Hi Ard,

On Thu, May 02, 2019 at 11:04:34AM +0200, Ard Biesheuvel wrote:

On Thu, 2 May 2019 at 06:04, Lee, Chun-Yi [off-list ref] wrote:

quoted

When loading certificates list from UEFI variable, the original error
message direct shows the efi status code from UEFI firmware. It looks
ugly:

[    2.335031] Couldn't get size: 0x800000000000000e
[    2.335032] Couldn't get UEFI MokListRT
[    2.339985] Couldn't get size: 0x800000000000000e
[    2.339987] Couldn't get UEFI dbx list

So, this patch shows the status string instead of status code.

On the other hand, the "Couldn't get UEFI" message doesn't need
to be exposed when db/dbx/mok variable do not exist. So, this
patch set the message level to debug.

v3.
- Print messages similar to db/mok when loading dbx hash to blacklist:
[    1.500952] EFI: Blacklisting hash of an executable: UEFI:dbx
[    1.501773] blacklist: Loaded blacklisting hash
'bin:80b4d96931bf0d02fd91a61e19d14f1da452e66db2408ca8604d411f92659f0a'

- Setting messages for the existence of db/mok/dbx lists to debug level.

v2.
Setting the MODSIGN messages level to debug.

Link:
https://forums.opensuse.org/showthread.php/535324-MODSIGN-Couldn-t-get-UEFI-db-list?p=2897516#post2897516
Cc: James Morris <jmorris@namei.org>
Cc: Serge E. Hallyn" <serge@hallyn.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Nayna Jain <nayna@linux.ibm.com>
Cc: Josh Boyer <redacted>
Cc: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 certs/blacklist.c                             |  3 +-
 security/integrity/platform_certs/load_uefi.c | 40 +++++++++++++++++++--------
 2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/certs/blacklist.c b/certs/blacklist.c
index 3a507b9e2568..f91437e39e44 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c

@@ -100,7 +100,8 @@ int mark_hash_blacklisted(const char *hash)
        if (IS_ERR(key)) {
                pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
                return PTR_ERR(key);
-       }
+       } else
+               pr_notice("Loaded blacklisting hash '%s'\n", hash);
        return 0;
 }

diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
index 81b19c52832b..6b6996e5bc27 100644
--- a/security/integrity/platform_certs/load_uefi.c
+++ b/security/integrity/platform_certs/load_uefi.c

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0

+#define pr_fmt(fmt) "EFI: "fmt
+
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/cred.h>

@@ -35,6 +37,18 @@ static __init bool uefi_check_ignore_db(void)
        return status == EFI_SUCCESS;
 }

+static void str16_to_str(efi_char16_t *str16, char *str, int str_size)
+{
+       int i = 0;
+
+       while (str16[i] != '\0' && i < (str_size - 1)) {
+               str[i] = str16[i];
+               i++;
+       }
+
+       str[i] = '\0';
+}
+
 /*
  * Get a certificate list blob from the named EFI variable.
  */

@@ -44,13 +58,20 @@ static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
        efi_status_t status;
        unsigned long lsize = 4;
        unsigned long tmpdb[4];
+       char namestr[16];
        void *db;

+       str16_to_str(name, namestr, ARRAY_SIZE(namestr));

Please drop this (and the function above) - instead, just return NULL
if the variable is not found (without reporting an error).

This name string is for printing debug level message, not error message.
This function already returns NULL when EFI_NOT_FOUND be returned by
firmware.
 

quoted

        status = efi.get_variable(name, guid, NULL, &lsize, &tmpdb);
        if (status != EFI_BUFFER_TOO_SMALL) {
-               pr_err("Couldn't get size: 0x%lx\n", status);
+               if (status == EFI_NOT_FOUND)
+                       pr_debug("UEFI %s list doesn't exist\n", namestr);
+               else
+                       pr_err("Couldn't get size for UEFI %s list: %s\n",
+                               namestr, efi_status_to_str(status));
                return NULL;

here returns NULL when EFI_NOT_FOUND. The message of existence is for
debugging. 

quoted

        }
+       pr_debug("UEFI %s list exists\n", namestr);

        db = kmalloc(lsize, GFP_KERNEL);
        if (!db)

@@ -59,7 +80,8 @@ static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
        status = efi.get_variable(name, guid, NULL, &lsize, db);
        if (status != EFI_SUCCESS) {
                kfree(db);
-               pr_err("Error reading db var: 0x%lx\n", status);
+               pr_err("Error reading UEFI %s list: %s\n",
+                       namestr, efi_status_to_str(status));
                return NULL;
        }

@@ -95,6 +117,7 @@ static __init void uefi_blacklist_hash(const char *source, const void *data,
 static __init void uefi_blacklist_x509_tbs(const char *source,
                                           const void *data, size_t len)
 {
+       pr_info("Blacklisting X.509 TBS hash: %s\n", source);
        uefi_blacklist_hash(source, data, len, "tbs:", 4);
 }

@@ -104,6 +127,7 @@ static __init void uefi_blacklist_x509_tbs(const char *source,
 static __init void uefi_blacklist_binary(const char *source,
                                         const void *data, size_t len)
 {
+       pr_info("Blacklisting hash of an executable: %s\n", source);
        uefi_blacklist_hash(source, data, len, "bin:", 4);
 }

These are separate changes - I don't have an opinion whether they are
appropriate or not, but they should be in a separate patch.

I will move the message of blacklising hash to other patch. Thanks!
 

quoted

@@ -154,9 +178,7 @@ static int __init load_uefi_certs(void)
         */
        if (!uefi_check_ignore_db()) {
                db = get_cert_list(L"db", &secure_var, &dbsize);
-               if (!db) {
-                       pr_err("MODSIGN: Couldn't get UEFI db list\n");
-               } else {
+               if (db) {
                        rc = parse_efi_signature_list("UEFI:db",
                                        db, dbsize, get_handler_for_db);
                        if (rc)

@@ -167,9 +189,7 @@ static int __init load_uefi_certs(void)
        }

        mok = get_cert_list(L"MokListRT", &mok_var, &moksize);
-       if (!mok) {
-               pr_info("Couldn't get UEFI MokListRT\n");
-       } else {
+       if (mok) {
                rc = parse_efi_signature_list("UEFI:MokListRT",
                                              mok, moksize, get_handler_for_db);
                if (rc)

@@ -178,9 +198,7 @@ static int __init load_uefi_certs(void)
        }

        dbx = get_cert_list(L"dbx", &secure_var, &dbxsize);
-       if (!dbx) {
-               pr_info("Couldn't get UEFI dbx list\n");
-       } else {
+       if (dbx) {
                rc = parse_efi_signature_list("UEFI:dbx",
                                              dbx, dbxsize,
                                              get_handler_for_dbx);
--

2.16.4

I think we should consider carefully what it means if some of these
variables don't exist:
- if secure boot is enabled, db and dbx must exist, so if they don't,
something is wrong

The existence of db/dbx is not related to secure boot. If manufacturer/user
enrolled certificate/hash to db or dbx, then the variable will be created.
If user didn't enroll anything to db/dbx, then variables will not show up.

- secure boot might be enabled but we may be booting without shim.

Shim always creates MokListRT no matter secure boot enabled or disabled.

- secure boot might be disabled.

It's not about secure boot, db/dbx/MokListRT are always available at
runtime if user was enrolled something to those list.
 

Tweaking the severity of error messages without having a clear idea of
the policy we are aiming to implement is likely to cause trouble down
the road, so perhaps someone could explain what this code does, and
how it should behave in the above circumstances.

Thanks
Joey Lee