linux-kernel - Re: [PATCH v2 2/3] arch/x86: Add <asm/ima-efi.h> for arch_ima_efi_boot

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Date: Tue, 2 Jan 2024 15:07:10 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 bhelgaas@...gle.com, arnd@...db.de, zohar@...ux.ibm.com,
 dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
 serge@...lyn.com, javierm@...hat.com, linux-arch@...r.kernel.org,
 linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, linux-integrity@...r.kernel.org,
 linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2 2/3] arch/x86: Add <asm/ima-efi.h> for
 arch_ima_efi_boot_mode

Hii Ard

Am 19.12.23 um 12:38 schrieb Ard Biesheuvel:
> Hi Thomas,
> 
> On Fri, 15 Dec 2023 at 13:26, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>>
>> The header file <asm/efi.h> contains the macro arch_ima_efi_boot_mode,
>> which expands to use struct boot_params from <asm/bootparams.h>. Many
>> drivers include <linux/efi.h>, but do not use boot parameters. Changes
>> to bootparam.h or its included headers can easily trigger large,
>> unnessary rebuilds of the kernel.
>>
>> Moving x86's arch_ima_efi_boot_mode to <asm/ima-efi.h> and including
>> <asm/setup.h> separates that dependency from the rest of the EFI
>> interfaces. The only user is in ima_efi.c. As the file already declares
>> a default value for arch_ima_efi_boot_mode, move this define into
>> asm-generic for all other architectures.
>>
>> With arch_ima_efi_boot_mode removed from efi.h, <asm/bootparam.h> can
>> later be removed from further x86 header files.
>>
> 
> Apologies if I missed this in v1 but is the new asm-generic header
> really necessary? Could we instead turn arch_ima_efi_boot_mode into a
> function that is a static inline { return unset; } by default, but can
> be emitted out of line in one of the x86/platform/efi.c source files,
> where referring to boot_params is fine?

I cannot figure out how to do this without *something* in asm-generic or 
adding if-CONFIG_X86 guards in ima-efi.c.

But I noticed that linux/efi.h already contains 2 or 3 ifdef branches 
for x86. Would it be an option to move this code into asm/efi.h 
(including a header file in asm-generic for the non-x86 variants) and 
add the arch_ima_efi_boot_mode() helper there as well?  At least that 
wouldn't be a header for only a single define.

Best regards
Thomas

> 
> 
> 
> 
> 
>> v2:
>>          * remove extra declaration of boot_params (Ard)
>>
> 
> Please don't put the revision log here, but below the --- so that 'git
> am' will ignore it.
> 
> 
>> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
>> ---
>>   arch/x86/include/asm/efi.h       |  3 ---
>>   arch/x86/include/asm/ima-efi.h   | 11 +++++++++++
>>   include/asm-generic/Kbuild       |  1 +
>>   include/asm-generic/ima-efi.h    | 16 ++++++++++++++++
>>   security/integrity/ima/ima_efi.c |  5 +----
>>   5 files changed, 29 insertions(+), 7 deletions(-)
>>   create mode 100644 arch/x86/include/asm/ima-efi.h
>>   create mode 100644 include/asm-generic/ima-efi.h
>>
>> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
>> index c4555b269a1b..99f31176c892 100644
>> --- a/arch/x86/include/asm/efi.h
>> +++ b/arch/x86/include/asm/efi.h
>> @@ -418,9 +418,6 @@ extern int __init efi_memmap_split_count(efi_memory_desc_t *md,
>>   extern void __init efi_memmap_insert(struct efi_memory_map *old_memmap,
>>                                       void *buf, struct efi_mem_range *mem);
>>
>> -#define arch_ima_efi_boot_mode \
>> -       ({ extern struct boot_params boot_params; boot_params.secure_boot; })
>> -
>>   #ifdef CONFIG_EFI_RUNTIME_MAP
>>   int efi_get_runtime_map_size(void);
>>   int efi_get_runtime_map_desc_size(void);
>> diff --git a/arch/x86/include/asm/ima-efi.h b/arch/x86/include/asm/ima-efi.h
>> new file mode 100644
>> index 000000000000..b4d904e66b39
>> --- /dev/null
>> +++ b/arch/x86/include/asm/ima-efi.h
>> @@ -0,0 +1,11 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef _ASM_X86_IMA_EFI_H
>> +#define _ASM_X86_IMA_EFI_H
>> +
>> +#include <asm/setup.h>
>> +
>> +#define arch_ima_efi_boot_mode boot_params.secure_boot
>> +
>> +#include <asm-generic/ima-efi.h>
>> +
>> +#endif /* _ASM_X86_IMA_EFI_H */
>> diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
>> index def242528b1d..4fd16e71e8cd 100644
>> --- a/include/asm-generic/Kbuild
>> +++ b/include/asm-generic/Kbuild
>> @@ -26,6 +26,7 @@ mandatory-y += ftrace.h
>>   mandatory-y += futex.h
>>   mandatory-y += hardirq.h
>>   mandatory-y += hw_irq.h
>> +mandatory-y += ima-efi.h
>>   mandatory-y += io.h
>>   mandatory-y += irq.h
>>   mandatory-y += irq_regs.h
>> diff --git a/include/asm-generic/ima-efi.h b/include/asm-generic/ima-efi.h
>> new file mode 100644
>> index 000000000000..f87f5edef440
>> --- /dev/null
>> +++ b/include/asm-generic/ima-efi.h
>> @@ -0,0 +1,16 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +
>> +#ifndef __ASM_GENERIC_IMA_EFI_H_
>> +#define __ASM_GENERIC_IMA_EFI_H_
>> +
>> +#include <linux/efi.h>
>> +
>> +/*
>> + * Only include this header file from your architecture's <asm/ima-efi.h>.
>> + */
>> +
>> +#ifndef arch_ima_efi_boot_mode
>> +#define arch_ima_efi_boot_mode efi_secureboot_mode_unset
>> +#endif
>> +
>> +#endif /* __ASM_GENERIC_FB_H_ */
>> diff --git a/security/integrity/ima/ima_efi.c b/security/integrity/ima/ima_efi.c
>> index 138029bfcce1..56bbee271cec 100644
>> --- a/security/integrity/ima/ima_efi.c
>> +++ b/security/integrity/ima/ima_efi.c
>> @@ -6,10 +6,7 @@
>>   #include <linux/module.h>
>>   #include <linux/ima.h>
>>   #include <asm/efi.h>
>> -
>> -#ifndef arch_ima_efi_boot_mode
>> -#define arch_ima_efi_boot_mode efi_secureboot_mode_unset
>> -#endif
>> +#include <asm/ima-efi.h>
>>
>>   static enum efi_secureboot_mode get_sb_mode(void)
>>   {
>> --
>> 2.43.0
>>
>>

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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