1#include <linux/efi.h>
  2#include <asm/e820/types.h>
  3#include <asm/processor.h>
  4#include <asm/efi.h>
  5#include "pgtable.h"
  6#include "../string.h"
  7
  8/*
  9 * __force_order is used by special_insns.h asm code to force instruction
 10 * serialization.
 11 *
 12 * It is not referenced from the code, but GCC < 5 with -fPIE would fail
 13 * due to an undefined symbol. Define it to make these ancient GCCs work.
 14 */
 15unsigned long __force_order;
 16
 17#define BIOS_START_MIN		0x20000U	/* 128K, less than this is insane */
 18#define BIOS_START_MAX		0x9f000U	/* 640K, absolute maximum */
 19
 20struct paging_config {
 21	unsigned long trampoline_start;
 22	unsigned long l5_required;
 23};
 24
 25/* Buffer to preserve trampoline memory */
 26static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
 27
 28/*
 29 * Trampoline address will be printed by extract_kernel() for debugging
 30 * purposes.
 31 *
 32 * Avoid putting the pointer into .bss as it will be cleared between
 33 * paging_prepare() and extract_kernel().
 34 */
 35unsigned long *trampoline_32bit __section(.data);
 36
 37extern struct boot_params *boot_params;
 38int cmdline_find_option_bool(const char *option);
 39
 40static unsigned long find_trampoline_placement(void)
 41{
 42	unsigned long bios_start = 0, ebda_start = 0;
 43	struct boot_e820_entry *entry;
 44	char *signature;
 45	int i;
 46
 47	/*
 48	 * Find a suitable spot for the trampoline.
 49	 * This code is based on reserve_bios_regions().
 50	 */
 51
 52	/*
 53	 * EFI systems may not provide legacy ROM. The memory may not be mapped
 54	 * at all.
 55	 *
 56	 * Only look for values in the legacy ROM for non-EFI system.
 57	 */
 58	signature = (char *)&boot_params->efi_info.efi_loader_signature;
 59	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
 60	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
 61		ebda_start = *(unsigned short *)0x40e << 4;
 62		bios_start = *(unsigned short *)0x413 << 10;
 63	}
 64
 65	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
 66		bios_start = BIOS_START_MAX;
 67
 68	if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)
 69		bios_start = ebda_start;
 70
 71	bios_start = round_down(bios_start, PAGE_SIZE);
 72
 73	/* Find the first usable memory region under bios_start. */
 74	for (i = boot_params->e820_entries - 1; i >= 0; i--) {
 75		unsigned long new = bios_start;
 76
 77		entry = &boot_params->e820_table[i];
 78
 79		/* Skip all entries above bios_start. */
 80		if (bios_start <= entry->addr)
 81			continue;
 82
 83		/* Skip non-RAM entries. */
 84		if (entry->type != E820_TYPE_RAM)
 85			continue;
 86
 87		/* Adjust bios_start to the end of the entry if needed. */
 88		if (bios_start > entry->addr + entry->size)
 89			new = entry->addr + entry->size;
 90
 91		/* Keep bios_start page-aligned. */
 92		new = round_down(new, PAGE_SIZE);
 93
 94		/* Skip the entry if it's too small. */
 95		if (new - TRAMPOLINE_32BIT_SIZE < entry->addr)
 96			continue;
 97
 98		/* Protect against underflow. */
 99		if (new - TRAMPOLINE_32BIT_SIZE > bios_start)
100			break;
101
102		bios_start = new;
103		break;
104	}
105
106	/* Place the trampoline just below the end of low memory */
107	return bios_start - TRAMPOLINE_32BIT_SIZE;
108}
109
110struct paging_config paging_prepare(void *rmode)
111{
112	struct paging_config paging_config = {};
113
114	/* Initialize boot_params. Required for cmdline_find_option_bool(). */
115	boot_params = rmode;
116
117	/*
118	 * Check if LA57 is desired and supported.
119	 *
120	 * There are several parts to the check:
121	 *   - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y
122	 *   - if user asked to disable 5-level paging: no5lvl in cmdline
123	 *   - if the machine supports 5-level paging:
124	 *     + CPUID leaf 7 is supported
125	 *     + the leaf has the feature bit set
126	 *
127	 * That's substitute for boot_cpu_has() in early boot code.
128	 */
129	if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
130			!cmdline_find_option_bool("no5lvl") &&
131			native_cpuid_eax(0) >= 7 &&
132			(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
133		paging_config.l5_required = 1;
134	}
135
136	paging_config.trampoline_start = find_trampoline_placement();
137
138	trampoline_32bit = (unsigned long *)paging_config.trampoline_start;
139
140	/* Preserve trampoline memory */
141	memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
142
143	/* Clear trampoline memory first */
144	memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
145
146	/* Copy trampoline code in place */
147	memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
148			&trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
149
150	/*
151	 * The code below prepares page table in trampoline memory.
152	 *
153	 * The new page table will be used by trampoline code for switching
154	 * from 4- to 5-level paging or vice versa.
155	 *
156	 * If switching is not required, the page table is unused: trampoline
157	 * code wouldn't touch CR3.
158	 */
159
160	/*
161	 * We are not going to use the page table in trampoline memory if we
162	 * are already in the desired paging mode.
163	 */
164	if (paging_config.l5_required == !!(native_read_cr4() & X86_CR4_LA57))
165		goto out;
166
167	if (paging_config.l5_required) {
168		/*
169		 * For 4- to 5-level paging transition, set up current CR3 as
170		 * the first and the only entry in a new top-level page table.
171		 */
172		trampoline_32bit[TRAMPOLINE_32BIT_PGTABLE_OFFSET] = __native_read_cr3() | _PAGE_TABLE_NOENC;
173	} else {
174		unsigned long src;
175
176		/*
177		 * For 5- to 4-level paging transition, copy page table pointed
178		 * by first entry in the current top-level page table as our
179		 * new top-level page table.
180		 *
181		 * We cannot just point to the page table from trampoline as it
182		 * may be above 4G.
183		 */
184		src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
185		memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
186		       (void *)src, PAGE_SIZE);
187	}
188
189out:
190	return paging_config;
191}
192
193void cleanup_trampoline(void *pgtable)
194{
195	void *trampoline_pgtable;
196
197	trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
198
199	/*
200	 * Move the top level page table out of trampoline memory,
201	 * if it's there.
202	 */
203	if ((void *)__native_read_cr3() == trampoline_pgtable) {
204		memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
205		native_write_cr3((unsigned long)pgtable);
206	}
207
208	/* Restore trampoline memory */
209	memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
210}