Re: [PATCH v12 01/11] MODSIGN: Export module signature definitions

[Jessica Yu]

+++ Thiago Jung Bauermann [27/06/19 23:19 -0300]:
> IMA will use the module_signature format for append signatures, so export
> the relevant definitions and factor out the code which verifies that the
> appended signature trailer is valid.
>
> Also, create a CONFIG_MODULE_SIG_FORMAT option so that IMA can select it
> and be able to use mod_check_sig() without having to depend on either
> CONFIG_MODULE_SIG or CONFIG_MODULES.
>
> Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> ---
> include/linux/module.h           |  3 --
> include/linux/module_signature.h | 44 +++++++++++++++++++++++++
> init/Kconfig                     |  6 +++-
> kernel/Makefile                  |  1 +
> kernel/module.c                  |  1 +
> kernel/module_signature.c        | 46 ++++++++++++++++++++++++++
> kernel/module_signing.c          | 56 +++++---------------------------
> scripts/Makefile                 |  2 +-
> 8 files changed, 106 insertions(+), 53 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 188998d3dca9..aa56f531cf1e 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -25,9 +25,6 @@
> #include <linux/percpu.h>
> #include <asm/module.h>
>
> -/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
> -#define MODULE_SIG_STRING "~Module signature appended~\n"
> -

Hi Thiago, apologies for the delay.

It looks like arch/s390/kernel/machine_kexec_file.c also relies on
MODULE_SIG_STRING being defined, so module_signature.h will need to be
included there too, otherwise we'll run into a compilation error.

Other than that, the module-related changes look good to me:

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thanks!

Jessica

> /* Not Yet Implemented */
> #define MODULE_SUPPORTED_DEVICE(name)
>
> diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h
> new file mode 100644
> index 000000000000..523617fc5b6a
> --- /dev/null
> +++ b/include/linux/module_signature.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Module signature handling.
> + *
> + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@xxxxxxxxxx)
> + */
> +
> +#ifndef _LINUX_MODULE_SIGNATURE_H
> +#define _LINUX_MODULE_SIGNATURE_H
> +
> +/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
> +#define MODULE_SIG_STRING "~Module signature appended~\n"
> +
> +enum pkey_id_type {
> +	PKEY_ID_PGP,		/* OpenPGP generated key ID */
> +	PKEY_ID_X509,		/* X.509 arbitrary subjectKeyIdentifier */
> +	PKEY_ID_PKCS7,		/* Signature in PKCS#7 message */
> +};
> +
> +/*
> + * Module signature information block.
> + *
> + * The constituents of the signature section are, in order:
> + *
> + *	- Signer's name
> + *	- Key identifier
> + *	- Signature data
> + *	- Information block
> + */
> +struct module_signature {
> +	u8	algo;		/* Public-key crypto algorithm [0] */
> +	u8	hash;		/* Digest algorithm [0] */
> +	u8	id_type;	/* Key identifier type [PKEY_ID_PKCS7] */
> +	u8	signer_len;	/* Length of signer's name [0] */
> +	u8	key_id_len;	/* Length of key identifier [0] */
> +	u8	__pad[3];
> +	__be32	sig_len;	/* Length of signature data */
> +};
> +
> +int mod_check_sig(const struct module_signature *ms, size_t file_len,
> +		  const char *name);
> +
> +#endif /* _LINUX_MODULE_SIGNATURE_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index 8b9ffe236e4f..c2286a3c74c5 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1852,6 +1852,10 @@ config BASE_SMALL
> 	default 0 if BASE_FULL
> 	default 1 if !BASE_FULL
>
> +config MODULE_SIG_FORMAT
> +	def_bool n
> +	select SYSTEM_DATA_VERIFICATION
> +
> menuconfig MODULES
> 	bool "Enable loadable module support"
> 	option modules
> @@ -1929,7 +1933,7 @@ config MODULE_SRCVERSION_ALL
> config MODULE_SIG
> 	bool "Module signature verification"
> 	depends on MODULES
> -	select SYSTEM_DATA_VERIFICATION
> +	select MODULE_SIG_FORMAT
> 	help
> 	  Check modules for valid signatures upon load: the signature
> 	  is simply appended to the module. For more information see
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 33824f0385b3..f29ae2997a43 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -58,6 +58,7 @@ endif
> obj-$(CONFIG_UID16) += uid16.o
> obj-$(CONFIG_MODULES) += module.o
> obj-$(CONFIG_MODULE_SIG) += module_signing.o
> +obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signature.o
> obj-$(CONFIG_KALLSYMS) += kallsyms.o
> obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
> obj-$(CONFIG_CRASH_CORE) += crash_core.o
> diff --git a/kernel/module.c b/kernel/module.c
> index 6e6712b3aaf5..2712f4d217f5 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -19,6 +19,7 @@
> #include <linux/export.h>
> #include <linux/extable.h>
> #include <linux/moduleloader.h>
> +#include <linux/module_signature.h>
> #include <linux/trace_events.h>
> #include <linux/init.h>
> #include <linux/kallsyms.h>
> diff --git a/kernel/module_signature.c b/kernel/module_signature.c
> new file mode 100644
> index 000000000000..4224a1086b7d
> --- /dev/null
> +++ b/kernel/module_signature.c
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Module signature checker
> + *
> + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@xxxxxxxxxx)
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/printk.h>
> +#include <linux/module_signature.h>
> +#include <asm/byteorder.h>
> +
> +/**
> + * mod_check_sig - check that the given signature is sane
> + *
> + * @ms:		Signature to check.
> + * @file_len:	Size of the file to which @ms is appended.
> + * @name:	What is being checked. Used for error messages.
> + */
> +int mod_check_sig(const struct module_signature *ms, size_t file_len,
> +		  const char *name)
> +{
> +	if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
> +		return -EBADMSG;
> +
> +	if (ms->id_type != PKEY_ID_PKCS7) {
> +		pr_err("%s: Module is not signed with expected PKCS#7 message\n",
> +		       name);
> +		return -ENOPKG;
> +	}
> +
> +	if (ms->algo != 0 ||
> +	    ms->hash != 0 ||
> +	    ms->signer_len != 0 ||
> +	    ms->key_id_len != 0 ||
> +	    ms->__pad[0] != 0 ||
> +	    ms->__pad[1] != 0 ||
> +	    ms->__pad[2] != 0) {
> +		pr_err("%s: PKCS#7 signature info has unexpected non-zero params\n",
> +		       name);
> +		return -EBADMSG;
> +	}
> +
> +	return 0;
> +}
> diff --git a/kernel/module_signing.c b/kernel/module_signing.c
> index 6b9a926fd86b..cdd04a6b8074 100644
> --- a/kernel/module_signing.c
> +++ b/kernel/module_signing.c
> @@ -11,37 +11,13 @@
>
> #include <linux/kernel.h>
> #include <linux/errno.h>
> +#include <linux/module.h>
> +#include <linux/module_signature.h>
> #include <linux/string.h>
> #include <linux/verification.h>
> #include <crypto/public_key.h>
> #include "module-internal.h"
>
> -enum pkey_id_type {
> -	PKEY_ID_PGP,		/* OpenPGP generated key ID */
> -	PKEY_ID_X509,		/* X.509 arbitrary subjectKeyIdentifier */
> -	PKEY_ID_PKCS7,		/* Signature in PKCS#7 message */
> -};
> -
> -/*
> - * Module signature information block.
> - *
> - * The constituents of the signature section are, in order:
> - *
> - *	- Signer's name
> - *	- Key identifier
> - *	- Signature data
> - *	- Information block
> - */
> -struct module_signature {
> -	u8	algo;		/* Public-key crypto algorithm [0] */
> -	u8	hash;		/* Digest algorithm [0] */
> -	u8	id_type;	/* Key identifier type [PKEY_ID_PKCS7] */
> -	u8	signer_len;	/* Length of signer's name [0] */
> -	u8	key_id_len;	/* Length of key identifier [0] */
> -	u8	__pad[3];
> -	__be32	sig_len;	/* Length of signature data */
> -};
> -
> /*
>  * Verify the signature on a module.
>  */
> @@ -49,6 +25,7 @@ int mod_verify_sig(const void *mod, struct load_info *info)
> {
> 	struct module_signature ms;
> 	size_t sig_len, modlen = info->len;
> +	int ret;
>
> 	pr_devel("==>%s(,%zu)\n", __func__, modlen);
>
> @@ -56,32 +33,15 @@ int mod_verify_sig(const void *mod, struct load_info *info)
> 		return -EBADMSG;
>
> 	memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
> -	modlen -= sizeof(ms);
> +
> +	ret = mod_check_sig(&ms, modlen, info->name);
> +	if (ret)
> +		return ret;
>
> 	sig_len = be32_to_cpu(ms.sig_len);
> -	if (sig_len >= modlen)
> -		return -EBADMSG;
> -	modlen -= sig_len;
> +	modlen -= sig_len + sizeof(ms);
> 	info->len = modlen;
>
> -	if (ms.id_type != PKEY_ID_PKCS7) {
> -		pr_err("%s: Module is not signed with expected PKCS#7 message\n",
> -		       info->name);
> -		return -ENOPKG;
> -	}
> -
> -	if (ms.algo != 0 ||
> -	    ms.hash != 0 ||
> -	    ms.signer_len != 0 ||
> -	    ms.key_id_len != 0 ||
> -	    ms.__pad[0] != 0 ||
> -	    ms.__pad[1] != 0 ||
> -	    ms.__pad[2] != 0) {
> -		pr_err("%s: PKCS#7 signature info has unexpected non-zero params\n",
> -		       info->name);
> -		return -EBADMSG;
> -	}
> -
> 	return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
> 				      VERIFY_USE_SECONDARY_KEYRING,
> 				      VERIFYING_MODULE_SIGNATURE,
> diff --git a/scripts/Makefile b/scripts/Makefile
> index 9d442ee050bd..52098b080ab7 100644
> --- a/scripts/Makefile
> +++ b/scripts/Makefile
> @@ -17,7 +17,7 @@ hostprogs-$(CONFIG_VT)           += conmakehash
> hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
> hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
> hostprogs-$(CONFIG_ASN1)	 += asn1_compiler
> -hostprogs-$(CONFIG_MODULE_SIG)	 += sign-file
> +hostprogs-$(CONFIG_MODULE_SIG_FORMAT) += sign-file
> hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert
> hostprogs-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE) += insert-sys-cert