2020-10-14 15:54:43

by Chester Lin

Subject: [PATCH v2 1/2] efi: add secure boot get helper

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 <[email protected]>
---
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");
+ 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

2020-10-14 15:58:52

by Chester Lin

Subject: Re: [PATCH v2 1/2] efi: add secure boot get helper

Hi Ard and Mimi,

On Wed, Oct 14, 2020 at 06:40:31PM +0800, Chester Lin 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 <[email protected]>
> ---
> 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

I hope you don't mind that I temporarily move the get_sb_mode() to efi
since I'm not sure which place is better. Please let me know if any
suggestions.

Thanks,
Chester

> @@ -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");
> + 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
>

2020-10-14 15:59:08

by Ard Biesheuvel

Subject: Re: [PATCH v2 1/2] efi: add secure boot get helper

Hello Chester,

Thanks for looking into this.

Some comments below.

On Wed, 14 Oct 2020 at 12:41, Chester Lin <[email protected]> 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 <[email protected]>
> ---
> 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?



> + 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
>

2020-10-14 16:08:16

by Mimi Zohar

Subject: Re: [PATCH v2 1/2] efi: add secure boot get helper

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 <[email protected]> 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 <[email protected]>
> > ---
> > 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
> >

2020-10-15 12:38:11

by Chester Lin

Subject: Re: [PATCH v2 1/2] efi: add secure boot get helper

Hi Ard and Mimi,

On Wed, Oct 14, 2020 at 07:56:17AM -0400, Mimi Zohar wrote:
> 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 <[email protected]> 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 <[email protected]>
> > > ---
> > > 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

Thanks for your suggestions. I will include them in v3.

Regards,
Chester

> >
> >
> >
> > > + 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
> > >
>
>