Commit 8c94db0a authored by Svetlana Parfenova's avatar Svetlana Parfenova Committed by Kees Cook
Browse files

binfmt_elf: preserve original ELF e_flags for core dumps 



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()). Kconfig option CONFIG_ARCH_HAS_ELF_CORE_EFLAGS
is introduced for architectures that require this behaviour.

Signed-off-by: default avatarSvetlana Parfenova <svetlana.parfenova@syntacore.com>
Link: https://lore.kernel.org/r/20250901135350.619485-1-svetlana.parfenova@syntacore.com


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent a728ce8f

arch/riscv/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ config RISCV 
	select ARCH_HAS_DEBUG_VIRTUAL if MMU

	select ARCH_HAS_DEBUG_VM_PGTABLE

	select ARCH_HAS_DEBUG_WX

	select ARCH_HAS_ELF_CORE_EFLAGS

	select ARCH_HAS_FAST_MULTIPLIER

	select ARCH_HAS_FORTIFY_SOURCE

	select ARCH_HAS_GCOV_PROFILE_ALL

fs/Kconfig.binfmt

+9 −0
Original line number Diff line number Diff line
@@ -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 ARCH_HAS_ELF_CORE_EFLAGS

	bool

	depends on BINFMT_ELF && ELF_CORE

	default n

	help

	  Select this option if the architecture makes use of the e_flags

	  field in the ELF header to store ABI or other architecture-specific

	  information that should be preserved in core dumps.



endmenu

fs/binfmt_elf.c

+34 −6
Original line number Diff line number Diff line
@@ -103,6 +103,21 @@ static struct linux_binfmt elf_format = { 


#define BAD_ADDR(x) (unlikely((unsigned long)(x) >= TASK_SIZE))



static inline void elf_coredump_set_mm_eflags(struct mm_struct *mm, u32 flags)

{

#ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS

	mm->saved_e_flags = flags;

#endif

}



static inline u32 elf_coredump_get_mm_eflags(struct mm_struct *mm, u32 flags)

{

#ifdef CONFIG_ARCH_HAS_ELF_CORE_EFLAGS

	flags = mm->saved_e_flags;

#endif

	return flags;

}



/*

 * We need to explicitly zero any trailing portion of the page that follows

 * p_filesz when it ends before the page ends (e.g. bss), otherwise this
@@ -1290,6 +1305,8 @@ static int load_elf_binary(struct linux_binprm *bprm) 
	mm->end_data = end_data;

	mm->start_stack = bprm->p;



	elf_coredump_set_mm_eflags(mm, elf_ex->e_flags);



	/**

	 * DOC: "brk" handling

	 *
@@ -1804,6 +1821,8 @@ 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 +1850,26 @@ 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 needs that.

	 */

	flags = elf_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.

	 */

include/linux/mm_types.h

+5 −0
Original line number Diff line number Diff line
@@ -1102,6 +1102,11 @@ struct mm_struct { 


		unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */



#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



		struct percpu_counter rss_stat[NR_MM_COUNTERS];



		struct linux_binfmt *binfmt;