| Message ID | 20170927221653.11219-2-mjg59@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, 2017-09-27 at 15:16 -0700, Matthew Garrett wrote: > A reasonable configuration is to use IMA to appraise a subset of files > (based on user, security label or other features supported by IMA) but > to also want to use EVM to validate not only the state of the IMA hash > but also additional metadata on the file. Right now this is only > possible if a symmetric key has been loaded, which may not be desirable > in all cases (eg, one where EVM digital signatures are shipped to end > systems rather than EVM HMACs being generated locally). Commit 26ddabfe96bb "evm: enable EVM when X509 certificate is loaded" already allows EVM to be enabled without loading a symmetric key. Mimi > Add an > additional "require_evm" keyword to the IMA policy language in order to > permit the local admin to indicate that they wish EVM validation to > occur even if no symmetric key has been loaded. > > Signed-off-by: Matthew Garrett <mjg59@google.com> > --- > Documentation/ABI/testing/ima_policy | 3 ++- > include/linux/evm.h | 6 ++++-- > security/integrity/evm/evm_main.c | 6 ++++-- > security/integrity/ima/ima_appraise.c | 11 ++++++++++- > security/integrity/ima/ima_policy.c | 12 +++++++++++- > security/integrity/integrity.h | 3 ++- > 6 files changed, 33 insertions(+), 8 deletions(-) > > diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy > index 5dc9eed035fb..ea2703c847f6 100644 > --- a/Documentation/ABI/testing/ima_policy > +++ b/Documentation/ABI/testing/ima_policy > @@ -23,7 +23,8 @@ Description: > [euid=] [fowner=]] > lsm: [[subj_user=] [subj_role=] [subj_type=] > [obj_user=] [obj_role=] [obj_type=]] > - option: [[appraise_type=]] [permit_directio] > + option: [[appraise_type=] [permit_directio] > + [require_evm]] > > base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] > [FIRMWARE_CHECK] > diff --git a/include/linux/evm.h b/include/linux/evm.h > index 35ed9a8a403a..7661f3085942 100644 > --- a/include/linux/evm.h > +++ b/include/linux/evm.h > @@ -19,7 +19,8 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry, > const char *xattr_name, > void *xattr_value, > size_t xattr_value_len, > - struct integrity_iint_cache *iint); > + struct integrity_iint_cache *iint, > + bool force); > extern int evm_inode_setattr(struct dentry *dentry, struct iattr *attr); > extern void evm_inode_post_setattr(struct dentry *dentry, int ia_valid); > extern int evm_inode_setxattr(struct dentry *dentry, const char *name, > @@ -54,7 +55,8 @@ static inline enum integrity_status evm_verifyxattr(struct dentry *dentry, > const char *xattr_name, > void *xattr_value, > size_t xattr_value_len, > - struct integrity_iint_cache *iint) > + struct integrity_iint_cache *iint, > + bool force) > { > return INTEGRITY_UNKNOWN; > } > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > index 063d38aef64e..44e4f4fda965 100644 > --- a/security/integrity/evm/evm_main.c > +++ b/security/integrity/evm/evm_main.c > @@ -223,6 +223,7 @@ static int evm_protected_xattr(const char *req_xattr_name) > * @xattr_name: requested xattr > * @xattr_value: requested xattr value > * @xattr_value_len: requested xattr value length > + * @force: force verification even if no EVM symmetric key is loaded > * > * Calculate the HMAC for the given dentry and verify it against the stored > * security.evm xattr. For performance, use the xattr value and length > @@ -236,9 +237,10 @@ static int evm_protected_xattr(const char *req_xattr_name) > enum integrity_status evm_verifyxattr(struct dentry *dentry, > const char *xattr_name, > void *xattr_value, size_t xattr_value_len, > - struct integrity_iint_cache *iint) > + struct integrity_iint_cache *iint, > + bool force) > { > - if (!evm_initialized || !evm_protected_xattr(xattr_name)) > + if ((!evm_initialized || !evm_protected_xattr(xattr_name)) && !force) > return INTEGRITY_UNKNOWN; > > if (!iint) { > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c > index edb82e722a0d..9df1148f17cc 100644 > --- a/security/integrity/ima/ima_appraise.c > +++ b/security/integrity/ima/ima_appraise.c > @@ -217,6 +217,7 @@ int ima_appraise_measurement(enum ima_hooks func, > struct inode *inode = d_backing_inode(dentry); > enum integrity_status status = INTEGRITY_UNKNOWN; > int rc = xattr_len, hash_start = 0; > + bool evm_force = false; > > if (!(inode->i_opflags & IOP_XATTR)) > return INTEGRITY_UNKNOWN; > @@ -236,7 +237,15 @@ int ima_appraise_measurement(enum ima_hooks func, > goto out; > } > > - status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint); > + /* > + * Check if policy specifies that we should perform EVM > + * validation even in the absence of an EVM symmetric key > + */ > + if (iint->flags & IMA_EVM_REQUIRED) > + evm_force = true; > + > + status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint, > + evm_force); > if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) { > if ((status == INTEGRITY_NOLABEL) > || (status == INTEGRITY_NOXATTRS)) > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c > index a6e14c532627..db4a0c968e00 100644 > --- a/security/integrity/ima/ima_policy.c > +++ b/security/integrity/ima/ima_policy.c > @@ -531,7 +531,7 @@ enum { > Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt, > Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt, > Opt_appraise_type, Opt_permit_directio, > - Opt_pcr > + Opt_pcr, Opt_require_evm, > }; > > static match_table_t policy_tokens = { > @@ -562,6 +562,7 @@ static match_table_t policy_tokens = { > {Opt_appraise_type, "appraise_type=%s"}, > {Opt_permit_directio, "permit_directio"}, > {Opt_pcr, "pcr=%s"}, > + {Opt_require_evm, "require_evm"}, > {Opt_err, NULL} > }; > > @@ -876,6 +877,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) > else > entry->flags |= IMA_PCR; > > + break; > + case Opt_require_evm: > + if (entry->action != APPRAISE) { > + result = -EINVAL; > + break; > + } > + entry->flags |= IMA_EVM_REQUIRED; > break; > case Opt_err: > ima_log_string(ab, "UNKNOWN", p); > @@ -1142,6 +1150,8 @@ int ima_policy_show(struct seq_file *m, void *v) > } > } > } > + if (entry->flags & IMA_EVM_REQUIRED) > + seq_puts(m, "require_evm "); > if (entry->flags & IMA_DIGSIG_REQUIRED) > seq_puts(m, "appraise_type=imasig "); > if (entry->flags & IMA_PERMIT_DIRECTIO) > diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h > index 45ba0e4501d6..2fa0d7bc55fb 100644 > --- a/security/integrity/integrity.h > +++ b/security/integrity/integrity.h > @@ -28,11 +28,12 @@ > > /* iint cache flags */ > #define IMA_ACTION_FLAGS 0xff000000 > -#define IMA_ACTION_RULE_FLAGS 0x06000000 > +#define IMA_ACTION_RULE_FLAGS 0x16000000 > #define IMA_DIGSIG 0x01000000 > #define IMA_DIGSIG_REQUIRED 0x02000000 > #define IMA_PERMIT_DIRECTIO 0x04000000 > #define IMA_NEW_FILE 0x08000000 > +#define IMA_EVM_REQUIRED 0x10000000 > > #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \ > IMA_APPRAISE_SUBMASK)
On Sat, Sep 30, 2017 at 7:08 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > On Wed, 2017-09-27 at 15:16 -0700, Matthew Garrett wrote: >> A reasonable configuration is to use IMA to appraise a subset of files >> (based on user, security label or other features supported by IMA) but >> to also want to use EVM to validate not only the state of the IMA hash >> but also additional metadata on the file. Right now this is only >> possible if a symmetric key has been loaded, which may not be desirable >> in all cases (eg, one where EVM digital signatures are shipped to end >> systems rather than EVM HMACs being generated locally). > > Commit 26ddabfe96bb "evm: enable EVM when X509 certificate is loaded" > already allows EVM to be enabled without loading a symmetric key. This only seems to be set if CONFIG_EVM_LOAD_X509 is set. Should there be some sort of callback to set this if a key is loaded onto the evm keyring at runtime?
On Mon, 2017-10-02 at 10:02 -0700, Matthew Garrett wrote: > On Sat, Sep 30, 2017 at 7:08 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > > On Wed, 2017-09-27 at 15:16 -0700, Matthew Garrett wrote: > >> A reasonable configuration is to use IMA to appraise a subset of files > >> (based on user, security label or other features supported by IMA) but > >> to also want to use EVM to validate not only the state of the IMA hash > >> but also additional metadata on the file. Right now this is only > >> possible if a symmetric key has been loaded, which may not be desirable > >> in all cases (eg, one where EVM digital signatures are shipped to end > >> systems rather than EVM HMACs being generated locally). > > > > Commit 26ddabfe96bb "evm: enable EVM when X509 certificate is loaded" > > already allows EVM to be enabled without loading a symmetric key. > > This only seems to be set if CONFIG_EVM_LOAD_X509 is set. Should there > be some sort of callback to set this if a key is loaded onto the evm > keyring at runtime? Currently writing 1 to the securityfs file causes the EVM key to be loaded. I would extend the existing evm_write_key(). Writing 2, for example, might skip attempting to load the EVM key. You'll probably want to make sure that a public key has been loaded first. Mimi
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index 5dc9eed035fb..ea2703c847f6 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -23,7 +23,8 @@ Description: [euid=] [fowner=]] lsm: [[subj_user=] [subj_role=] [subj_type=] [obj_user=] [obj_role=] [obj_type=]] - option: [[appraise_type=]] [permit_directio] + option: [[appraise_type=] [permit_directio] + [require_evm]] base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] [FIRMWARE_CHECK] diff --git a/include/linux/evm.h b/include/linux/evm.h index 35ed9a8a403a..7661f3085942 100644 --- a/include/linux/evm.h +++ b/include/linux/evm.h @@ -19,7 +19,8 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry, const char *xattr_name, void *xattr_value, size_t xattr_value_len, - struct integrity_iint_cache *iint); + struct integrity_iint_cache *iint, + bool force); extern int evm_inode_setattr(struct dentry *dentry, struct iattr *attr); extern void evm_inode_post_setattr(struct dentry *dentry, int ia_valid); extern int evm_inode_setxattr(struct dentry *dentry, const char *name, @@ -54,7 +55,8 @@ static inline enum integrity_status evm_verifyxattr(struct dentry *dentry, const char *xattr_name, void *xattr_value, size_t xattr_value_len, - struct integrity_iint_cache *iint) + struct integrity_iint_cache *iint, + bool force) { return INTEGRITY_UNKNOWN; } diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 063d38aef64e..44e4f4fda965 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -223,6 +223,7 @@ static int evm_protected_xattr(const char *req_xattr_name) * @xattr_name: requested xattr * @xattr_value: requested xattr value * @xattr_value_len: requested xattr value length + * @force: force verification even if no EVM symmetric key is loaded * * Calculate the HMAC for the given dentry and verify it against the stored * security.evm xattr. For performance, use the xattr value and length @@ -236,9 +237,10 @@ static int evm_protected_xattr(const char *req_xattr_name) enum integrity_status evm_verifyxattr(struct dentry *dentry, const char *xattr_name, void *xattr_value, size_t xattr_value_len, - struct integrity_iint_cache *iint) + struct integrity_iint_cache *iint, + bool force) { - if (!evm_initialized || !evm_protected_xattr(xattr_name)) + if ((!evm_initialized || !evm_protected_xattr(xattr_name)) && !force) return INTEGRITY_UNKNOWN; if (!iint) { diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index edb82e722a0d..9df1148f17cc 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -217,6 +217,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct inode *inode = d_backing_inode(dentry); enum integrity_status status = INTEGRITY_UNKNOWN; int rc = xattr_len, hash_start = 0; + bool evm_force = false; if (!(inode->i_opflags & IOP_XATTR)) return INTEGRITY_UNKNOWN; @@ -236,7 +237,15 @@ int ima_appraise_measurement(enum ima_hooks func, goto out; } - status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint); + /* + * Check if policy specifies that we should perform EVM + * validation even in the absence of an EVM symmetric key + */ + if (iint->flags & IMA_EVM_REQUIRED) + evm_force = true; + + status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint, + evm_force); if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) { if ((status == INTEGRITY_NOLABEL) || (status == INTEGRITY_NOXATTRS)) diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index a6e14c532627..db4a0c968e00 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -531,7 +531,7 @@ enum { Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt, Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt, Opt_appraise_type, Opt_permit_directio, - Opt_pcr + Opt_pcr, Opt_require_evm, }; static match_table_t policy_tokens = { @@ -562,6 +562,7 @@ static match_table_t policy_tokens = { {Opt_appraise_type, "appraise_type=%s"}, {Opt_permit_directio, "permit_directio"}, {Opt_pcr, "pcr=%s"}, + {Opt_require_evm, "require_evm"}, {Opt_err, NULL} }; @@ -876,6 +877,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) else entry->flags |= IMA_PCR; + break; + case Opt_require_evm: + if (entry->action != APPRAISE) { + result = -EINVAL; + break; + } + entry->flags |= IMA_EVM_REQUIRED; break; case Opt_err: ima_log_string(ab, "UNKNOWN", p); @@ -1142,6 +1150,8 @@ int ima_policy_show(struct seq_file *m, void *v) } } } + if (entry->flags & IMA_EVM_REQUIRED) + seq_puts(m, "require_evm "); if (entry->flags & IMA_DIGSIG_REQUIRED) seq_puts(m, "appraise_type=imasig "); if (entry->flags & IMA_PERMIT_DIRECTIO) diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index 45ba0e4501d6..2fa0d7bc55fb 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -28,11 +28,12 @@ /* iint cache flags */ #define IMA_ACTION_FLAGS 0xff000000 -#define IMA_ACTION_RULE_FLAGS 0x06000000 +#define IMA_ACTION_RULE_FLAGS 0x16000000 #define IMA_DIGSIG 0x01000000 #define IMA_DIGSIG_REQUIRED 0x02000000 #define IMA_PERMIT_DIRECTIO 0x04000000 #define IMA_NEW_FILE 0x08000000 +#define IMA_EVM_REQUIRED 0x10000000 #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \ IMA_APPRAISE_SUBMASK)
A reasonable configuration is to use IMA to appraise a subset of files (based on user, security label or other features supported by IMA) but to also want to use EVM to validate not only the state of the IMA hash but also additional metadata on the file. Right now this is only possible if a symmetric key has been loaded, which may not be desirable in all cases (eg, one where EVM digital signatures are shipped to end systems rather than EVM HMACs being generated locally). Add an additional "require_evm" keyword to the IMA policy language in order to permit the local admin to indicate that they wish EVM validation to occur even if no symmetric key has been loaded. Signed-off-by: Matthew Garrett <mjg59@google.com> --- Documentation/ABI/testing/ima_policy | 3 ++- include/linux/evm.h | 6 ++++-- security/integrity/evm/evm_main.c | 6 ++++-- security/integrity/ima/ima_appraise.c | 11 ++++++++++- security/integrity/ima/ima_policy.c | 12 +++++++++++- security/integrity/integrity.h | 3 ++- 6 files changed, 33 insertions(+), 8 deletions(-)