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

Commit Message

Thiago Jung Bauermann June 28, 2019, 2:19 a.m. UTC

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 <[e-mail]>
Reviewed-by: Mimi Zohar <[e-mail]>
Cc: Jessica Yu <[e-mail]>
---
 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(-)

Comments

Jessica Yu July 1, 2019, 2:47 p.m. UTC | #1

+++ 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 <[e-mail]>
>Reviewed-by: Mimi Zohar <[e-mail]>
>Cc: Jessica Yu <[e-mail]>
>---
> 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 <[e-mail]>

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 ([e-mail])
>+ */
>+
>+#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 ([e-mail])
>+ */
>+
>+#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
>

Thiago Jung Bauermann July 4, 2019, 6:42 a.m. UTC | #2

Jessica Yu <[e-mail]> writes:

> +++ 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 <[e-mail]>
>>Reviewed-by: Mimi Zohar <[e-mail]>
>>Cc: Jessica Yu <[e-mail]>
>>---
>> 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.

Hello Jessica, thanks for reviewing the patch!

> 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.

Indeed. Thanks for spotting that. The patch below fixes it. It's
identical to the previous version except for the changes in 
arch/s390/kernel/machine_kexec_file.c and their description in the
commit message. I'm also copying some s390 people in this email.

> Other than that, the module-related changes look good to me:
>
> Acked-by: Jessica Yu <[e-mail]>

Thank you very much!

Philipp Rudo July 4, 2019, 10:54 a.m. UTC | #3

Hi Thiago,


On Thu, 04 Jul 2019 03:42:57 -0300
Thiago Jung Bauermann <[e-mail]> wrote:

> Jessica Yu <[e-mail]> writes:
> 
> > +++ 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 <[e-mail]>
> >>Reviewed-by: Mimi Zohar <[e-mail]>
> >>Cc: Jessica Yu <[e-mail]>
> >>---
> >> 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.  
> 
> Hello Jessica, thanks for reviewing the patch!
> 
> > 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.  
> 
> Indeed. Thanks for spotting that. The patch below fixes it. It's
> identical to the previous version except for the changes in 
> arch/s390/kernel/machine_kexec_file.c and their description in the
> commit message. I'm also copying some s390 people in this email.

to me the s390 part looks good but for one minor nit.

In arch/s390/Kconfig KEXEC_VERIFY_SIG currently depends on
SYSTEM_DATA_VERIFICATION. I'd prefer when you update this to the new
MODULE_SIG_FORMAT. It shouldn't make any difference right now, as we don't
use mod_check_sig in our code path. But it could cause problems in the future,
when more code might be shared.

Thanks
Philipp

> > Other than that, the module-related changes look good to me:
> >
> > Acked-by: Jessica Yu <[e-mail]>  
> 
> Thank you very much!
>

Thiago Jung Bauermann July 4, 2019, 6:57 p.m. UTC | #4

Hello Philipp,

Philipp Rudo <[e-mail]> writes:

> Hi Thiago,
>
>
> On Thu, 04 Jul 2019 03:42:57 -0300
> Thiago Jung Bauermann <[e-mail]> wrote:
>
>> Jessica Yu <[e-mail]> writes:
>> 
>> > +++ 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 <[e-mail]>
>> >>Reviewed-by: Mimi Zohar <[e-mail]>
>> >>Cc: Jessica Yu <[e-mail]>
>> >>---
>> >> 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.  
>> 
>> Hello Jessica, thanks for reviewing the patch!
>> 
>> > 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.  
>> 
>> Indeed. Thanks for spotting that. The patch below fixes it. It's
>> identical to the previous version except for the changes in 
>> arch/s390/kernel/machine_kexec_file.c and their description in the
>> commit message. I'm also copying some s390 people in this email.
>
> to me the s390 part looks good but for one minor nit.

Thanks for the prompt review!

> In arch/s390/Kconfig KEXEC_VERIFY_SIG currently depends on
> SYSTEM_DATA_VERIFICATION. I'd prefer when you update this to the new
> MODULE_SIG_FORMAT. It shouldn't make any difference right now, as we don't
> use mod_check_sig in our code path. But it could cause problems in the future,
> when more code might be shared.

Makes sense. Here is the updated patch with the Kconfig change.

Philipp Rudo July 5, 2019, 1 p.m. UTC | #5

Hi Thiago,

On Thu, 04 Jul 2019 15:57:34 -0300
Thiago Jung Bauermann <[e-mail]> wrote:

> Hello Philipp,
> 
> Philipp Rudo <[e-mail]> writes:
> 
> > Hi Thiago,
> >
> >
> > On Thu, 04 Jul 2019 03:42:57 -0300
> > Thiago Jung Bauermann <[e-mail]> wrote:
> >  
> >> Jessica Yu <[e-mail]> writes:
> >>   
> >> > +++ 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 <[e-mail]>
> >> >>Reviewed-by: Mimi Zohar <[e-mail]>
> >> >>Cc: Jessica Yu <[e-mail]>
> >> >>---
> >> >> 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.    
> >> 
> >> Hello Jessica, thanks for reviewing the patch!
> >>   
> >> > 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.    
> >> 
> >> Indeed. Thanks for spotting that. The patch below fixes it. It's
> >> identical to the previous version except for the changes in 
> >> arch/s390/kernel/machine_kexec_file.c and their description in the
> >> commit message. I'm also copying some s390 people in this email.  
> >
> > to me the s390 part looks good but for one minor nit.  
> 
> Thanks for the prompt review!
> 
> > In arch/s390/Kconfig KEXEC_VERIFY_SIG currently depends on
> > SYSTEM_DATA_VERIFICATION. I'd prefer when you update this to the new
> > MODULE_SIG_FORMAT. It shouldn't make any difference right now, as we don't
> > use mod_check_sig in our code path. But it could cause problems in the future,
> > when more code might be shared.  
> 
> Makes sense. Here is the updated patch with the Kconfig change.
> 

The patch looks good now.

Thanks a lot
PHilipp

Thiago Jung Bauermann July 23, 2019, 10:39 p.m. UTC | #6

Hello Philipp,


Philipp Rudo <[e-mail]> writes:

> Hi Thiago,
>
> On Thu, 04 Jul 2019 15:57:34 -0300
> Thiago Jung Bauermann <[e-mail]> wrote:
>
>> Hello Philipp,
>> 
>> Philipp Rudo <[e-mail]> writes:
>> 
>> > Hi Thiago,
>> >
>> >
>> > On Thu, 04 Jul 2019 03:42:57 -0300
>> > Thiago Jung Bauermann <[e-mail]> wrote:
>> >  
>> >> Jessica Yu <[e-mail]> writes:
>> >>   
>> >> > +++ 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 <[e-mail]>
>> >> >>Reviewed-by: Mimi Zohar <[e-mail]>
>> >> >>Cc: Jessica Yu <[e-mail]>
>> >> >>---
>> >> >> 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.    
>> >> 
>> >> Hello Jessica, thanks for reviewing the patch!
>> >>   
>> >> > 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.    
>> >> 
>> >> Indeed. Thanks for spotting that. The patch below fixes it. It's
>> >> identical to the previous version except for the changes in 
>> >> arch/s390/kernel/machine_kexec_file.c and their description in the
>> >> commit message. I'm also copying some s390 people in this email.  
>> >
>> > to me the s390 part looks good but for one minor nit.  
>> 
>> Thanks for the prompt review!
>> 
>> > In arch/s390/Kconfig KEXEC_VERIFY_SIG currently depends on
>> > SYSTEM_DATA_VERIFICATION. I'd prefer when you update this to the new
>> > MODULE_SIG_FORMAT. It shouldn't make any difference right now, as we don't
>> > use mod_check_sig in our code path. But it could cause problems in the future,
>> > when more code might be shared.  
>> 
>> Makes sense. Here is the updated patch with the Kconfig change.
>> 
>
> The patch looks good now.

Thanks! Can I add your Reviewed-by?

Philipp Rudo Aug. 5, 2019, 1:11 p.m. UTC | #7

Hi Thiago,

> > The patch looks good now.  
> 
> Thanks! Can I add your Reviewed-by?

sorry, for the late answer, but I was on vacation the last two weeks. I hope
it's not too late now.

Reviewed-by: Philipp Rudo <[e-mail]>

Mimi Zohar Aug. 5, 2019, 2:25 p.m. UTC | #8

On Mon, 2019-08-05 at 15:11 +0200, Philipp Rudo wrote:
> Hi Thiago,
> 
> > > The patch looks good now.  
> > 
> > Thanks! Can I add your Reviewed-by?
> 
> sorry, for the late answer, but I was on vacation the last two weeks. I hope
> it's not too late now.
> 
> Reviewed-by: Philipp Rudo <[e-mail]>

Thanks!  This patch set is still in the #next-queued-testing
branch.  I'm still hoping for a few more tags, before pushing it out
to the #next-integrity branch later today.

Mimi

Patch

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"
-
 /* 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 ([e-mail])
+ */
+
+#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 ([e-mail])
+ */
+
+#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