1 // SPDX-License-Identifier: GPL-2.0
2
3 #include <linux/spinlock.h>
4 #include <linux/percpu.h>
5 #include <linux/kallsyms.h>
6 #include <linux/kcore.h>
7 #include <linux/pgtable.h>
8
9 #include <asm/cpu_entry_area.h>
10 #include <asm/fixmap.h>
11 #include <asm/desc.h>
12 #include <asm/kasan.h>
13 #include <asm/setup.h>
14
15 static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);
16
17 #ifdef CONFIG_X86_64
18 static DEFINE_PER_CPU_PAGE_ALIGNED(struct exception_stacks, exception_stacks);
19 DEFINE_PER_CPU(struct cea_exception_stacks*, cea_exception_stacks);
20
21 static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, _cea_offset);
22
23 static __always_inline unsigned int cea_offset(unsigned int cpu)
24 {
25 return per_cpu(_cea_offset, cpu);
26 }
27
28 static __init void init_cea_offsets(void)
29 {
30 unsigned int max_cea;
31 unsigned int i, j;
32
33 if (!kaslr_enabled()) {
34 for_each_possible_cpu(i)
35 per_cpu(_cea_offset, i) = i;
36 return;
37 }
38
39 max_cea = (CPU_ENTRY_AREA_MAP_SIZE - PAGE_SIZE) / CPU_ENTRY_AREA_SIZE;
40
41 /* O(sodding terrible) */
42 for_each_possible_cpu(i) {
43 unsigned int cea;
44
45 again:
46 cea = get_random_u32_below(max_cea);
47
48 for_each_possible_cpu(j) {
49 if (cea_offset(j) == cea)
50 goto again;
51
52 if (i == j)
53 break;
54 }
55
56 per_cpu(_cea_offset, i) = cea;
57 }
58 }
59 #else /* !X86_64 */
60 DECLARE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack);
61
62 static __always_inline unsigned int cea_offset(unsigned int cpu)
63 {
64 return cpu;
65 }
66 static inline void init_cea_offsets(void) { }
67 #endif
68
69 /* Is called from entry code, so must be noinstr */
70 noinstr struct cpu_entry_area *get_cpu_entry_area(int cpu)
71 {
72 unsigned long va = CPU_ENTRY_AREA_PER_CPU + cea_offset(cpu) * CPU_ENTRY_AREA_SIZE;
73 BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0);
74
75 return (struct cpu_entry_area *) va;
76 }
77 EXPORT_SYMBOL(get_cpu_entry_area);
78
79 void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
80 {
81 unsigned long va = (unsigned long) cea_vaddr;
82 pte_t pte = pfn_pte(pa >> PAGE_SHIFT, flags);
83
84 /*
85 * The cpu_entry_area is shared between the user and kernel
86 * page tables. All of its ptes can safely be global.
87 * _PAGE_GLOBAL gets reused to help indicate PROT_NONE for
88 * non-present PTEs, so be careful not to set it in that
89 * case to avoid confusion.
90 */
91 if (boot_cpu_has(X86_FEATURE_PGE) &&
92 (pgprot_val(flags) & _PAGE_PRESENT))
93 pte = pte_set_flags(pte, _PAGE_GLOBAL);
94
95 set_pte_vaddr(va, pte);
96 }
97
98 static void __init
99 cea_map_percpu_pages(void *cea_vaddr, void *ptr, int pages, pgprot_t prot)
100 {
101 for ( ; pages; pages--, cea_vaddr+= PAGE_SIZE, ptr += PAGE_SIZE)
102 cea_set_pte(cea_vaddr, per_cpu_ptr_to_phys(ptr), prot);
103 }
104
105 static void __init percpu_setup_debug_store(unsigned int cpu)
106 {
107 #ifdef CONFIG_CPU_SUP_INTEL
108 unsigned int npages;
109 void *cea;
110
111 if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
112 return;
113
114 cea = &get_cpu_entry_area(cpu)->cpu_debug_store;
115 npages = sizeof(struct debug_store) / PAGE_SIZE;
116 BUILD_BUG_ON(sizeof(struct debug_store) % PAGE_SIZE != 0);
117 cea_map_percpu_pages(cea, &per_cpu(cpu_debug_store, cpu), npages,
118 PAGE_KERNEL);
119
120 cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers;
121 /*
122 * Force the population of PMDs for not yet allocated per cpu
123 * memory like debug store buffers.
124 */
125 npages = sizeof(struct debug_store_buffers) / PAGE_SIZE;
126 for (; npages; npages--, cea += PAGE_SIZE)
127 cea_set_pte(cea, 0, PAGE_NONE);
128 #endif
129 }
130
131 #ifdef CONFIG_X86_64
132
133 #define cea_map_stack(name) do { \
134 npages = sizeof(estacks->name## _stack) / PAGE_SIZE; \
135 cea_map_percpu_pages(cea->estacks.name## _stack, \
136 estacks->name## _stack, npages, PAGE_KERNEL); \
137 } while (0)
138
139 static void __init percpu_setup_exception_stacks(unsigned int cpu)
140 {
141 struct exception_stacks *estacks = per_cpu_ptr(&exception_stacks, cpu);
142 struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
143 unsigned int npages;
144
145 BUILD_BUG_ON(sizeof(exception_stacks) % PAGE_SIZE != 0);
146
147 per_cpu(cea_exception_stacks, cpu) = &cea->estacks;
148
149 /*
150 * The exceptions stack mappings in the per cpu area are protected
151 * by guard pages so each stack must be mapped separately. DB2 is
152 * not mapped; it just exists to catch triple nesting of #DB.
153 */
154 cea_map_stack(DF);
155 cea_map_stack(NMI);
156 cea_map_stack(DB);
157 cea_map_stack(MCE);
158
159 if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
160 if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
161 cea_map_stack(VC);
162 cea_map_stack(VC2);
163 }
164 }
165 }
166 #else
167 static inline void percpu_setup_exception_stacks(unsigned int cpu)
168 {
169 struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
170
171 cea_map_percpu_pages(&cea->doublefault_stack,
172 &per_cpu(doublefault_stack, cpu), 1, PAGE_KERNEL);
173 }
174 #endif
175
176 /* Setup the fixmap mappings only once per-processor */
177 static void __init setup_cpu_entry_area(unsigned int cpu)
178 {
179 struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
180 #ifdef CONFIG_X86_64
181 /* On 64-bit systems, we use a read-only fixmap GDT and TSS. */
182 pgprot_t gdt_prot = PAGE_KERNEL_RO;
183 pgprot_t tss_prot = PAGE_KERNEL_RO;
184 #else
185 /*
186 * On 32-bit systems, the GDT cannot be read-only because
187 * our double fault handler uses a task gate, and entering through
188 * a task gate needs to change an available TSS to busy. If the
189 * GDT is read-only, that will triple fault. The TSS cannot be
190 * read-only because the CPU writes to it on task switches.
191 */
192 pgprot_t gdt_prot = PAGE_KERNEL;
193 pgprot_t tss_prot = PAGE_KERNEL;
194 #endif
195
196 kasan_populate_shadow_for_vaddr(cea, CPU_ENTRY_AREA_SIZE,
197 early_cpu_to_node(cpu));
198
199 cea_set_pte(&cea->gdt, get_cpu_gdt_paddr(cpu), gdt_prot);
200
201 cea_map_percpu_pages(&cea->entry_stack_page,
202 per_cpu_ptr(&entry_stack_storage, cpu), 1,
203 PAGE_KERNEL);
204
205 /*
206 * The Intel SDM says (Volume 3, 7.2.1):
207 *
208 * Avoid placing a page boundary in the part of the TSS that the
209 * processor reads during a task switch (the first 104 bytes). The
210 * processor may not correctly perform address translations if a
211 * boundary occurs in this area. During a task switch, the processor
212 * reads and writes into the first 104 bytes of each TSS (using
213 * contiguous physical addresses beginning with the physical address
214 * of the first byte of the TSS). So, after TSS access begins, if
215 * part of the 104 bytes is not physically contiguous, the processor
216 * will access incorrect information without generating a page-fault
217 * exception.
218 *
219 * There are also a lot of errata involving the TSS spanning a page
220 * boundary. Assert that we're not doing that.
221 */
222 BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
223 offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
224 BUILD_BUG_ON(sizeof(struct tss_struct) % PAGE_SIZE != 0);
225 /*
226 * VMX changes the host TR limit to 0x67 after a VM exit. This is
227 * okay, since 0x67 covers the size of struct x86_hw_tss. Make sure
228 * that this is correct.
229 */
230 BUILD_BUG_ON(offsetof(struct tss_struct, x86_tss) != 0);
231 BUILD_BUG_ON(sizeof(struct x86_hw_tss) != 0x68);
232
233 cea_map_percpu_pages(&cea->tss, &per_cpu(cpu_tss_rw, cpu),
234 sizeof(struct tss_struct) / PAGE_SIZE, tss_prot);
235
236 #ifdef CONFIG_X86_32
237 per_cpu(cpu_entry_area, cpu) = cea;
238 #endif
239
240 percpu_setup_exception_stacks(cpu);
241
242 percpu_setup_debug_store(cpu);
243 }
244
245 static __init void setup_cpu_entry_area_ptes(void)
246 {
247 #ifdef CONFIG_X86_32
248 unsigned long start, end;
249
250 /* The +1 is for the readonly IDT: */
251 BUILD_BUG_ON((CPU_ENTRY_AREA_PAGES+1)*PAGE_SIZE != CPU_ENTRY_AREA_MAP_SIZE);
252 BUG_ON(CPU_ENTRY_AREA_BASE & ~PMD_MASK);
253
254 start = CPU_ENTRY_AREA_BASE;
255 end = start + CPU_ENTRY_AREA_MAP_SIZE;
256
257 /* Careful here: start + PMD_SIZE might wrap around */
258 for (; start < end && start >= CPU_ENTRY_AREA_BASE; start += PMD_SIZE)
259 populate_extra_pte(start);
260 #endif
261 }
262
263 void __init setup_cpu_entry_areas(void)
264 {
265 unsigned int cpu;
266
267 init_cea_offsets();
268
269 setup_cpu_entry_area_ptes();
270
271 for_each_possible_cpu(cpu)
272 setup_cpu_entry_area(cpu);
273
274 /*
275 * This is the last essential update to swapper_pgdir which needs
276 * to be synchronized to initial_page_table on 32bit.
277 */
278 sync_initial_page_table();
279 }
280
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