59 lines
1.8 KiB
C
59 lines
1.8 KiB
C
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/*
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* TPM handling.
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*
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* Copyright (C) 2016 CoreOS, Inc
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* Copyright (C) 2017 Google, Inc.
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* Matthew Garrett <mjg59@google.com>
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*
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* This file is part of the Linux kernel, and is made available under the
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* terms of the GNU General Public License version 2.
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*/
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#include <linux/efi.h>
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#include <asm/efi.h>
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#include "efistub.h"
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static const efi_char16_t efi_MemoryOverWriteRequest_name[] = {
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'M', 'e', 'm', 'o', 'r', 'y', 'O', 'v', 'e', 'r', 'w', 'r', 'i', 't',
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'e', 'R', 'e', 'q', 'u', 'e', 's', 't', 'C', 'o', 'n', 't', 'r', 'o',
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'l', 0
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};
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#define MEMORY_ONLY_RESET_CONTROL_GUID \
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EFI_GUID(0xe20939be, 0x32d4, 0x41be, 0xa1, 0x50, 0x89, 0x7f, 0x85, 0xd4, 0x98, 0x29)
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#define get_efi_var(name, vendor, ...) \
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efi_call_runtime(get_variable, \
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(efi_char16_t *)(name), (efi_guid_t *)(vendor), \
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__VA_ARGS__)
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#define set_efi_var(name, vendor, ...) \
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efi_call_runtime(set_variable, \
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(efi_char16_t *)(name), (efi_guid_t *)(vendor), \
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__VA_ARGS__)
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/*
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* Enable reboot attack mitigation. This requests that the firmware clear the
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* RAM on next reboot before proceeding with boot, ensuring that any secrets
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* are cleared. If userland has ensured that all secrets have been removed
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* from RAM before reboot it can simply reset this variable.
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*/
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void efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg)
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{
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u8 val = 1;
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efi_guid_t var_guid = MEMORY_ONLY_RESET_CONTROL_GUID;
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efi_status_t status;
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unsigned long datasize = 0;
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status = get_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
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NULL, &datasize, NULL);
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if (status == EFI_NOT_FOUND)
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return;
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set_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
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EFI_VARIABLE_NON_VOLATILE |
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EFI_VARIABLE_BOOTSERVICE_ACCESS |
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EFI_VARIABLE_RUNTIME_ACCESS, sizeof(val), &val);
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}
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