On Mon, Aug 11, 2025 at 03:53:28PM +0600, Svetlana Parfenova wrote:
> Some architectures, such as RISC-V, use the ELF e_flags field to encode
> ABI-specific information (e.g., ISA extensions, fpu support). Debuggers
> like GDB rely on these flags in core dumps to correctly interpret
> optional register sets. If the flags are missing or incorrect, GDB may
> warn and ignore valid data, for example:
>
> warning: Unexpected size of section '.reg2/213' in core file.
>
> This can prevent access to fpu or other architecture-specific registers
> even when they were dumped.
>
> 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()). A new macro ELF_CORE_USE_PROCESS_EFLAGS allows
> architectures to enable this behavior - currently just RISC-V.
>
> Signed-off-by: Svetlana Parfenova <svetlana.parfenova@xxxxxxxxxxxxx>
> ---
> Changes in v2:
> - Remove usage of Kconfig option.
> - Add an architecture-optional macro to set process e_flags. Enabled
> by defining ELF_CORE_USE_PROCESS_EFLAGS. Defaults to no-op if not
> used.
>
> arch/riscv/include/asm/elf.h | 1 +
> fs/binfmt_elf.c | 34 ++++++++++++++++++++++++++++------
> include/linux/mm_types.h | 3 +++
> 3 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> index c7aea7886d22..5d9f0ac851ee 100644
> --- a/arch/riscv/include/asm/elf.h
> +++ b/arch/riscv/include/asm/elf.h
> @@ -20,6 +20,7 @@
> * These are used to set parameters in the core dumps.
> */
> #define ELF_ARCH EM_RISCV
> +#define ELF_CORE_USE_PROCESS_EFLAGS
Let's move this to the per-arch Kconfig instead, that way we can use it
in other places. Maybe call in CONFIG_ARCH_HAS_ELF_CORE_EFLAGS?
>
> #ifndef ELF_CLASS
> #ifdef CONFIG_64BIT
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index caeddccaa1fe..e52b1e077218 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -66,6 +66,14 @@
> #define elf_check_fdpic(ex) false
> #endif
>
> +#ifdef ELF_CORE_USE_PROCESS_EFLAGS
> +#define elf_coredump_get_process_eflags(dump_task, e_flags) \
> + (*(e_flags) = (dump_task)->mm->saved_e_flags)
> +#else
> +#define elf_coredump_get_process_eflags(dump_task, e_flags) \
> + do { (void)(dump_task); (void)(e_flags); } while (0)
> +#endif
Let's make specific set/get helpers here, instead.
static inline
u32 coredump_get_mm_eflags(struct mm_struct *mm, u32 flags)
{
#ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS
flags = mm->saved_e_flags;
#else
return flags;
}
static inline
void coredump_set_mm_eflags(struct mm_struct *mm, u32 flags)
{
#ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS
mm->saved_e_flags = flags;
#endif
}
> +
> static int load_elf_binary(struct linux_binprm *bprm);
>
> /*
> @@ -1290,6 +1298,9 @@ static int load_elf_binary(struct linux_binprm *bprm)
> mm->end_data = end_data;
> mm->start_stack = bprm->p;
>
> + /* stash e_flags for use in core dumps */
> + mm->saved_e_flags = elf_ex->e_flags;
Then this is:
coredump_set_mm_eflags(mm, elf_ex->e_flags);
> +
> /**
> * DOC: "brk" handling
> *
> @@ -1804,6 +1815,8 @@ 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 +1844,26 @@ 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
>
> + /*
> + * Override ELF e_flags with value taken from process,
> + * if arch wants to.
> + */
> + elf_coredump_get_process_eflags(dump_task, &flags);
And this is:
flags = coredump_get_mm_eflags(dump_task->mm, flags);
> +
> + /*
> + * 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..e46f554f8d91 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1098,6 +1098,9 @@ struct mm_struct {
>
> unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
>
And then add:
#ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS
> + /* the ABI-related flags from the ELF header. Used for core dump */
> + unsigned long saved_e_flags;
#endif
around this part
> +
> struct percpu_counter rss_stat[NR_MM_COUNTERS];
>
> struct linux_binfmt *binfmt;
> --
> 2.50.1
>
--
Kees Cook
