diff mbox series

[v16,15/16] arm64: kexec_file: add kernel signature verification support

Message ID 20181115055254.2812-16-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 Nov. 15, 2018, 5:52 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>
Reviewed-by: James Morse <james.morse@arm.com>
---
 arch/arm64/Kconfig              | 24 ++++++++++++++++++++++++
 arch/arm64/kernel/kexec_image.c | 17 +++++++++++++++++
 2 files changed, 41 insertions(+)

Comments

Will Deacon Nov. 30, 2018, 1:21 p.m. UTC | #1
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
AKASHI Takahiro Dec. 11, 2018, 5:42 a.m. UTC | #2
On Fri, Nov 30, 2018 at 01:21:14PM +0000, Will Deacon wrote:
> 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.

This line comes from kexec-tools' code, but I don't mind removing it.
(as lots of lines diverge now from kexec-tools.)

-Takahiro Akashi


> Will
diff mbox series

Patch

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
 };