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Message-ID: <CAKv+Gu-a5Bo9i=K55pa3jEXRq-u5JYVGp1jFEE=UY5B=6eUkRQ@mail.gmail.com>
Date: Mon, 17 Feb 2020 14:37:54 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Javier Martinez Canillas <javierm@...hat.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-efi <linux-efi@...r.kernel.org>,
Hans de Goede <hdegoede@...hat.com>,
Eric Richter <erichte@...ux.ibm.com>,
James Morris <jmorris@...ei.org>,
Michael Ellerman <mpe@...erman.id.au>,
Mimi Zohar <zohar@...ux.ibm.com>,
Nayna Jain <nayna@...ux.ibm.com>,
"Serge E. Hallyn" <serge@...lyn.com>,
YueHaibing <yuehaibing@...wei.com>,
linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [RESEND PATCH v2] efi: Only print errors about failing to get
certs if EFI vars are found
On Mon, 17 Feb 2020 at 12:40, Javier Martinez Canillas
<javierm@...hat.com> wrote:
>
> If CONFIG_LOAD_UEFI_KEYS is enabled, the kernel attempts to load the certs
> from the db, dbx and MokListRT EFI variables into the appropriate keyrings.
>
> But it just assumes that the variables will be present and prints an error
> if the certs can't be loaded, even when is possible that the variables may
> not exist. For example the MokListRT variable will only be present if shim
> is used.
>
> So only print an error message about failing to get the certs list from an
> EFI variable if this is found. Otherwise these printed errors just pollute
> the kernel log ring buffer with confusing messages like the following:
>
> [ 5.427251] Couldn't get size: 0x800000000000000e
> [ 5.427261] MODSIGN: Couldn't get UEFI db list
> [ 5.428012] Couldn't get size: 0x800000000000000e
> [ 5.428023] Couldn't get UEFI MokListRT
>
> Reported-by: Hans de Goede <hdegoede@...hat.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> Tested-by: Hans de Goede <hdegoede@...hat.com>
Acked-by: Ard Biesheuvel <ardb@...nel.org>
>
> ---
>
> Changes in v2:
> - Fix flaws in the logic, that caused the signature list was parsed if
> the return code was EFI_NOT_FOUND that pointed out Hans de Goede.
> - Print debug messages if the variables are not found.
>
> security/integrity/platform_certs/load_uefi.c | 40 ++++++++++++-------
> 1 file changed, 26 insertions(+), 14 deletions(-)
>
> diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
> index 111898aad56..f0c90824196 100644
> --- a/security/integrity/platform_certs/load_uefi.c
> +++ b/security/integrity/platform_certs/load_uefi.c
> @@ -35,16 +35,18 @@ static __init bool uefi_check_ignore_db(void)
> * Get a certificate list blob from the named EFI variable.
> */
> static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
> - unsigned long *size)
> + unsigned long *size, efi_status_t *status)
> {
> - efi_status_t status;
> unsigned long lsize = 4;
> unsigned long tmpdb[4];
> void *db;
>
> - 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);
> + *status = efi.get_variable(name, guid, NULL, &lsize, &tmpdb);
> + if (*status == EFI_NOT_FOUND)
> + return NULL;
> +
> + if (*status != EFI_BUFFER_TOO_SMALL) {
> + pr_err("Couldn't get size: 0x%lx\n", *status);
> return NULL;
> }
>
> @@ -52,10 +54,10 @@ static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
> if (!db)
> return NULL;
>
> - status = efi.get_variable(name, guid, NULL, &lsize, db);
> - if (status != EFI_SUCCESS) {
> + *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 db var: 0x%lx\n", *status);
> return NULL;
> }
>
> @@ -74,6 +76,7 @@ static int __init load_uefi_certs(void)
> efi_guid_t mok_var = EFI_SHIM_LOCK_GUID;
> void *db = NULL, *dbx = NULL, *mok = NULL;
> unsigned long dbsize = 0, dbxsize = 0, moksize = 0;
> + efi_status_t status;
> int rc = 0;
>
> if (!efi.get_variable)
> @@ -83,9 +86,12 @@ static int __init load_uefi_certs(void)
> * an error if we can't get them.
> */
> if (!uefi_check_ignore_db()) {
> - db = get_cert_list(L"db", &secure_var, &dbsize);
> + db = get_cert_list(L"db", &secure_var, &dbsize, &status);
> if (!db) {
> - pr_err("MODSIGN: Couldn't get UEFI db list\n");
> + if (status == EFI_NOT_FOUND)
> + pr_debug("MODSIGN: db variable wasn't found\n");
> + else
> + pr_err("MODSIGN: Couldn't get UEFI db list\n");
> } else {
> rc = parse_efi_signature_list("UEFI:db",
> db, dbsize, get_handler_for_db);
> @@ -96,9 +102,12 @@ static int __init load_uefi_certs(void)
> }
> }
>
> - mok = get_cert_list(L"MokListRT", &mok_var, &moksize);
> + mok = get_cert_list(L"MokListRT", &mok_var, &moksize, &status);
> if (!mok) {
> - pr_info("Couldn't get UEFI MokListRT\n");
> + if (status == EFI_NOT_FOUND)
> + pr_debug("MokListRT variable wasn't found\n");
> + else
> + pr_info("Couldn't get UEFI MokListRT\n");
> } else {
> rc = parse_efi_signature_list("UEFI:MokListRT",
> mok, moksize, get_handler_for_db);
> @@ -107,9 +116,12 @@ static int __init load_uefi_certs(void)
> kfree(mok);
> }
>
> - dbx = get_cert_list(L"dbx", &secure_var, &dbxsize);
> + dbx = get_cert_list(L"dbx", &secure_var, &dbxsize, &status);
> if (!dbx) {
> - pr_info("Couldn't get UEFI dbx list\n");
> + if (status == EFI_NOT_FOUND)
> + pr_debug("dbx variable wasn't found\n");
> + else
> + pr_info("Couldn't get UEFI dbx list\n");
> } else {
> rc = parse_efi_signature_list("UEFI:dbx",
> dbx, dbxsize,
> --
> 2.24.1
>
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