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2024-05-11 04dd17822334871b23ea2862f7798fb0e0007777

 kernel/drivers/firmware/efi/libstub/random.c
..
..
@@ -1,192 +1,143 @@
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+// SPDX-License-Identifier: GPL-2.0
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2
 /*
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  * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
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- *
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- * This program is free software; you can redistribute it and/or modify
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- * it under the terms of the GNU General Public License version 2 as
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- * published by the Free Software Foundation.
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- *
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4
  */
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5
 
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 #include <linux/efi.h>
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-#include <linux/log2.h>
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7
 #include <asm/efi.h>
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8
 
14
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 #include "efistub.h"
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10
 
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-struct efi_rng_protocol {
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-	efi_status_t (*get_info)(struct efi_rng_protocol *,
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-				 unsigned long *, efi_guid_t *);
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-	efi_status_t (*get_rng)(struct efi_rng_protocol *,
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-				efi_guid_t *, unsigned long, u8 *out);
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+typedef union efi_rng_protocol efi_rng_protocol_t;
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+
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+union efi_rng_protocol {
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+	struct {
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+		efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
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+						  unsigned long *,
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+						  efi_guid_t *);
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+		efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
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+						 efi_guid_t *, unsigned long,
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+						 u8 *out);
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+	};
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+	struct {
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+		u32 get_info;
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+		u32 get_rng;
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+	} mixed_mode;
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26
 };
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27
 
23
-efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
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-				  unsigned long size, u8 *out)
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+/**
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+ * efi_get_random_bytes() - fill a buffer with random bytes
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+ * @size:	size of the buffer
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+ * @out:	caller allocated buffer to receive the random bytes
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+ *
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+ * The call will fail if either the firmware does not implement the
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+ * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
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+ * the buffer.
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+ *
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+ * Return:	status code
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+ */
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+efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
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40
 {
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41
 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
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 	efi_status_t status;
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-	struct efi_rng_protocol *rng;
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+	efi_rng_protocol_t *rng = NULL;
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44
 
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-	status = efi_call_early(locate_protocol, &rng_proto, NULL,
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-				(void **)&rng);
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+	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
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46
 	if (status != EFI_SUCCESS)
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 		return status;
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48
 
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-	return rng->get_rng(rng, NULL, size, out);
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+	return efi_call_proto(rng, get_rng, NULL, size, out);
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50
 }
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51
 
38
-/*
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- * Return the number of slots covered by this entry, i.e., the number of
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- * addresses it covers that are suitably aligned and supply enough room
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- * for the allocation.
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+/**
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+ * efi_random_get_seed() - provide random seed as configuration table
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+ *
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+ * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
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+ * saved as a configuration table which can be used as entropy by the kernel
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+ * for the initialization of its pseudo random number generator.
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+ *
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+ * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
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+ * available, the configuration table will not be installed and an error code
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+ * will be returned.
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+ *
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+ * Return:	status code
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64
  */
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-static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
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-					 unsigned long size,
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-					 unsigned long align_shift)
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-{
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-	unsigned long align = 1UL << align_shift;
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-	u64 first_slot, last_slot, region_end;
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-
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-	if (md->type != EFI_CONVENTIONAL_MEMORY)
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-		return 0;
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-
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-	region_end = min((u64)ULONG_MAX, md->phys_addr + md->num_pages*EFI_PAGE_SIZE - 1);
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-
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-	first_slot = round_up(md->phys_addr, align);
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-	last_slot = round_down(region_end - size + 1, align);
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-
58
-	if (first_slot > last_slot)
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-		return 0;
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-
61
-	return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
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-}
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-
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-/*
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- * The UEFI memory descriptors have a virtual address field that is only used
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- * when installing the virtual mapping using SetVirtualAddressMap(). Since it
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- * is unused here, we can reuse it to keep track of each descriptor's slot
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- * count.
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- */
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-#define MD_NUM_SLOTS(md)	((md)->virt_addr)
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-
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-efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
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-			      unsigned long size,
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-			      unsigned long align,
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-			      unsigned long *addr,
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-			      unsigned long random_seed)
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-{
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-	unsigned long map_size, desc_size, total_slots = 0, target_slot;
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-	unsigned long buff_size;
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-	efi_status_t status;
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-	efi_memory_desc_t *memory_map;
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-	int map_offset;
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-	struct efi_boot_memmap map;
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-
85
-	map.map =	&memory_map;
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-	map.map_size =	&map_size;
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-	map.desc_size =	&desc_size;
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-	map.desc_ver =	NULL;
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-	map.key_ptr =	NULL;
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-	map.buff_size =	&buff_size;
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-
92
-	status = efi_get_memory_map(sys_table_arg, &map);
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-	if (status != EFI_SUCCESS)
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-		return status;
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-
96
-	if (align < EFI_ALLOC_ALIGN)
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-		align = EFI_ALLOC_ALIGN;
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-
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-	/* count the suitable slots in each memory map entry */
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-	for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
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-		efi_memory_desc_t *md = (void *)memory_map + map_offset;
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-		unsigned long slots;
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-
104
-		slots = get_entry_num_slots(md, size, ilog2(align));
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-		MD_NUM_SLOTS(md) = slots;
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-		total_slots += slots;
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-	}
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-
109
-	/* find a random number between 0 and total_slots */
110
-	target_slot = (total_slots * (u16)random_seed) >> 16;
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-
112
-	/*
113
-	 * target_slot is now a value in the range [0, total_slots), and so
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-	 * it corresponds with exactly one of the suitable slots we recorded
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-	 * when iterating over the memory map the first time around.
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-	 *
117
-	 * So iterate over the memory map again, subtracting the number of
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-	 * slots of each entry at each iteration, until we have found the entry
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-	 * that covers our chosen slot. Use the residual value of target_slot
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-	 * to calculate the randomly chosen address, and allocate it directly
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-	 * using EFI_ALLOCATE_ADDRESS.
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-	 */
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-	for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
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-		efi_memory_desc_t *md = (void *)memory_map + map_offset;
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-		efi_physical_addr_t target;
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-		unsigned long pages;
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-
128
-		if (target_slot >= MD_NUM_SLOTS(md)) {
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-			target_slot -= MD_NUM_SLOTS(md);
130
-			continue;
131
-		}
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-
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-		target = round_up(md->phys_addr, align) + target_slot * align;
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-		pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
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-
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-		status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
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-					EFI_LOADER_DATA, pages, &target);
138
-		if (status == EFI_SUCCESS)
139
-			*addr = target;
140
-		break;
141
-	}
142
-
143
-	efi_call_early(free_pool, memory_map);
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-
145
-	return status;
146
-}
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-
148
-efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg)
65
+efi_status_t efi_random_get_seed(void)
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66
 {
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67
 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
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68
 	efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
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69
 	efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
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-	struct efi_rng_protocol *rng;
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-	struct linux_efi_random_seed *seed;
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+	struct linux_efi_random_seed *prev_seed, *seed = NULL;
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+	int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
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+	efi_rng_protocol_t *rng = NULL;
155
73
 	efi_status_t status;
156
74
 
157
-	status = efi_call_early(locate_protocol, &rng_proto, NULL,
158
-				(void **)&rng);
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+	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
159
76
 	if (status != EFI_SUCCESS)
160
77
 		return status;
161
78
 
162
-	status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
163
-				sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
164
-				(void **)&seed);
165
-	if (status != EFI_SUCCESS)
166
-		return status;
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+	/*
80
+	 * Check whether a seed was provided by a prior boot stage. In that
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+	 * case, instead of overwriting it, let's create a new buffer that can
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+	 * hold both, and concatenate the existing and the new seeds.
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+	 * Note that we should read the seed size with caution, in case the
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+	 * table got corrupted in memory somehow.
85
+	 */
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+	prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID);
87
+	if (prev_seed && prev_seed->size <= 512U) {
88
+		prev_seed_size = prev_seed->size;
89
+		seed_size += prev_seed_size;
90
+	}
167
91
 
168
-	status = rng->get_rng(rng, &rng_algo_raw, EFI_RANDOM_SEED_SIZE,
169
-			      seed->bits);
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+	/*
93
+	 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
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+	 * allocation will survive a kexec reboot (although we refresh the seed
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+	 * beforehand)
96
+	 */
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+	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
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+			     struct_size(seed, bits, seed_size),
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+			     (void **)&seed);
100
+	if (status != EFI_SUCCESS) {
101
+		efi_warn("Failed to allocate memory for RNG seed.\n");
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+		goto err_warn;
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+	}
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+
105
+	status = efi_call_proto(rng, get_rng, &rng_algo_raw,
106
+				EFI_RANDOM_SEED_SIZE, seed->bits);
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+
170
108
 	if (status == EFI_UNSUPPORTED)
171
109
 		/*
172
110
 		 * Use whatever algorithm we have available if the raw algorithm
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111
 		 * is not implemented.
174
112
 		 */
175
-		status = rng->get_rng(rng, NULL, EFI_RANDOM_SEED_SIZE,
176
-				      seed->bits);
113
+		status = efi_call_proto(rng, get_rng, NULL,
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+					EFI_RANDOM_SEED_SIZE, seed->bits);
177
115
 
178
116
 	if (status != EFI_SUCCESS)
179
117
 		goto err_freepool;
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118
 
181
-	seed->size = EFI_RANDOM_SEED_SIZE;
182
-	status = efi_call_early(install_configuration_table, &rng_table_guid,
183
-				seed);
119
+	seed->size = seed_size;
120
+	if (prev_seed_size)
121
+		memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
122
+		       prev_seed_size);
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+
124
+	status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
184
125
 	if (status != EFI_SUCCESS)
185
126
 		goto err_freepool;
186
127
 
128
+	if (prev_seed_size) {
129
+		/* wipe and free the old seed if we managed to install the new one */
130
+		memzero_explicit(prev_seed->bits, prev_seed_size);
131
+		efi_bs_call(free_pool, prev_seed);
132
+	}
187
133
 	return EFI_SUCCESS;
188
134
 
189
135
 err_freepool:
190
-	efi_call_early(free_pool, seed);
136
+	memzero_explicit(seed, struct_size(seed, bits, seed_size));
137
+	efi_bs_call(free_pool, seed);
138
+	efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n");
139
+err_warn:
140
+	if (prev_seed)
141
+		efi_warn("Retaining bootloader-supplied seed only");
191
142
 	return status;
192
143
 }