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

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