Re: [PATCH v4 2/3] efi: Reserve confidential computing secret area

From: Dov Murik <dovmurik@linux.ibm.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: linux-efi@vger.kernel.org, Borislav Petkov <bp@suse.de>,
	Ashish Kalra <ashish.kalra@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Andi Kleen <ak@linux.intel.com>, Andrew Scull <ascull@google.com>,
	Dave Hansen <dave.hansen@intel.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@linux.ibm.com>,
	Jim Cadden <jcadden@ibm.com>,
	Daniele Buono <dbuono@linux.vnet.ibm.com>,
	linux-coco@lists.linux.dev,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, Dov Murik <dovmurik@linux.ibm.com>
Subject: Re: [PATCH v4 2/3] efi: Reserve confidential computing secret area
Date: Wed, 20 Oct 2021 11:19:42 +0300	[thread overview]
Message-ID: <1d79190a-f023-a83c-b197-62b0514dc769@linux.ibm.com> (raw)
In-Reply-To: <YW+55YcXqUtrw4/T@kroah.com>

On 20/10/2021 9:40, Greg KH wrote:
> On Wed, Oct 20, 2021 at 06:14:07AM +0000, Dov Murik wrote:
>> When efi-stub copies an EFI-provided confidential computing (coco)
>> secret area, reserve that memory block for future use within the kernel.
>>
>> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
>> ---
>>  arch/x86/platform/efi/efi.c   |  3 +++
>>  drivers/firmware/efi/Makefile |  1 +
>>  drivers/firmware/efi/coco.c   | 41 +++++++++++++++++++++++++++++++++++
>>  drivers/firmware/efi/efi.c    |  8 +++++++
>>  include/linux/efi.h           | 10 +++++++++
>>  5 files changed, 63 insertions(+)
>>  create mode 100644 drivers/firmware/efi/coco.c
>>
>> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
>> index 147c30a81f15..1591d67e0bcd 100644
>> --- a/arch/x86/platform/efi/efi.c
>> +++ b/arch/x86/platform/efi/efi.c
>> @@ -93,6 +93,9 @@ static const unsigned long * const efi_tables[] = {
>>  #ifdef CONFIG_LOAD_UEFI_KEYS
>>  	&efi.mokvar_table,
>>  #endif
>> +#ifdef CONFIG_EFI_COCO_SECRET
>> +	&efi.coco_secret,
>> +#endif
>>  };
>>  
>>  u64 efi_setup;		/* efi setup_data physical address */
>> diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
>> index c02ff25dd477..49c4a8c0bfc4 100644
>> --- a/drivers/firmware/efi/Makefile
>> +++ b/drivers/firmware/efi/Makefile
>> @@ -32,6 +32,7 @@ obj-$(CONFIG_APPLE_PROPERTIES)		+= apple-properties.o
>>  obj-$(CONFIG_EFI_RCI2_TABLE)		+= rci2-table.o
>>  obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE)	+= embedded-firmware.o
>>  obj-$(CONFIG_LOAD_UEFI_KEYS)		+= mokvar-table.o
>> +obj-$(CONFIG_EFI_COCO_SECRET)		+= coco.o
>>  
>>  fake_map-y				+= fake_mem.o
>>  fake_map-$(CONFIG_X86)			+= x86_fake_mem.o
>> diff --git a/drivers/firmware/efi/coco.c b/drivers/firmware/efi/coco.c
>> new file mode 100644
>> index 000000000000..42f477d6188c
>> --- /dev/null
>> +++ b/drivers/firmware/efi/coco.c
>> @@ -0,0 +1,41 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Confidential computing (coco) secret area handling
>> + *
>> + * Copyright (C) 2021 IBM Corporation
>> + * Author: Dov Murik <dovmurik@linux.ibm.com>
>> + */
>> +
>> +#define pr_fmt(fmt) "efi: " fmt
>> +
>> +#include <linux/efi.h>
>> +#include <linux/init.h>
>> +#include <linux/memblock.h>
>> +#include <asm/early_ioremap.h>
>> +
>> +/*
>> + * Reserve the confidential computing secret area memory
>> + */
>> +int __init efi_coco_secret_area_reserve(void)
>> +{
>> +	struct linux_efi_coco_secret_area *secret_area;
>> +	unsigned long secret_area_size;
>> +
>> +	if (efi.coco_secret == EFI_INVALID_TABLE_ADDR)
>> +		return 0;
>> +
>> +	secret_area = early_memremap(efi.coco_secret, sizeof(*secret_area));
>> +	if (!secret_area) {
>> +		pr_err("Failed to map confidential computing secret area\n");
>> +		efi.coco_secret = EFI_INVALID_TABLE_ADDR;
>> +		return -ENOMEM;
>> +	}
>> +
>> +	secret_area_size = sizeof(*secret_area) + secret_area->size;
>> +	memblock_reserve(efi.coco_secret, secret_area_size);
>> +
>> +	pr_info("Reserved memory of EFI-provided confidential computing secret area");
> 
> When kernel code works properly, it is quiet.  Why do you need to print
> this out at every boot?
> 

My kernel is not so quiet at the info loglevel; specifically from efi I 
see these prints (third log line added by this patch):

[    0.000000] efi: EFI v2.70 by EDK II
[    0.000000] efi: SMBIOS=0x7f541000 ACPI=0x7f77e000 ACPI 2.0=0x7f77e014 MEMATTR=0x7ea0c018 CocoSecret=0x7ea0b018
[    0.000000] efi: Reserved memory of EFI-provided confidential computing secret area

This print is useful to understand that both OVMF (EFI) and kernel support
the confidential computing secret area.

>> +
>> +	early_memunmap(secret_area, sizeof(*secret_area));
>> +	return 0;
>> +}
> 
> And again, when is this memory freed when shutting down?
> 

It is currently not freed.  I tried to look for such memory freeing of
other EFI-provided memory areas (such as efi.tpm_final_log) and couldn't
find them.  Can you please share pointers/examples of how to do that?

Thanks,
-Dov