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    Subject[PATCH v7 04/11] elf: Allow arch to tweak initial mmap prot flags
    Date
    From: Dave Martin <Dave.Martin@arm.com>

    An arch may want to tweak the mmap prot flags for an
    ELFexecutable's initial mappings. For example, arm64 is going to
    need to add PROT_BTI for executable pages in an ELF process whose
    executable is marked as using Branch Target Identification (an
    ARMv8.5-A control flow integrity feature).

    So that this can be done in a generic way, add a hook
    arch_elf_adjust_prot() to modify the prot flags as desired: arches
    can select CONFIG_HAVE_ELF_PROT and implement their own backend
    where necessary.

    By default, leave the prot flags unchanged.

    Signed-off-by: Dave Martin <Dave.Martin@arm.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Mark Brown <broonie@kernel.org>
    ---
    fs/Kconfig.binfmt | 3 +++
    fs/binfmt_elf.c | 18 ++++++++++++------
    include/linux/elf.h | 12 ++++++++++++
    3 files changed, 27 insertions(+), 6 deletions(-)

    diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
    index d2cfe0729a73..2358368319b8 100644
    --- a/fs/Kconfig.binfmt
    +++ b/fs/Kconfig.binfmt
    @@ -36,6 +36,9 @@ config COMPAT_BINFMT_ELF
    config ARCH_BINFMT_ELF_STATE
    bool

    +config ARCH_HAVE_ELF_PROT
    + bool
    +
    config ARCH_USE_GNU_PROPERTY
    bool

    diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
    index 1fb67e506b68..cceb29d6ef1d 100644
    --- a/fs/binfmt_elf.c
    +++ b/fs/binfmt_elf.c
    @@ -544,7 +544,8 @@ static inline int arch_check_elf(struct elfhdr *ehdr, bool has_interp,

    #endif /* !CONFIG_ARCH_BINFMT_ELF_STATE */

    -static inline int make_prot(u32 p_flags)
    +static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
    + bool has_interp, bool is_interp)
    {
    int prot = 0;

    @@ -554,7 +555,8 @@ static inline int make_prot(u32 p_flags)
    prot |= PROT_WRITE;
    if (p_flags & PF_X)
    prot |= PROT_EXEC;
    - return prot;
    +
    + return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
    }

    /* This is much more generalized than the library routine read function,
    @@ -564,7 +566,8 @@ static inline int make_prot(u32 p_flags)

    static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
    struct file *interpreter,
    - unsigned long no_base, struct elf_phdr *interp_elf_phdata)
    + unsigned long no_base, struct elf_phdr *interp_elf_phdata,
    + struct arch_elf_state *arch_state)
    {
    struct elf_phdr *eppnt;
    unsigned long load_addr = 0;
    @@ -596,7 +599,8 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
    for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
    if (eppnt->p_type == PT_LOAD) {
    int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
    - int elf_prot = make_prot(eppnt->p_flags);
    + int elf_prot = make_prot(eppnt->p_flags, arch_state,
    + true, true);
    unsigned long vaddr = 0;
    unsigned long k, map_addr;

    @@ -1041,7 +1045,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
    }
    }

    - elf_prot = make_prot(elf_ppnt->p_flags);
    + elf_prot = make_prot(elf_ppnt->p_flags, &arch_state,
    + !!interpreter, false);

    elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;

    @@ -1184,7 +1189,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
    if (interpreter) {
    elf_entry = load_elf_interp(&loc->interp_elf_ex,
    interpreter,
    - load_bias, interp_elf_phdata);
    + load_bias, interp_elf_phdata,
    + &arch_state);
    if (!IS_ERR((void *)elf_entry)) {
    /*
    * load_elf_interp() returns relocation
    diff --git a/include/linux/elf.h b/include/linux/elf.h
    index db5113479f5e..5d5b0321da0b 100644
    --- a/include/linux/elf.h
    +++ b/include/linux/elf.h
    @@ -87,4 +87,16 @@ extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
    bool compat, struct arch_elf_state *arch);
    #endif

    +#ifdef CONFIG_ARCH_HAVE_ELF_PROT
    +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
    + bool has_interp, bool is_interp);
    +#else
    +static inline int arch_elf_adjust_prot(int prot,
    + const struct arch_elf_state *state,
    + bool has_interp, bool is_interp)
    +{
    + return prot;
    +}
    +#endif
    +
    #endif /* _LINUX_ELF_H */
    --
    2.20.1
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