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    Subject[PATCH v1 RFC Zisslpcfi 07/20] elf: ELF header parsing in GNU property for cfi state
    Date
    Binaries enabled with support for control-flow integrity will have new
    instructions that may fault on cpus which dont implement cfi mechanisms.
    This change adds

    - stub for setting up cfi state when loading a binary. Architecture
    specific implementation can choose to implement this stub and setup
    cfi state for program.
    - define riscv ELF flag marker for forward cfi and backward cfi in
    uapi/linux/elf.h

    Signed-off-by: Deepak Gupta <debug@rivosinc.com>
    ---
    fs/binfmt_elf.c | 5 +++++
    include/linux/elf.h | 8 ++++++++
    include/uapi/linux/elf.h | 6 ++++++
    3 files changed, 19 insertions(+)

    diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
    index 9a780fafc539..bb431052eb01 100644
    --- a/fs/binfmt_elf.c
    +++ b/fs/binfmt_elf.c
    @@ -1277,6 +1277,11 @@ static int load_elf_binary(struct linux_binprm *bprm)

    set_binfmt(&elf_format);

    +#if defined(CONFIG_USER_SHADOW_STACK) || defined(CONFIG_USER_INDIRECT_BR_LP)
    + retval = arch_elf_setup_cfi_state(&arch_state);
    + if (retval < 0)
    + goto out;
    +#endif
    #ifdef ARCH_HAS_SETUP_ADDITIONAL_PAGES
    retval = ARCH_SETUP_ADDITIONAL_PAGES(bprm, elf_ex, !!interpreter);
    if (retval < 0)
    diff --git a/include/linux/elf.h b/include/linux/elf.h
    index c9a46c4e183b..106d28f065aa 100644
    --- a/include/linux/elf.h
    +++ b/include/linux/elf.h
    @@ -109,4 +109,12 @@ static inline int arch_elf_adjust_prot(int prot,
    }
    #endif

    +#if defined(CONFIG_USER_SHADOW_STACK) || defined(CONFIG_USER_INDIRECT_BR_LP)
    +extern int arch_elf_setup_cfi_state(const struct arch_elf_state *state);
    +#else
    +static inline int arch_elf_setup_cfi_state(const struct arch_elf_state *state)
    +{
    + return 0;
    +}
    +#endif
    #endif /* _LINUX_ELF_H */
    diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
    index 4c6a8fa5e7ed..1cbd332061dc 100644
    --- a/include/uapi/linux/elf.h
    +++ b/include/uapi/linux/elf.h
    @@ -468,4 +468,10 @@ typedef struct elf64_note {
    /* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */
    #define GNU_PROPERTY_AARCH64_FEATURE_1_BTI (1U << 0)

    +/* .note.gnu.property types for RISCV: */
    +/* Bits for GNU_PROPERTY_RISCV_FEATURE_1_FCFI/BCFI */
    +#define GNU_PROPERTY_RISCV_FEATURE_1_AND 0xc0000000
    +#define GNU_PROPERTY_RISCV_FEATURE_1_FCFI (1u << 0)
    +#define GNU_PROPERTY_RISCV_FEATURE_1_BCFI (1u << 1)
    +
    #endif /* _UAPI_LINUX_ELF_H */
    --
    2.25.1
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