Hajime Tazaki <thehajime@xxxxxxxxx> writes:
> As UML supports CONFIG_MMU=n case, it has to use an alternate ELF
> loader, FDPIC ELF loader. In this commit, we added necessary
> definitions in the arch, as UML has not been used so far. It also
> updates Kconfig file to use BINFMT_ELF_FDPIC under !MMU environment.
Why does the no mmu case need an alternative elf loader?
Last time I looked the regular binfmt_elf works just fine
without an mmu. I looked again and at a quick skim the
regular elf loader still looks like it will work without
an MMU.
You would need ET_DYN binaries just so they will load and run
in a position independent way. But even that seems a common
configuration even with a MMU these days.
There are some funny things in elf_fdpic where it departs
from the ELF standard and is no fun to support unless it
is necessary. So I am not excited to see more architectures
supporting ELF_FDPIC.
Eric
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Kees Cook <kees@xxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Christian Brauner <brauner@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Signed-off-by: Hajime Tazaki <thehajime@xxxxxxxxx>
> Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> ---
> arch/um/include/asm/mmu.h | 5 +++++
> arch/um/include/asm/ptrace-generic.h | 6 ++++++
> arch/x86/um/asm/elf.h | 8 ++++++--
> fs/Kconfig.binfmt | 2 +-
> 4 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h
> index a3eaca41ff61..01422b761aa0 100644
> --- a/arch/um/include/asm/mmu.h
> +++ b/arch/um/include/asm/mmu.h
> @@ -14,6 +14,11 @@ typedef struct mm_context {
> /* Address range in need of a TLB sync */
> unsigned long sync_tlb_range_from;
> unsigned long sync_tlb_range_to;
> +
> +#ifdef CONFIG_BINFMT_ELF_FDPIC
> + unsigned long exec_fdpic_loadmap;
> + unsigned long interp_fdpic_loadmap;
> +#endif
> } mm_context_t;
>
> #endif
> diff --git a/arch/um/include/asm/ptrace-generic.h b/arch/um/include/asm/ptrace-generic.h
> index 4696f24d1492..4ff844bcb1cd 100644
> --- a/arch/um/include/asm/ptrace-generic.h
> +++ b/arch/um/include/asm/ptrace-generic.h
> @@ -29,6 +29,12 @@ struct pt_regs {
>
> #define PTRACE_OLDSETOPTIONS 21
>
> +#ifdef CONFIG_BINFMT_ELF_FDPIC
> +#define PTRACE_GETFDPIC 31
> +#define PTRACE_GETFDPIC_EXEC 0
> +#define PTRACE_GETFDPIC_INTERP 1
> +#endif
> +
> struct task_struct;
>
> extern long subarch_ptrace(struct task_struct *child, long request,
> diff --git a/arch/x86/um/asm/elf.h b/arch/x86/um/asm/elf.h
> index 62ed5d68a978..33f69f1eac10 100644
> --- a/arch/x86/um/asm/elf.h
> +++ b/arch/x86/um/asm/elf.h
> @@ -9,6 +9,7 @@
> #include <skas.h>
>
> #define CORE_DUMP_USE_REGSET
> +#define ELF_FDPIC_CORE_EFLAGS 0
>
> #ifdef CONFIG_X86_32
>
> @@ -190,8 +191,11 @@ extern int arch_setup_additional_pages(struct linux_binprm *bprm,
>
> extern unsigned long um_vdso_addr;
> #define AT_SYSINFO_EHDR 33
> -#define ARCH_DLINFO NEW_AUX_ENT(AT_SYSINFO_EHDR, um_vdso_addr)
> -
> +#define ARCH_DLINFO \
> +do { \
> + NEW_AUX_ENT(AT_SYSINFO_EHDR, um_vdso_addr); \
> + NEW_AUX_ENT(AT_MINSIGSTKSZ, 0); \
> +} while (0)
> #endif
>
> typedef unsigned long elf_greg_t;
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index bd2f530e5740..419ba0282806 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -58,7 +58,7 @@ config ARCH_USE_GNU_PROPERTY
> config BINFMT_ELF_FDPIC
> bool "Kernel support for FDPIC ELF binaries"
> default y if !BINFMT_ELF
> - depends on ARM || ((M68K || RISCV || SUPERH || XTENSA) && !MMU)
> + depends on ARM || ((M68K || RISCV || SUPERH || UML || XTENSA) && !MMU)
> select ELFCORE
> help
> ELF FDPIC binaries are based on ELF, but allow the individual load
