On Fri, May 03, 2019 at 04:23:51PM +0200, Ard Biesheuvel wrote: > On Fri, 3 May 2019 at 10:59, joeyli <jlee@xxxxxxxx> wrote: > > > > On Fri, May 03, 2019 at 10:07:59AM +0200, Ard Biesheuvel wrote: > > > On Fri, 3 May 2019 at 09:18, joeyli <jlee@xxxxxxxx> wrote: > > > > > > > > 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 <joeyli.kernel@xxxxxxxxx> wrote: > > > > > > > > > > > > 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@xxxxxxxxx> > > > > > > Cc: Serge E. Hallyn" <serge@xxxxxxxxxx> > > > > > > Cc: David Howells <dhowells@xxxxxxxxxx> > > > > > > Cc: Nayna Jain <nayna@xxxxxxxxxxxxx> > > > > > > Cc: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> > > > > > > Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx> > > > > > > Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx> > > > > > > --- > > > > > > 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. > > > > > > > > > > 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. > > > > > > > > > > I understand that. But I don't think we need it. > > > > > > > OK. I will remove the debug message. > > > > > > > > } > > > > > > + 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! > > > > > > > > > > @@ -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. > > > > > > > > > > Yes, but if secure boot is enabled and db is empty, how could you have > > > booted in the first place? > > > > > > > I agree. When secure boot enabled, kernel can not be booted without db. > > > > > And what about the converse case: if secure boot is not enabled, why > > > should we trust the contents of db? > > > > > > > The db and dbx are authenticated variables that it protected by KEK. > > So it can be trusted even secure boot is disabled. Unless manufacturer > > or user's KEK is leaked. > > > > Is that true for non-secureboot capable firmware? Of course, in that > case, we cannot be sure that the kernel itself is trusted, but we > shouldn't open up another hole either. > I agree with you that we should filer-out non-secureboot firmware. I think that we can check the existence of SecureBoot variable before loading db/dbx. On the other hand, the SetupMode should also be checked because db/dbx can be changed in setup mode. > > > > > - secure boot might be enabled but we may be booting without shim. > > > > > > > > Shim always creates MokListRT no matter secure boot enabled or disabled. > > > > > > > > > > That is not my point. What happens if you booted with secure boot > > > enabled but without the help of shim? > > > > > > > Without shim, the signed EFI stub can still be booted by EFI boot manager. > > But the MokListRT will not be created for runtime. So MOK signed kernel > > module can not be verified. (or IMA can not verify MOK signed kernel image > > for kexec...) > > > > So if we opt out of using shim, we lose kexec capability as well? That > doesn't make any sense. > MOK is just one of options that it can be used to sign crash kernel image. We can also use the key in db or the kernel embedded keys. > In general, I am very uncomfortable with the way we have painted > ourselves into a corner with shim. If I install Suse on a system that > has the Suse cert in db or KEK, why would I need shim in the first > place? > Yes! We don't need MOK if distro's certificates are preloaded in most machines' db. Unfortunately it's not the case on most x86 machines. > > > > > - 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. > > > > > > > > > > Yes, but again, depending on whether shim was involved, and/or whether > > > secure boot was enabled or not, the way we interpret these things may > > > be very different. > > > > > > I want the reasoning to be sound before merging any patches that deal > > > with these variables. > > > > Here is a simple summary: > > > > When secure boot is enabled: > > - db/dbx: Can be trusted because they are authenticated variables. > > (unless end user doesn't want to trust db/dbx) > > - MokListRT: > > - with shim: MokListRT will be created. It can be trusted. > > - without shim: MokListRT will not be created. > > MOK protected kernel module or file can not be > > verified. > > > > So who polices that MoKlistRT is not created? > At boot time, shim copies MokList (boot variable) to MokListRT (runtime variable). The MokListRT is a read-only runtime volatile variable. So, without shim, the MokListRT will not be created for runtime. > > When secure boot is disabled: > > - db/dbx: Can be trusted because they are authenticated variables. > > (unless end user doesn't want to trust db/dbx) > > Is this true? Does non-secure boot capable firmware still guarantee > that db/dbx can't be created? > I agree. So we should check the existence of SecureBoot variable as I mentioned above. > > - MokListRT: > > - with shim: MokListRT will be created. But it can not be trusted. > > MOK protected kernel module or file can not be > > verified. > > - without shim: MokListRT will not be created. > > MOK protected kernel module or file can not be > > verified. > > > > Enabling this securely involves more than connecting the dots when it > comes to db, MokListRT etc. I would like for someone to convince me as > a maintainer, as well as the IMA maintainers, that the security > requirements are still met in all cases we care about. Just copying db > and MokListRT into a kernel keychain doesn't appear to do that, and if > it does, it needs more documentation to clarify that. Welcome for more input from other maintainers. But I hope that my cosmetic can be accepted because current warning messages looks ugly. Thanks a lot! Joey Lee
