[PATCH v7 11/11] arm64: kexec_file: enable KEXEC_VERIFY_SIG for Image
From: AKASHI Takahiro <hidden>
Date: 2017-12-04 02:56:00
Also in:
kexec, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
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 <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <redacted>
---
arch/arm64/Kconfig | 10 ++++++++++
arch/arm64/include/asm/kexec.h | 16 ++++++++++++++++
arch/arm64/kernel/kexec_image.c | 15 +++++++++++++++
3 files changed, 41 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c0b021736c10..289c7bede593 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig@@ -814,6 +814,16 @@ config KEXEC_FILE_IMAGE_FMT ---help--- Select this option to enable 'Image' kernel loading. +config KEXEC_VERIFY_SIG + bool "Verify kernel signature during kexec_file_load() syscall" + depends on KEXEC_FILE + select SYSTEM_DATA_VERIFICATION + select SIGNED_PE_FILE_VERIFICATION if KEXEC_FILE_IMAGE_FMT + ---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. + config CRASH_DUMP bool "Build kdump crash kernel" help
diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
index b6469bc64a89..2a63bf5f32ea 100644
--- a/arch/arm64/include/asm/kexec.h
+++ b/arch/arm64/include/asm/kexec.h@@ -131,6 +131,7 @@ struct arm64_image_header { }; static const u8 arm64_image_magic[4] = {'A', 'R', 'M', 0x64U}; +static const u8 arm64_image_pe_sig[2] = {'M', 'Z'}; /** * arm64_header_check_magic - Helper to check the arm64 image header.
@@ -152,6 +153,21 @@ static inline int arm64_header_check_magic(const struct arm64_image_header *h) && h->magic[3] == arm64_image_magic[3]); } +/** + * arm64_header_check_pe_sig - Helper to check the arm64 image header. + * + * Returns non-zero if 'MZ' signature is found. + */ + +static inline int arm64_header_check_pe_sig(const struct arm64_image_header *h) +{ + if (!h) + return 0; + + return (h->pe_sig[0] == arm64_image_pe_sig[0] + && h->pe_sig[1] == arm64_image_pe_sig[1]); +} + extern const struct kexec_file_ops kexec_image_ops; struct kimage;
diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
index 1c106237901d..b840b6ed6ed9 100644
--- a/arch/arm64/kernel/kexec_image.c
+++ b/arch/arm64/kernel/kexec_image.c@@ -15,6 +15,7 @@ #include <linux/errno.h> #include <linux/kernel.h> #include <linux/kexec.h> +#include <linux/verification.h> #include <asm/byteorder.h> #include <asm/memory.h>
@@ -27,6 +28,9 @@ static int image_probe(const char *kernel_buf, unsigned long kernel_len) if ((kernel_len < sizeof(*h)) || !arm64_header_check_magic(h)) return -EINVAL; + pr_debug("PE format: %s\n", + (arm64_header_check_pe_sig(h) ? "yes" : "no")); + return 0; }
@@ -84,7 +88,18 @@ static void *image_load(struct kimage *image, char *kernel, return ERR_PTR(ret); } +#ifdef CONFIG_KEXEC_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_VERIFY_SIG + .verify_sig = image_verify_sig, +#endif };
--
2.14.1