Re: [PATCH 2/2] efi: show error messages only when loading certificates is failed

[Joey Lee]

Hi Ard,

On Fri, Dec 13, 2019 at 09:10:12AM +0000, Ard Biesheuvel wrote:
> On Fri, 13 Dec 2019 at 10:07, Lee, Chun-Yi <joeyli.kernel@xxxxxxxxx> wrote:
> >
> > When loading certificates list from EFI variables, the error
> > message and efi status code always be emitted to dmesg. 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
> >
> > This cosmetic patch moved the messages to the error handling code
> > path. And, it also shows the corresponding status string of status
> > code.
> >
> 
> So what output do we get after applying this patch when those
> variables don't exist?
>

A "UEFI:xxxx list was not found" message will be exposed in dmesg
when kernel loglevel be set to debug. Otherwise there have no messages.

Thanks
Joey Lee
 
> > Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx>
> > ---
> >  security/integrity/platform_certs/load_uefi.c | 40 ++++++++++++++-------------
> >  1 file changed, 21 insertions(+), 19 deletions(-)
> >
> > diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
> > index 81b19c52832b..b6c60fb3fb6c 100644
> > --- a/security/integrity/platform_certs/load_uefi.c
> > +++ b/security/integrity/platform_certs/load_uefi.c
> > @@ -1,4 +1,5 @@
> >  // SPDX-License-Identifier: GPL-2.0
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> >
> >  #include <linux/kernel.h>
> >  #include <linux/sched.h>
> > @@ -39,7 +40,7 @@ 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, const char *source)
> >  {
> >         efi_status_t status;
> >         unsigned long lsize = 4;
> > @@ -48,23 +49,30 @@ static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
> >
> >         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);
> > -               return NULL;
> > +               if (status == EFI_NOT_FOUND) {
> > +                       pr_debug("%s list was not found\n", source);
> > +                       return NULL;
> > +               }
> > +               goto err;
> >         }
> >
> >         db = kmalloc(lsize, GFP_KERNEL);
> > -       if (!db)
> > -               return NULL;
> > +       if (!db) {
> > +               status = EFI_OUT_OF_RESOURCES;
> > +               goto err;
> > +       }
> >
> >         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);
> > -               return NULL;
> > +               goto err;
> >         }
> >
> >         *size = lsize;
> >         return db;
> > +err:
> > +       pr_err("Couldn't get %s list: %s\n", source, efi_status_to_str(status));
> > +       return NULL;
> >  }
> >
> >  /*
> > @@ -153,10 +161,8 @@ 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);
> > -               if (!db) {
> > -                       pr_err("MODSIGN: Couldn't get UEFI db list\n");
> > -               } else {
> > +               db = get_cert_list(L"db", &secure_var, &dbsize, "UEFI:db");
> > +               if (db) {
> >                         rc = parse_efi_signature_list("UEFI:db",
> >                                         db, dbsize, get_handler_for_db);
> >                         if (rc)
> > @@ -166,10 +172,8 @@ 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 {
> > +       mok = get_cert_list(L"MokListRT", &mok_var, &moksize, "UEFI:MokListRT");
> > +       if (mok) {
> >                 rc = parse_efi_signature_list("UEFI:MokListRT",
> >                                               mok, moksize, get_handler_for_db);
> >                 if (rc)
> > @@ -177,10 +181,8 @@ static int __init load_uefi_certs(void)
> >                 kfree(mok);
> >         }
> >
> > -       dbx = get_cert_list(L"dbx", &secure_var, &dbxsize);
> > -       if (!dbx) {
> > -               pr_info("Couldn't get UEFI dbx list\n");
> > -       } else {
> > +       dbx = get_cert_list(L"dbx", &secure_var, &dbxsize, "UEFI:dbx");
> > +       if (dbx) {
> >                 rc = parse_efi_signature_list("UEFI:dbx",
> >                                               dbx, dbxsize,
> >                                               get_handler_for_dbx);
> > --
> > 2.16.4
> >