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Message-ID: <CAMj1kXGacnj=uh9WFh1+YBVXxzZbxeN==Y_f-rhJZ=3385B68g@mail.gmail.com>
Date: Wed, 14 Oct 2020 13:00:44 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Chester Lin <clin@...e.com>
Cc: Mimi Zohar <zohar@...ux.ibm.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Mark Rutland <mark.rutland@....com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Masahiro Yamada <masahiroy@...nel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
X86 ML <x86@...nel.org>,
linux-integrity <linux-integrity@...r.kernel.org>,
linux-efi <linux-efi@...r.kernel.org>,
"Lee, Chun-Yi" <jlee@...e.com>
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 <clin@...e.com> 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@...e.com>
> ---
> 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
>
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