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Message-Id: <1520615434.3911.3.camel@linux.vnet.ibm.com>
Date: Fri, 09 Mar 2018 12:10:34 -0500
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Nayna Jain <nayna@...ux.vnet.ibm.com>, dhowells@...hat.com
Cc: keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org
Subject: Re: [PATCH v2 1/3] certs: define a trusted platform keyring
On Fri, 2018-03-09 at 21:08 +0530, Nayna Jain wrote:
> The kernel can be supplied in SEEPROM or lockable flash memory in embedded
> devices. Some devices may not support secure boot, but the kernel is
> trusted because the image is stored in protected memory. That kernel may
> need to kexec additional kernels, it may be used as a bootloader, for
> example, or it may need to kexec a crashdump kernel. In such cases, it may
> want to verify the signature of the next kernel.
>
> The kernel, however, cannot directly verify platform keys, and an
> administrator may therefore not want to trust them for arbitrary usage.
> In order to differentiate platform keys from other keys and provide the
> necessary separation of trust, the kernel needs an additional keyring to
> store platform keys.
>
> This patch implements a built-in list of certificates that are loaded onto
> the trusted platform keyring named ".platform_keys" to facilitate signature
> verification during kexec. Because the platform keyring are builtin, it
> cannot be updated from userspace.
>
> This keyring can be enabled by setting CONFIG_PLATFORM_KEYRING. The
> platform certificate can be provided using CONFIG_PLATFORM_TRUSTED_KEYS.
>
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
Please add my Reviewed-by: Mimi Zohar <zohar@...ux.vnet.ibm.com> on
this and 2/3.
Mimi
> ---
> Changelog:
>
> v2:
>
> * Include David Howell's feedback:
> * Fix the indentation
> * Fix the patch description per line length as suggested by Mimi
>
> certs/Kconfig | 17 ++++++++++++++
> certs/Makefile | 13 +++++++++++
> certs/system_certificates.S | 20 +++++++++++++++++
> certs/system_keyring.c | 55 ++++++++++++++++++++++++++++++++++++++-------
> 4 files changed, 97 insertions(+), 8 deletions(-)
>
> diff --git a/certs/Kconfig b/certs/Kconfig
> index 5f7663df6e8e..608a4358a25e 100644
> --- a/certs/Kconfig
> +++ b/certs/Kconfig
> @@ -83,4 +83,21 @@ config SYSTEM_BLACKLIST_HASH_LIST
> wrapper to incorporate the list into the kernel. Each <hash> should
> be a string of hex digits.
>
> +config PLATFORM_KEYRING
> + bool "Provide keyring for platform trusted keys"
> + depends on KEYS
> + depends on ASYMMETRIC_KEY_TYPE
> + help
> + Provide a separate, distinct keyring for platform trusted keys, which
> + the kernel automatically populates during initialization from values
> + embedded during build, used for verifying the kexec'ed kernel image
> + and, possibly, the initramfs signature.
> +
> +config PLATFORM_TRUSTED_KEYS
> + string "Platform/Firmware trusted X.509 certs."
> + depends on PLATFORM_KEYRING
> + help
> + Provide the filename of a PEM-formatted file containing the platform
> + trusted X.509 certificates to be loaded in the platform keyring.
> +
> endmenu
> diff --git a/certs/Makefile b/certs/Makefile
> index 5d0999b9e21b..680903725031 100644
> --- a/certs/Makefile
> +++ b/certs/Makefile
> @@ -104,3 +104,16 @@ targets += signing_key.x509
> $(obj)/signing_key.x509: scripts/extract-cert $(X509_DEP) FORCE
> $(call if_changed,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
> endif # CONFIG_MODULE_SIG
> +
> +
> +ifeq ($(CONFIG_PLATFORM_KEYRING),y)
> +
> +$(eval $(call config_filename,PLATFORM_TRUSTED_KEYS))
> +
> +# GCC doesn't include .incbin files in -MD generated dependencies (PR#66871)
> +$(obj)/system_certificates.o: $(obj)/platform_certificate_list
> +
> +targets += platform_certificate_list
> +$(obj)/platform_certificate_list: scripts/extract-cert $(PLATFORM_TRUSTED_KEYS_FILENAME) FORCE
> + $(call if_changed,extract_certs,$(CONFIG_PLATFORM_TRUSTED_KEYS))
> +endif # CONFIG_PLATFORM_KEYRING
> diff --git a/certs/system_certificates.S b/certs/system_certificates.S
> index 3918ff7235ed..b0eb448ee617 100644
> --- a/certs/system_certificates.S
> +++ b/certs/system_certificates.S
> @@ -14,6 +14,15 @@ __cert_list_start:
> .incbin "certs/x509_certificate_list"
> __cert_list_end:
>
> +#ifdef CONFIG_PLATFORM_KEYRING
> + .align 8
> + .globl VMLINUX_SYMBOL(platform_certificate_list)
> +VMLINUX_SYMBOL(platform_certificate_list):
> +__platform_cert_list_start:
> + .incbin "certs/platform_certificate_list"
> +__platform_cert_list_end:
> +#endif /* CONFIG_PLATFORM_KEYRING */
> +
> #ifdef CONFIG_SYSTEM_EXTRA_CERTIFICATE
> .globl VMLINUX_SYMBOL(system_extra_cert)
> .size system_extra_cert, CONFIG_SYSTEM_EXTRA_CERTIFICATE_SIZE
> @@ -35,3 +44,14 @@ VMLINUX_SYMBOL(system_certificate_list_size):
> #else
> .long __cert_list_end - __cert_list_start
> #endif
> +
> +#ifdef CONFIG_PLATFORM_KEYRING
> + .align 8
> + .globl VMLINUX_SYMBOL(platform_certificate_list_size)
> +VMLINUX_SYMBOL(platform_certificate_list_size):
> +#ifdef CONFIG_64BIT
> + .quad __platform_cert_list_end - __platform_cert_list_start
> +#else
> + .long __platform_cert_list_end - __platform_cert_list_start
> +#endif
> +#endif /* CONFIG_PLATFORM_KEYRING */
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index 6251d1b27f0c..594b4986a081 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -19,14 +19,22 @@
> #include <keys/system_keyring.h>
> #include <crypto/pkcs7.h>
>
> +#define BUILTIN_TRUSTED_KEYRING 0
> +#define PLATFORM_KEYRING 1
> +
> static struct key *builtin_trusted_keys;
> #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
> static struct key *secondary_trusted_keys;
> #endif
> +#ifdef CONFIG_PLATFORM_KEYRING
> +static struct key *platform_keys __ro_after_init;
> +#endif
>
> extern __initconst const u8 system_certificate_list[];
> extern __initconst const unsigned long system_certificate_list_size;
>
> +extern __initconst const u8 platform_certificate_list[];
> +extern __initconst const unsigned long platform_certificate_list_size;
> /**
> * restrict_link_to_builtin_trusted - Restrict keyring addition by built in CA
> *
> @@ -123,6 +131,18 @@ static __init int system_trusted_keyring_init(void)
> panic("Can't link trusted keyrings\n");
> #endif
>
> +#ifdef CONFIG_PLATFORM_KEYRING
> + platform_keys =
> + keyring_alloc(".platform_keys",
> + KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
> + ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
> + KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH),
> + KEY_ALLOC_NOT_IN_QUOTA,
> + NULL, NULL);
> + if (IS_ERR(platform_keys))
> + panic("Can't allocate platform keyring\n");
> +#endif
> +
> return 0;
> }
>
> @@ -132,18 +152,19 @@ static __init int system_trusted_keyring_init(void)
> device_initcall(system_trusted_keyring_init);
>
> /*
> - * Load the compiled-in list of X.509 certificates.
> + * Load the certificates to the keyring.
> */
> -static __init int load_system_certificate_list(void)
> +static __init int load_certificate_list(const u8 *p, unsigned long size,
> + struct key *keyring)
> {
> key_ref_t key;
> - const u8 *p, *end;
> + const u8 *end;
> size_t plen;
>
> - pr_notice("Loading compiled-in X.509 certificates\n");
> + pr_notice("Loading compiled-in X.509 certificates to %s\n",
> + keyring->description);
>
> - p = system_certificate_list;
> - end = p + system_certificate_list_size;
> + end = p + size;
> while (p < end) {
> /* Each cert begins with an ASN.1 SEQUENCE tag and must be more
> * than 256 bytes in size.
> @@ -158,7 +179,7 @@ static __init int load_system_certificate_list(void)
> if (plen > end - p)
> goto dodgy_cert;
>
> - key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),
> + key = key_create_or_update(make_key_ref(keyring, 1),
> "asymmetric",
> NULL,
> p,
> @@ -185,7 +206,25 @@ static __init int load_system_certificate_list(void)
> pr_err("Problem parsing in-kernel X.509 certificate list\n");
> return 0;
> }
> -late_initcall(load_system_certificate_list);
> +
> +/*
> + * Load the compiled-in list of system and platform X.509 certificates.
> + */
> +static __init int load_compiled_certificate_list(void)
> +{
> + /* Loading certs in builtin keyring */
> + load_certificate_list(system_certificate_list,
> + system_certificate_list_size, builtin_trusted_keys);
> +
> +#ifdef CONFIG_PLATFORM_KEYRING
> + /* Loading certs in platform keyring */
> + load_certificate_list(platform_certificate_list,
> + platform_certificate_list_size, platform_keys);
> +#endif
> +
> + return 0;
> +}
> +late_initcall(load_compiled_certificate_list);
>
> #ifdef CONFIG_SYSTEM_DATA_VERIFICATION
>
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