diff mbox series

[v12,15/16] arm64: kexec_file: add kernel signature verification support

Message ID 20180724065759.19186-16-takahiro.akashi@linaro.org (mailing list archive)
State New, archived
Headers show
Series arm64: kexec: add kexec_file_load() support | expand

Commit Message

AKASHI Takahiro July 24, 2018, 6:57 a.m. UTC
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>
---
 arch/arm64/Kconfig              | 24 ++++++++++++++++++++++++
 arch/arm64/kernel/kexec_image.c | 15 +++++++++++++++
 2 files changed, 39 insertions(+)

Comments

James Morse July 26, 2018, 1:39 p.m. UTC | #1
Hi Akashi,

On 24/07/18 07:57, 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

Reviewed-by: James Morse <james.morse@arm.com>


> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index d64f5e9f9d22..578d358632d0 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -102,7 +106,18 @@ 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

This is identical to x86's PE image verification helper. We can clean this up
later by providing some kexec_image_verify_pe() in the core kexec_file code. Its
not worth doing now.


>  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
>  };


Thanks,

James
diff mbox series

Patch

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a9a3a5583c8b..1445eb2fc833 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -844,6 +844,30 @@  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 d64f5e9f9d22..578d358632d0 100644
--- a/arch/arm64/kernel/kexec_image.c
+++ b/arch/arm64/kernel/kexec_image.c
@@ -13,6 +13,7 @@ 
 #include <linux/kernel.h>
 #include <linux/kexec.h>
 #include <linux/string.h>
+#include <linux/verification.h>
 #include <asm/boot.h>
 #include <asm/byteorder.h>
 #include <asm/cpufeature.h>
@@ -28,6 +29,9 @@  static int image_probe(const char *kernel_buf, unsigned long kernel_len)
 			memcmp(&h->magic, ARM64_MAGIC, sizeof(h->magic)))
 		return -EINVAL;
 
+	pr_debug("PE format: %s\n",
+			memcmp(&h->mz_magic, "MZ", 2) ?  "no" : "yes");
+
 	return 0;
 }
 
@@ -102,7 +106,18 @@  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
 };