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    SubjectRe: [PATCH v16 15/16] arm64: kexec_file: add kernel signature verification support
    On Thu, Nov 15, 2018 at 02:52:54PM +0900, AKASHI Takahiro wrote:
    > 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");
    >

    Is this hunk really necessary? I'd prefer not to commit pr_debug()
    invocations.

    Will

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