[PATCH 0/2] EVM: add some debugging info

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Revision v1 of 2 in this series.

4 messages, 2 authors, 2021-06-08 · open the first message on its own page

[PATCH 0/2] EVM: add some debugging info

From: Mimi Zohar <zohar@linux.ibm.com>
Date: 2021-06-08 13:30:11

With the recent EVM portable & immutable signature usability improvements
and the ability of including the EVM portable signatures in the IMA
measurement list, adding some dynamic debugging information - security
xattrs and file metadata (misc info) - would be useful.

Mimi Zohar (2):
  ima: differentiate between EVM failures in the audit log
  evm: output EVM digest calculation info

 security/integrity/evm/evm_crypto.c   | 42 +++++++++++++++++++++++++++
 security/integrity/evm/evm_main.c     |  4 +++
 security/integrity/ima/ima_appraise.c |  3 +-
 3 files changed, 48 insertions(+), 1 deletion(-)

-- 
2.27.0

[PATCH 2/2] evm: output EVM digest calculation info

From: Mimi Zohar <zohar@linux.ibm.com>
Date: 2021-06-08 13:30:17

Output the data used in calculating the EVM digest and the resulting
digest as ascii hexadecimal strings.

Suggested-by: Lakshmi Ramasubramanian <redacted> (CONFIG_DYNAMIC_DEBUG)
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
Changelog:
- Use pr_debug *phN format
- Define dump_security_xattr() for larger binary data
- Based on CONFIG_DYNAMIC_DEBUG

 security/integrity/evm/evm_crypto.c | 42 +++++++++++++++++++++++++++++
 security/integrity/evm/evm_main.c   |  4 +++
 2 files changed, 46 insertions(+)

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 1628e2ca9862..900cf8a157b6 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c

@@ -10,6 +10,8 @@
  *	 Using root's kernel master key (kmk), calculate the HMAC
  */
 
+#define pr_fmt(fmt) "EVM: "fmt
+
 #include <linux/export.h>
 #include <linux/crypto.h>
 #include <linux/xattr.h>

@@ -175,6 +177,29 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 	    type != EVM_XATTR_PORTABLE_DIGSIG)
 		crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
 	crypto_shash_final(desc, digest);
+
+	pr_debug("hmac_misc: (%lu) [%*phN]\n", sizeof(struct h_misc),
+		 (int) sizeof(struct h_misc), &hmac_misc);
+}
+
+/*
+ * Dump large security xattr values as a continuous ascii hexademical string.
+ * (pr_debug is limited to 64 bytes.)
+ */
+static void dump_security_xattr(const char *prefix, const void *src, size_t count)
+{
+#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
+	char *asciihex, *p;
+
+	p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
+	if (!asciihex)
+		return;
+
+	p = bin2hex(p, src, count);
+	*p = 0;
+	pr_debug("%s: (%lu) %.*s\n", prefix, count, (int) count * 2, asciihex);
+	kfree(asciihex);
+#endif
 }
 
 /*

@@ -230,6 +255,16 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 					     req_xattr_value_len);
 			if (is_ima)
 				ima_present = true;
+
+			if (req_xattr_value_len < 64)
+				pr_debug("%s: (%lu) [%*phN]\n", req_xattr_name,
+					 req_xattr_value_len,
+					 (int)req_xattr_value_len,
+					 req_xattr_value);
+			else
+				dump_security_xattr(req_xattr_name,
+						    req_xattr_value,
+						    req_xattr_value_len);
 			continue;
 		}
 		size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr->name,

@@ -246,6 +281,13 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
 		if (is_ima)
 			ima_present = true;
+
+		if (xattr_size < 64)
+			pr_debug("%s: (%lu) [%*phN]", xattr->name, xattr_size,
+				 (int)xattr_size, xattr_value);
+		else
+			dump_security_xattr(xattr->name, xattr_value,
+					    xattr_size);
 	}
 	hmac_add_misc(desc, inode, type, data->digest);

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 2c226e634ae9..059ac17a0041 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -11,6 +11,8 @@
  *	evm_inode_removexattr, and evm_verifyxattr
  */
 
+#define pr_fmt(fmt) "EVM: "fmt
+
 #include <linux/init.h>
 #include <linux/crypto.h>
 #include <linux/audit.h>

@@ -272,6 +274,8 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 		else
 			evm_status = INTEGRITY_FAIL;
 	}
+	pr_debug("digest: (%d) [%*phN]\n", digest.hdr.length, digest.hdr.length,
+		  digest.digest);
 out:
 	if (iint)
 		iint->evm_status = evm_status;

-- 
2.27.0

[PATCH 1/2] ima: differentiate between EVM failures in the audit log

From: Mimi Zohar <zohar@linux.ibm.com>
Date: 2021-06-08 13:30:19

Differentiate between an invalid EVM portable signature failure
from other EVM HMAC/signature failures.

Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_appraise.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 940695e7b535..ef9dcfce45d4 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -422,7 +422,8 @@ int ima_appraise_measurement(enum ima_hooks func,
 		goto out;
 	case INTEGRITY_FAIL_IMMUTABLE:
 		set_bit(IMA_DIGSIG, &iint->atomic_flags);
-		fallthrough;
+		cause = "invalid-fail-immutable";
+		goto out;
 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
 		cause = "invalid-HMAC";
 		goto out;

-- 
2.27.0

Re: [PATCH 2/2] evm: output EVM digest calculation info

From: nramas <hidden>
Date: 2021-06-08 16:06:02

On Tue, 2021-06-08 at 09:29 -0400, Mimi Zohar wrote:

Output the data used in calculating the EVM digest and the resulting
digest as ascii hexadecimal strings.

Reviewed-by: Lakshmi Ramasubramanian <redacted>

quoted hunk

Suggested-by: Lakshmi Ramasubramanian <redacted>
(CONFIG_DYNAMIC_DEBUG)
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
Changelog:
- Use pr_debug *phN format
- Define dump_security_xattr() for larger binary data
- Based on CONFIG_DYNAMIC_DEBUG

 security/integrity/evm/evm_crypto.c | 42
+++++++++++++++++++++++++++++
 security/integrity/evm/evm_main.c   |  4 +++
 2 files changed, 46 insertions(+)

diff --git a/security/integrity/evm/evm_crypto.c

b/security/integrity/evm/evm_crypto.c
index 1628e2ca9862..900cf8a157b6 100644

--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c

@@ -10,6 +10,8 @@
  *	 Using root's kernel master key (kmk), calculate the HMAC
  */
 
+#define pr_fmt(fmt) "EVM: "fmt
+
 #include <linux/export.h>
 #include <linux/crypto.h>
 #include <linux/xattr.h>

@@ -175,6 +177,29 @@ static void hmac_add_misc(struct shash_desc

*desc, struct inode *inode,
 	    type != EVM_XATTR_PORTABLE_DIGSIG)
 		crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid,
UUID_SIZE);
 	crypto_shash_final(desc, digest);
+
+	pr_debug("hmac_misc: (%lu) [%*phN]\n", sizeof(struct h_misc),
+		 (int) sizeof(struct h_misc), &hmac_misc);
+}
+
+/*
+ * Dump large security xattr values as a continuous ascii
hexademical string.
+ * (pr_debug is limited to 64 bytes.)
+ */
+static void dump_security_xattr(const char *prefix, const void *src,
size_t count)
+{
+#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
+	char *asciihex, *p;
+
+	p = asciihex = kmalloc(count * 2 + 1, GFP_KERNEL);
+	if (!asciihex)
+		return;
+
+	p = bin2hex(p, src, count);
+	*p = 0;
+	pr_debug("%s: (%lu) %.*s\n", prefix, count, (int) count * 2,
asciihex);
+	kfree(asciihex);
+#endif
 }
 
 /*

@@ -230,6 +255,16 @@ static int evm_calc_hmac_or_hash(struct dentry

*dentry,
 					     req_xattr_value_len);
 			if (is_ima)
 				ima_present = true;
+
+			if (req_xattr_value_len < 64)
+				pr_debug("%s: (%lu) [%*phN]\n",
req_xattr_name,
+					 req_xattr_value_len,
+					 (int)req_xattr_value_len,
+					 req_xattr_value);
+			else
+				dump_security_xattr(req_xattr_name,
+						    req_xattr_value,
+						    req_xattr_value_len
);
 			continue;
 		}
 		size = vfs_getxattr_alloc(&init_user_ns, dentry, xattr-

quoted

name,

@@ -246,6 +281,13 @@ static int evm_calc_hmac_or_hash(struct dentry

*dentry,
 		crypto_shash_update(desc, (const u8 *)xattr_value,
xattr_size);
 		if (is_ima)
 			ima_present = true;
+
+		if (xattr_size < 64)
+			pr_debug("%s: (%lu) [%*phN]", xattr->name,
xattr_size,
+				 (int)xattr_size, xattr_value);
+		else
+			dump_security_xattr(xattr->name, xattr_value,
+					    xattr_size);
 	}
 	hmac_add_misc(desc, inode, type, data->digest);

diff --git a/security/integrity/evm/evm_main.c

b/security/integrity/evm/evm_main.c
index 2c226e634ae9..059ac17a0041 100644

--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -11,6 +11,8 @@
  *	evm_inode_removexattr, and evm_verifyxattr
  */
 
+#define pr_fmt(fmt) "EVM: "fmt
+
 #include <linux/init.h>
 #include <linux/crypto.h>
 #include <linux/audit.h>

@@ -272,6 +274,8 @@ static enum integrity_status

evm_verify_hmac(struct dentry *dentry,
 		else
 			evm_status = INTEGRITY_FAIL;
 	}
+	pr_debug("digest: (%d) [%*phN]\n", digest.hdr.length,
digest.hdr.length,
+		  digest.digest);
 out:
 	if (iint)
 		iint->evm_status = evm_status;

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