On Wed, 2020-10-14 at 13:00 +0200, Ard Biesheuvel wrote:
> Hello Chester,
>
> Thanks for looking into this.
>
> Some comments below.
>
> On Wed, 14 Oct 2020 at 12:41, Chester Lin <clin@xxxxxxxx> wrote:
> >
> > Separate the get_sb_mode() from arch/x86 and treat it as a common function
> > [rename to efi_get_secureboot_mode] so all EFI-based architectures can
> > reuse the same logic.
> >
> > Signed-off-by: Chester Lin <clin@xxxxxxxx>
> > ---
> > arch/x86/kernel/ima_arch.c | 47 ++------------------------------------
> > drivers/firmware/efi/efi.c | 43 ++++++++++++++++++++++++++++++++++
> > include/linux/efi.h | 5 ++++
> > 3 files changed, 50 insertions(+), 45 deletions(-)
> >
> > diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
> > index 7dfb1e808928..ed4623ecda6e 100644
> > --- a/arch/x86/kernel/ima_arch.c
> > +++ b/arch/x86/kernel/ima_arch.c
> > @@ -8,49 +8,6 @@
> >
> > extern struct boot_params boot_params;
> >
> > -static enum efi_secureboot_mode get_sb_mode(void)
> > -{
> > - efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
> > - efi_status_t status;
> > - unsigned long size;
> > - u8 secboot, setupmode;
> > -
> > - size = sizeof(secboot);
> > -
> > - if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
> > - pr_info("ima: secureboot mode unknown, no efi\n");
> > - return efi_secureboot_mode_unknown;
> > - }
> > -
> > - /* Get variable contents into buffer */
> > - status = efi.get_variable(L"SecureBoot", &efi_variable_guid,
> > - NULL, &size, &secboot);
> > - if (status == EFI_NOT_FOUND) {
> > - pr_info("ima: secureboot mode disabled\n");
> > - return efi_secureboot_mode_disabled;
> > - }
> > -
> > - if (status != EFI_SUCCESS) {
> > - pr_info("ima: secureboot mode unknown\n");
> > - return efi_secureboot_mode_unknown;
> > - }
> > -
> > - size = sizeof(setupmode);
> > - status = efi.get_variable(L"SetupMode", &efi_variable_guid,
> > - NULL, &size, &setupmode);
> > -
> > - if (status != EFI_SUCCESS) /* ignore unknown SetupMode */
> > - setupmode = 0;
> > -
> > - if (secboot == 0 || setupmode == 1) {
> > - pr_info("ima: secureboot mode disabled\n");
> > - return efi_secureboot_mode_disabled;
> > - }
> > -
> > - pr_info("ima: secureboot mode enabled\n");
> > - return efi_secureboot_mode_enabled;
> > -}
> > -
> > bool arch_ima_get_secureboot(void)
> > {
> > static enum efi_secureboot_mode sb_mode;
> > @@ -60,7 +17,7 @@ bool arch_ima_get_secureboot(void)
> > sb_mode = boot_params.secure_boot;
> >
> > if (sb_mode == efi_secureboot_mode_unset)
> > - sb_mode = get_sb_mode();
> > + sb_mode = efi_get_secureboot_mode();
> > initialized = true;
> > }
> >
> > @@ -70,7 +27,7 @@ bool arch_ima_get_secureboot(void)
> > return false;
> > }
> >
> > -/* secureboot arch rules */
> > +/* secure and trusted boot arch rules */
> > static const char * const sb_arch_rules[] = {
> > #if !IS_ENABLED(CONFIG_KEXEC_SIG)
> > "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
> > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > index 5e5480a0a32d..68ffa6a069c0 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -1022,3 +1022,46 @@ static int __init register_update_efi_random_seed(void)
> > }
> > late_initcall(register_update_efi_random_seed);
> > #endif
> > +
> > +enum efi_secureboot_mode efi_get_secureboot_mode(void)
> > +{
> > + efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
> > + efi_status_t status;
> > + unsigned long size;
> > + u8 secboot, setupmode;
> > +
> > + size = sizeof(secboot);
> > +
> > + if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
> > + pr_info("ima: secureboot mode unknown, no efi\n");
>
> These prints don't belong here anymore.
>
> Also, it would be useful if we could reuse this logic in the EFI stub
> as well, which is built as a separate executable, and does not provide
> efi.get_variable().
>
> So, you could you please break this up into
>
> static inline
> enum efi_secureboot_mode efi_get_secureboot_mode(efi_get_variable_t *get_var)
> {
> }
>
> placed into include/linux/efi.h, which encapsulates the core logic,
> but using get_var(), and without the prints.
>
> Then, we could put something like
>
> bool efi_ima_get_secureboot(void)
> {
> }
>
> in drivers/firmware/efi/efi.c (guarded by #ifdef CONFIG_IMA_xxx),
> which performs the
> efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) check, calls
> efi_get_secureboot_mode(efi.get_variable), and implements the logic.
>
> And actually, if the logic is identical between x86 and arm64, I
> wonder if it wouldn't be better to put the whole thing into
>
> drivers/firmware/efi/efi-ima.c
>
> or
>
> security/integrity/ima/ima-efi.c
>
> with the only difference being the boot_params->secure_boot access for
> x86, which we can factor out to a static inline helper.
>
> Mimi, any thoughts here?
Sounds good. Keeping as much IMA code in the IMA directory makes
sense. The IMA Makefile would then include ima-efi.c based on an EFI
Kconfig option.
thanks,
Mimi
>
>
>
> > + return efi_secureboot_mode_unknown;
> > + }
> > +
> > + /* Get variable contents into buffer */
> > + status = efi.get_variable(L"SecureBoot", &efi_variable_guid,
> > + NULL, &size, &secboot);
> > + if (status == EFI_NOT_FOUND) {
> > + pr_info("ima: secureboot mode disabled\n");
> > + return efi_secureboot_mode_disabled;
> > + }
> > +
> > + if (status != EFI_SUCCESS) {
> > + pr_info("ima: secureboot mode unknown\n");
> > + return efi_secureboot_mode_unknown;
> > + }
> > +
> > + size = sizeof(setupmode);
> > + status = efi.get_variable(L"SetupMode", &efi_variable_guid,
> > + NULL, &size, &setupmode);
> > +
> > + if (status != EFI_SUCCESS) /* ignore unknown SetupMode */
> > + setupmode = 0;
> > +
> > + if (secboot == 0 || setupmode == 1) {
> > + pr_info("ima: secureboot mode disabled\n");
> > + return efi_secureboot_mode_disabled;
> > + }
> > +
> > + pr_info("ima: secureboot mode enabled\n");
> > + return efi_secureboot_mode_enabled;
> > +}
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index d7c0e73af2b9..a73e5ae04672 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -1076,8 +1076,13 @@ static inline int efi_runtime_map_copy(void *buf, size_t bufsz)
> >
> > #ifdef CONFIG_EFI
> > extern bool efi_runtime_disabled(void);
> > +extern enum efi_secureboot_mode efi_get_secureboot_mode(void);
> > #else
> > static inline bool efi_runtime_disabled(void) { return true; }
> > +static inline enum efi_secureboot_mode efi_get_secureboot_mode(void)
> > +{
> > + return efi_secureboot_mode_disabled;
> > +}
> > #endif
> >
> > extern void efi_call_virt_check_flags(unsigned long flags, const char *call);
> > --
> > 2.26.1
> >
