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Date: Tue, 20 Apr 2021 14:22:28 +0800
From: joeyli <jlee@...e.com>
To: Varad Gautam <varad.gautam@...e.com>
CC: "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
David Howells <dhowells@...hat.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Ben Boeckel <me@...boeckel.net>,
Randy Dunlap <rdunlap@...radead.org>,
Malte Gell <malte.gell@....de>, keyrings@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] PKCS#7: Check codeSigning EKU for kernel module and
kexec pe verification
Hi Varad,
Thanks for your review!
On Thu, Apr 15, 2021 at 02:08:32PM +0200, Varad Gautam wrote:
> Hi Joey,
>
> On 4/9/21 4:46 AM, Lee, Chun-Yi wrote:
> > This patch adds the logic for checking the CodeSigning extended
> > key usage when verifying signature of kernel module or
> > kexec PE binary in PKCS#7.
> >
> > Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
> > ---
> > certs/system_keyring.c | 2 +-
> > crypto/asymmetric_keys/Kconfig | 9 +++++++++
> > crypto/asymmetric_keys/pkcs7_trust.c | 37 +++++++++++++++++++++++++++++++++---
> > include/crypto/pkcs7.h | 3 ++-
> > 4 files changed, 46 insertions(+), 5 deletions(-)
> >
> > diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> > index 4b693da488f1..c9f8bca0b0d3 100644
> > --- a/certs/system_keyring.c
> > +++ b/certs/system_keyring.c
> > @@ -243,7 +243,7 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
> > goto error;
> > }
> > }
> > - ret = pkcs7_validate_trust(pkcs7, trusted_keys);
> > + ret = pkcs7_validate_trust(pkcs7, trusted_keys, usage);
> > if (ret < 0) {
> > if (ret == -ENOKEY)
> > pr_devel("PKCS#7 signature not signed with a trusted key\n");
> > diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
> > index 1f1f004dc757..1754812df989 100644
> > --- a/crypto/asymmetric_keys/Kconfig
> > +++ b/crypto/asymmetric_keys/Kconfig
> > @@ -96,4 +96,13 @@ config SIGNED_PE_FILE_VERIFICATION
> > This option provides support for verifying the signature(s) on a
> > signed PE binary.
> >
> > +config CHECK_CODESIGN_EKU
> > + bool "Check codeSigning extended key usage"
> > + depends on PKCS7_MESSAGE_PARSER=y
> > + depends on SYSTEM_DATA_VERIFICATION
> > + help
> > + This option provides support for checking the codeSigning extended
> > + key usage when verifying the signature in PKCS#7. It affects kernel
> > + module verification and kexec PE binary verification.
> > +
> > endif # ASYMMETRIC_KEY_TYPE
> > diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
> > index b531df2013c4..077bfef928b6 100644
> > --- a/crypto/asymmetric_keys/pkcs7_trust.c
> > +++ b/crypto/asymmetric_keys/pkcs7_trust.c
> > @@ -16,12 +16,36 @@
> > #include <crypto/public_key.h>
> > #include "pkcs7_parser.h"
> >
> > +#ifdef CONFIG_CHECK_CODESIGN_EKU
> > +static bool check_codesign_eku(struct key *key,
> > + enum key_being_used_for usage)
> > +{
> > + struct public_key *public_key = key->payload.data[asym_crypto];
> > +
> > + switch (usage) {
> > + case VERIFYING_MODULE_SIGNATURE:
> > + case VERIFYING_KEXEC_PE_SIGNATURE:
> > + return !!(public_key->eku & EKU_codeSigning);
> > + default:
> > + break;
> > + }
> > + return true;
> > +}
> > +#else
> > +static bool check_codesign_eku(struct key *key,
> > + enum key_being_used_for usage)
> > +{
> > + return true;
> > +}
> > +#endif
> > +
> > /*
> > * Check the trust on one PKCS#7 SignedInfo block.
> > */
> > static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > struct pkcs7_signed_info *sinfo,
> > - struct key *trust_keyring)
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage)
> > {
> > struct public_key_signature *sig = sinfo->sig;
> > struct x509_certificate *x509, *last = NULL, *p;
> > @@ -112,6 +136,12 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > return -ENOKEY;
> >
> > matched:
> > + if (!check_codesign_eku(key, usage)) {
>
> Perhaps this can be a generic check_eku_usage() call, with codesigning as one of the
> things it can check for.
>
Because only codesign EKU be checked now. So I prefer to keep it
as my current implementation until there have other EKU requirement.
> > + pr_warn("sinfo %u: The signer %x key is not CodeSigning\n",
> > + sinfo->index, key_serial(key));
> > + key_put(key);
> > + return -ENOKEY;
> > + }
> > ret = verify_signature(key, sig);
> > key_put(key);
> > if (ret < 0) {
> > @@ -156,7 +186,8 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > * May also return -ENOMEM.
> > */
> > int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > - struct key *trust_keyring)
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage)
>
> Please also update the comment above to mention the `usage` parameter.
>
> Regards,
> Varad
I will update it to the comment. Thanks!
Joey Lee
>
> > {
> > struct pkcs7_signed_info *sinfo;
> > struct x509_certificate *p;
> > @@ -167,7 +198,7 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > p->seen = false;
> >
> > for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
> > - ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
> > + ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring, usage);
> > switch (ret) {
> > case -ENOKEY:
> > continue;
> > diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
> > index 38ec7f5f9041..b3b48240ba73 100644
> > --- a/include/crypto/pkcs7.h
> > +++ b/include/crypto/pkcs7.h
> > @@ -30,7 +30,8 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
> > * pkcs7_trust.c
> > */
> > extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > - struct key *trust_keyring);
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage);
> >
> > /*
> > * pkcs7_verify.c
> >
>
> --
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