100644
> index 000000000000..3455ee4acc04
> --- /dev/null
> +++ b/arch/arm64/kernel/elfcore.c
> @@ -0,0 +1,123 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/coredump.h>
> +#include <linux/elfcore.h>
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +
> +#include <asm/cpufeature.h>
> +#include <asm/mte.h>
> +
> +#define for_each_mte_vma(tsk, vma)					\
> +	if (system_supports_mte())					\
> +		for (vma = tsk->mm->mmap; vma; vma = vma->vm_next)	\
> +			if (vma->vm_flags & VM_MTE)
> +
> +static unsigned long mte_vma_tag_dump_size(struct vm_area_struct *vma)
> +{
> +	if (vma->vm_flags & VM_DONTDUMP)
> +		return 0;
> +
> +	return vma_pages(vma) * MTE_PAGE_TAG_STORAGE;
> +}
> +
> +/* Derived from dump_user_range(); start/end must be page-aligned */
> +static int mte_dump_tag_range(struct coredump_params *cprm,
> +			      unsigned long start, unsigned long end)
> +{
> +	unsigned long addr;
> +
> +	for (addr = start; addr < end; addr += PAGE_SIZE) {
> +		char tags[MTE_PAGE_TAG_STORAGE];
> +		struct page *page = get_dump_page(addr);
> +
> +		/*
> +		 * get_dump_page() returns NULL when encountering an empty
> +		 * page table entry that would otherwise have been filled with
> +		 * the zero page. Skip the equivalent tag dump which would
> +		 * have been all zeros.
> +		 */
> +		if (!page) {
> +			dump_skip(cprm, MTE_PAGE_TAG_STORAGE);
> +			continue;
> +		}
> +
> +		/*
> +		 * Pages mapped in user space as !pte_access_permitted() (e.g.
> +		 * PROT_EXEC only) may not have the PG_mte_tagged flag set.
> +		 */
> +		if (!test_bit(PG_mte_tagged, &page->flags)) {
> +			put_page(page);
> +			dump_skip(cprm, MTE_PAGE_TAG_STORAGE);
> +			continue;
> +		}
> +
> +		mte_save_page_tags(page_address(page), tags);
> +		put_page(page);
> +		if (!dump_emit(cprm, tags, MTE_PAGE_TAG_STORAGE))
> +			return 0;
> +	}
> +
> +	return 1;
> +}
> +
> +Elf_Half elf_core_extra_phdrs(void)
> +{
> +	struct vm_area_struct *vma;
> +	int vma_count = 0;
> +
> +	for_each_mte_vma(current, vma)
> +		vma_count++;
> +
> +	return vma_count;
> +}
> +
> +int elf_core_write_extra_phdrs(struct coredump_params *cprm, loff_t offset)
> +{
> +	struct vm_area_struct *vma;
> +
> +	for_each_mte_vma(current, vma) {
> +		struct elf_phdr phdr;
> +
> +		phdr.p_type = PT_ARM_MEMTAG_MTE;
> +		phdr.p_offset = offset;
> +		phdr.p_vaddr = vma->vm_start;
> +		phdr.p_paddr = 0;
> +		phdr.p_filesz = mte_vma_tag_dump_size(vma);
> +		phdr.p_memsz = vma->vm_end - vma->vm_start;
> +		offset += phdr.p_filesz;
> +		phdr.p_flags = 0;
> +		phdr.p_align = 0;
> +
> +		if (!dump_emit(cprm, &phdr, sizeof(phdr)))
> +			return 0;
> +	}
> +
> +	return 1;
> +}
> +
> +size_t elf_core_extra_data_size(void)
> +{
> +	struct vm_area_struct *vma;
> +	size_t data_size = 0;
> +
> +	for_each_mte_vma(current, vma)
> +		data_size += mte_vma_tag_dump_size(vma);
> +
> +	return data_size;
> +}
> +
> +int elf_core_write_extra_data(struct coredump_params *cprm)
> +{
> +	struct vm_area_struct *vma;
> +
> +	for_each_mte_vma(current, vma) {
> +		if (vma->vm_flags & VM_DONTDUMP)
> +			continue;
> +
> +		if (!mte_dump_tag_range(cprm, vma->vm_start, vma->vm_end))
> +			return 0;
> +	}
> +
> +	return 1;
> +}
> 

Acked-by: Luis Machado <luis.machado at linaro.org>