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    Subject[PATCH v5 12/18] MODSIGN: Export module signature definitions
    Date
    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 validate_module_signature without having to depend on
    CONFIG_MODULE_SIG.

    Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
    ---
    include/linux/module.h | 3 --
    include/linux/module_signature.h | 47 +++++++++++++++++++++++++
    init/Kconfig | 6 +++-
    kernel/Makefile | 2 +-
    kernel/module.c | 1 +
    kernel/module_signing.c | 74 +++++++++++++++++-----------------------
    6 files changed, 85 insertions(+), 48 deletions(-)

    diff --git a/include/linux/module.h b/include/linux/module.h
    index fe5aa3736707..108874af9838 100644
    --- a/include/linux/module.h
    +++ b/include/linux/module.h
    @@ -23,9 +23,6 @@
    #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..e80728e5b86c
    --- /dev/null
    +++ b/include/linux/module_signature.h
    @@ -0,0 +1,47 @@
    +/* Module signature handling.
    + *
    + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
    + * Written by David Howells (dhowells@redhat.com)
    + *
    + * This program is free software; you can redistribute it and/or
    + * modify it under the terms of the GNU General Public Licence
    + * as published by the Free Software Foundation; either version
    + * 2 of the Licence, or (at your option) any later version.
    + */
    +
    +#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 validate_module_sig(const struct module_signature *ms, size_t file_len);
    +int mod_verify_sig(const void *mod, unsigned long *_modlen);
    +
    +#endif /* _LINUX_MODULE_SIGNATURE_H */
    diff --git a/init/Kconfig b/init/Kconfig
    index 78cb2461012e..230e9f3aedaf 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -1748,7 +1748,7 @@ 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
    @@ -1763,6 +1763,10 @@ config MODULE_SIG
    debuginfo strip done by some packagers (such as rpmbuild) and
    inclusion into an initramfs that wants the module size reduced.

    +config MODULE_SIG_FORMAT
    + def_bool n
    + select SYSTEM_DATA_VERIFICATION
    +
    config MODULE_SIG_FORCE
    bool "Require modules to be validly signed"
    depends on MODULE_SIG
    diff --git a/kernel/Makefile b/kernel/Makefile
    index ed470aac53da..20fd6d76232e 100644
    --- a/kernel/Makefile
    +++ b/kernel/Makefile
    @@ -57,7 +57,7 @@ obj-y += up.o
    endif
    obj-$(CONFIG_UID16) += uid16.o
    obj-$(CONFIG_MODULES) += module.o
    -obj-$(CONFIG_MODULE_SIG) += module_signing.o
    +obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signing.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 de66ec825992..a259e9df570d 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_signing.c b/kernel/module_signing.c
    index 937c844bee4a..204c60d4cc9f 100644
    --- a/kernel/module_signing.c
    +++ b/kernel/module_signing.c
    @@ -11,36 +11,38 @@

    #include <linux/kernel.h>
    #include <linux/errno.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:
    +/**
    + * validate_module_sig - validate that the given signature is sane
    *
    - * - Signer's name
    - * - Key identifier
    - * - Signature data
    - * - Information block
    + * @ms: Signature to validate.
    + * @file_len: Size of the file to which @ms is appended.
    */
    -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 validate_module_sig(const struct module_signature *ms, size_t file_len)
    +{
    + if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
    + return -EBADMSG;
    + else if (ms->id_type != PKEY_ID_PKCS7) {
    + pr_err("Module is not signed with expected PKCS#7 message\n");
    + return -ENOPKG;
    + } else 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("PKCS#7 signature info has unexpected non-zero params\n");
    + return -EBADMSG;
    + }
    +
    + return 0;
    +}

    /*
    * Verify the signature on a module.
    @@ -49,6 +51,7 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen)
    {
    struct module_signature ms;
    size_t modlen = *_modlen, sig_len;
    + int ret;

    pr_devel("==>%s(,%zu)\n", __func__, modlen);

    @@ -56,30 +59,15 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen)
    return -EBADMSG;

    memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
    - modlen -= sizeof(ms);
    +
    + ret = validate_module_sig(&ms, modlen);
    + 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);
    *_modlen = modlen;

    - if (ms.id_type != PKEY_ID_PKCS7) {
    - pr_err("Module is not signed with expected PKCS#7 message\n");
    - 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("PKCS#7 signature info has unexpected non-zero params\n");
    - return -EBADMSG;
    - }
    -
    return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
    NULL, VERIFYING_MODULE_SIGNATURE,
    NULL, NULL);
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