On Wed, Aug 06, 2025 at 10:18:14PM +0600, Svetlana Parfenova wrote:
> Preserve the original ELF e_flags from the executable in the core dump
> header instead of relying on compile-time defaults (ELF_CORE_EFLAGS or
> value from the regset view). This ensures that ABI-specific flags in
> the dump file match the actual binary being executed.
>
> Save the e_flags field during ELF binary loading (in load_elf_binary())
> into the mm_struct, and later retrieve it during core dump generation
> (in fill_note_info()). Use this saved value to populate the e_flags in
> the core dump ELF header.
>
> Add a new Kconfig option, CONFIG_CORE_DUMP_USE_PROCESS_EFLAGS, to guard
> this behavior. Although motivated by a RISC-V use case, the mechanism is
> generic and can be applied to all architectures.
In the general case, is e_flags mismatched? i.e. why hide this behind a
Kconfig? Put another way, if I enabled this Kconfig and dumped core from
some regular x86_64 process, will e_flags be different?
> This change is needed to resolve a debugging issue encountered when
> analyzing core dumps with GDB for RISC-V systems. GDB inspects the
> e_flags field to determine whether optional register sets such as the
> floating-point unit are supported. Without correct flags, GDB may warn
> and ignore valid register data:
>
> warning: Unexpected size of section '.reg2/213' in core file.
>
> As a result, floating-point registers are not accessible in the debugger,
> even though they were dumped. Preserving the original e_flags enables
> GDB and other tools to properly interpret the dump contents.
>
> Signed-off-by: Svetlana Parfenova <svetlana.parfenova@xxxxxxxxxxxxx>
> ---
> fs/Kconfig.binfmt | 9 +++++++++
> fs/binfmt_elf.c | 26 ++++++++++++++++++++------
> include/linux/mm_types.h | 5 +++++
> 3 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index bd2f530e5740..45bed2041542 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -184,4 +184,13 @@ config EXEC_KUNIT_TEST
> This builds the exec KUnit tests, which tests boundary conditions
> of various aspects of the exec internals.
>
> +config CORE_DUMP_USE_PROCESS_EFLAGS
> + bool "Preserve ELF e_flags from executable in core dumps"
> + depends on BINFMT_ELF && ELF_CORE && RISCV
> + default n
> + help
> + Save the ELF e_flags from the process executable at load time
> + and use it in the core dump header. This ensures the dump reflects
> + the original binary ABI.
> +
> endmenu
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index caeddccaa1fe..e5e06e11f9fc 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1290,6 +1290,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> mm->end_data = end_data;
> mm->start_stack = bprm->p;
>
> +#ifdef CONFIG_CORE_DUMP_USE_PROCESS_EFLAGS
> + /* stash e_flags for use in core dumps */
> + mm->saved_e_flags = elf_ex->e_flags;
> +#endif
Is this structure actually lost during ELF load? I thought we preserved
some more of the ELF headers during load...
> +
> /**
> * DOC: "brk" handling
> *
> @@ -1804,6 +1809,8 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
> struct elf_thread_core_info *t;
> struct elf_prpsinfo *psinfo;
> struct core_thread *ct;
> + u16 machine;
> + u32 flags;
>
> psinfo = kmalloc(sizeof(*psinfo), GFP_KERNEL);
> if (!psinfo)
> @@ -1831,17 +1838,24 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
> return 0;
> }
>
> - /*
> - * Initialize the ELF file header.
> - */
> - fill_elf_header(elf, phdrs,
> - view->e_machine, view->e_flags);
> + machine = view->e_machine;
> + flags = view->e_flags;
> #else
> view = NULL;
> info->thread_notes = 2;
> - fill_elf_header(elf, phdrs, ELF_ARCH, ELF_CORE_EFLAGS);
> + machine = ELF_ARCH;
> + flags = ELF_CORE_EFLAGS;
> #endif
>
> +#ifdef CONFIG_CORE_DUMP_USE_PROCESS_EFLAGS
> + flags = dump_task->mm->saved_e_flags;
> +#endif
This appears to clobber the value from view->e_flags. Is that right? It
feels like this change should only be needed in the default
ELF_CORE_EFLAGS case. How is view->e_flags normally set?
> +
> + /*
> + * Initialize the ELF file header.
> + */
> + fill_elf_header(elf, phdrs, machine, flags);
> +
> /*
> * Allocate a structure for each thread.
> */
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index d6b91e8a66d6..39921b32e4f5 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1098,6 +1098,11 @@ struct mm_struct {
>
> unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
>
> +#ifdef CONFIG_CORE_DUMP_USE_PROCESS_EFLAGS
> + /* the ABI-related flags from the ELF header. Used for core dump */
> + unsigned long saved_e_flags;
> +#endif
> +
> struct percpu_counter rss_stat[NR_MM_COUNTERS];
>
> struct linux_binfmt *binfmt;
> --
> 2.50.1
>
-Kees
--
Kees Cook
