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    Subject[PATCH v16 15/16] arm64: kexec_file: add kernel signature verification support
    Date
    With this patch, kernel verification can be done without IMA security
    subsystem enabled. Turn on CONFIG_KEXEC_VERIFY_SIG instead.

    On x86, a signature is embedded into a PE file (Microsoft's format) header
    of binary. Since arm64's "Image" can also be seen as a PE file as far as
    CONFIG_EFI is enabled, we adopt this format for kernel signing.

    You can create a signed kernel image with:
    $ sbsign --key ${KEY} --cert ${CERT} Image

    Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Reviewed-by: James Morse <james.morse@arm.com>
    ---
    arch/arm64/Kconfig | 24 ++++++++++++++++++++++++
    arch/arm64/kernel/kexec_image.c | 17 +++++++++++++++++
    2 files changed, 41 insertions(+)

    diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    index 93dc4d36d6db..11f3e1a00588 100644
    --- a/arch/arm64/Kconfig
    +++ b/arch/arm64/Kconfig
    @@ -867,6 +867,30 @@ config KEXEC_FILE
    for kernel and initramfs as opposed to list of segments as
    accepted by previous system call.

    +config KEXEC_VERIFY_SIG
    + bool "Verify kernel signature during kexec_file_load() syscall"
    + depends on KEXEC_FILE
    + help
    + Select this option to verify a signature with loaded kernel
    + image. If configured, any attempt of loading a image without
    + valid signature will fail.
    +
    + In addition to that option, you need to enable signature
    + verification for the corresponding kernel image type being
    + loaded in order for this to work.
    +
    +config KEXEC_IMAGE_VERIFY_SIG
    + bool "Enable Image signature verification support"
    + default y
    + depends on KEXEC_VERIFY_SIG
    + depends on EFI && SIGNED_PE_FILE_VERIFICATION
    + help
    + Enable Image signature verification support.
    +
    +comment "Support for PE file signature verification disabled"
    + depends on KEXEC_VERIFY_SIG
    + depends on !EFI || !SIGNED_PE_FILE_VERIFICATION
    +
    config CRASH_DUMP
    bool "Build kdump crash kernel"
    help
    diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
    index 9f0d8b5d62d3..d1c6c54c22e3 100644
    --- a/arch/arm64/kernel/kexec_image.c
    +++ b/arch/arm64/kernel/kexec_image.c
    @@ -12,7 +12,9 @@
    #include <linux/errno.h>
    #include <linux/kernel.h>
    #include <linux/kexec.h>
    +#include <linux/pe.h>
    #include <linux/string.h>
    +#include <linux/verification.h>
    #include <asm/byteorder.h>
    #include <asm/cpufeature.h>
    #include <asm/image.h>
    @@ -29,6 +31,10 @@ static int image_probe(const char *kernel_buf, unsigned long kernel_len)
    sizeof(h->magic)))
    return -EINVAL;

    + pr_debug("PE format: %s\n",
    + memcmp(&((struct mz_hdr *)h)->magic, "MZ", 2) ?
    + "no" : "yes");
    +
    return 0;
    }

    @@ -107,7 +113,18 @@ static void *image_load(struct kimage *image,
    return ERR_PTR(ret);
    }

    +#ifdef CONFIG_KEXEC_IMAGE_VERIFY_SIG
    +static int image_verify_sig(const char *kernel, unsigned long kernel_len)
    +{
    + return verify_pefile_signature(kernel, kernel_len, NULL,
    + VERIFYING_KEXEC_PE_SIGNATURE);
    +}
    +#endif
    +
    const struct kexec_file_ops kexec_image_ops = {
    .probe = image_probe,
    .load = image_load,
    +#ifdef CONFIG_KEXEC_IMAGE_VERIFY_SIG
    + .verify_sig = image_verify_sig,
    +#endif
    };
    --
    2.19.0
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