1 // SPDX-License-Identifier: GPL-2.0-only
2 // Copyright 2023 Google LLC
3 // Author: Ard Biesheuvel <ardb@google.com>
4
5 #include <linux/init.h>
6 #include <linux/libfdt.h>
7 #include <linux/linkage.h>
8 #include <linux/types.h>
9 #include <linux/sizes.h>
10 #include <linux/string.h>
11
12 #include <asm/memory.h>
13 #include <asm/pgalloc.h>
14 #include <asm/pgtable.h>
15 #include <asm/tlbflush.h>
16
17 #include "pi.h"
18
19 extern const u8 __eh_frame_start[], __eh_frame_end[];
20
21 extern void idmap_cpu_replace_ttbr1(void *pgdir);
22
map_segment(pgd_t * pg_dir,u64 * pgd,u64 va_offset,void * start,void * end,pgprot_t prot,bool may_use_cont,int root_level)23 static void __init map_segment(pgd_t *pg_dir, u64 *pgd, u64 va_offset,
24 void *start, void *end, pgprot_t prot,
25 bool may_use_cont, int root_level)
26 {
27 map_range(pgd, ((u64)start + va_offset) & ~PAGE_OFFSET,
28 ((u64)end + va_offset) & ~PAGE_OFFSET, (u64)start,
29 prot, root_level, (pte_t *)pg_dir, may_use_cont, 0);
30 }
31
unmap_segment(pgd_t * pg_dir,u64 va_offset,void * start,void * end,int root_level)32 static void __init unmap_segment(pgd_t *pg_dir, u64 va_offset, void *start,
33 void *end, int root_level)
34 {
35 map_segment(pg_dir, NULL, va_offset, start, end, __pgprot(0),
36 false, root_level);
37 }
38
map_kernel(u64 kaslr_offset,u64 va_offset,int root_level)39 static void __init map_kernel(u64 kaslr_offset, u64 va_offset, int root_level)
40 {
41 bool enable_scs = IS_ENABLED(CONFIG_UNWIND_PATCH_PAC_INTO_SCS);
42 bool twopass = IS_ENABLED(CONFIG_RELOCATABLE);
43 u64 pgdp = (u64)init_pg_dir + PAGE_SIZE;
44 pgprot_t text_prot = PAGE_KERNEL_ROX;
45 pgprot_t data_prot = PAGE_KERNEL;
46 pgprot_t prot;
47
48 /*
49 * External debuggers may need to write directly to the text mapping to
50 * install SW breakpoints. Allow this (only) when explicitly requested
51 * with rodata=off.
52 */
53 if (arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_RODATA_OFF))
54 text_prot = PAGE_KERNEL_EXEC;
55
56 /*
57 * We only enable the shadow call stack dynamically if we are running
58 * on a system that does not implement PAC or BTI. PAC and SCS provide
59 * roughly the same level of protection, and BTI relies on the PACIASP
60 * instructions serving as landing pads, preventing us from patching
61 * those instructions into something else.
62 */
63 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL) && cpu_has_pac())
64 enable_scs = false;
65
66 if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && cpu_has_bti()) {
67 enable_scs = false;
68
69 /*
70 * If we have a CPU that supports BTI and a kernel built for
71 * BTI then mark the kernel executable text as guarded pages
72 * now so we don't have to rewrite the page tables later.
73 */
74 text_prot = __pgprot_modify(text_prot, PTE_GP, PTE_GP);
75 }
76
77 /* Map all code read-write on the first pass if needed */
78 twopass |= enable_scs;
79 prot = twopass ? data_prot : text_prot;
80
81 map_segment(init_pg_dir, &pgdp, va_offset, _stext, _etext, prot,
82 !twopass, root_level);
83 map_segment(init_pg_dir, &pgdp, va_offset, __start_rodata,
84 __inittext_begin, data_prot, false, root_level);
85 map_segment(init_pg_dir, &pgdp, va_offset, __inittext_begin,
86 __inittext_end, prot, false, root_level);
87 map_segment(init_pg_dir, &pgdp, va_offset, __initdata_begin,
88 __initdata_end, data_prot, false, root_level);
89 map_segment(init_pg_dir, &pgdp, va_offset, _data, _end, data_prot,
90 true, root_level);
91 dsb(ishst);
92
93 idmap_cpu_replace_ttbr1(init_pg_dir);
94
95 if (twopass) {
96 if (IS_ENABLED(CONFIG_RELOCATABLE))
97 relocate_kernel(kaslr_offset);
98
99 if (enable_scs) {
100 scs_patch(__eh_frame_start + va_offset,
101 __eh_frame_end - __eh_frame_start);
102 asm("ic ialluis");
103
104 dynamic_scs_is_enabled = true;
105 }
106
107 /*
108 * Unmap the text region before remapping it, to avoid
109 * potential TLB conflicts when creating the contiguous
110 * descriptors.
111 */
112 unmap_segment(init_pg_dir, va_offset, _stext, _etext,
113 root_level);
114 dsb(ishst);
115 isb();
116 __tlbi(vmalle1);
117 isb();
118
119 /*
120 * Remap these segments with different permissions
121 * No new page table allocations should be needed
122 */
123 map_segment(init_pg_dir, NULL, va_offset, _stext, _etext,
124 text_prot, true, root_level);
125 map_segment(init_pg_dir, NULL, va_offset, __inittext_begin,
126 __inittext_end, text_prot, false, root_level);
127 }
128
129 /* Copy the root page table to its final location */
130 memcpy((void *)swapper_pg_dir + va_offset, init_pg_dir, PAGE_SIZE);
131 dsb(ishst);
132 idmap_cpu_replace_ttbr1(swapper_pg_dir);
133 }
134
set_ttbr0_for_lpa2(u64 ttbr)135 static void noinline __section(".idmap.text") set_ttbr0_for_lpa2(u64 ttbr)
136 {
137 u64 sctlr = read_sysreg(sctlr_el1);
138 u64 tcr = read_sysreg(tcr_el1) | TCR_DS;
139
140 asm(" msr sctlr_el1, %0 ;"
141 " isb ;"
142 " msr ttbr0_el1, %1 ;"
143 " msr tcr_el1, %2 ;"
144 " isb ;"
145 " tlbi vmalle1 ;"
146 " dsb nsh ;"
147 " isb ;"
148 " msr sctlr_el1, %3 ;"
149 " isb ;"
150 :: "r"(sctlr & ~SCTLR_ELx_M), "r"(ttbr), "r"(tcr), "r"(sctlr));
151 }
152
remap_idmap_for_lpa2(void)153 static void __init remap_idmap_for_lpa2(void)
154 {
155 /* clear the bits that change meaning once LPA2 is turned on */
156 pteval_t mask = PTE_SHARED;
157
158 /*
159 * We have to clear bits [9:8] in all block or page descriptors in the
160 * initial ID map, as otherwise they will be (mis)interpreted as
161 * physical address bits once we flick the LPA2 switch (TCR.DS). Since
162 * we cannot manipulate live descriptors in that way without creating
163 * potential TLB conflicts, let's create another temporary ID map in a
164 * LPA2 compatible fashion, and update the initial ID map while running
165 * from that.
166 */
167 create_init_idmap(init_pg_dir, mask);
168 dsb(ishst);
169 set_ttbr0_for_lpa2((u64)init_pg_dir);
170
171 /*
172 * Recreate the initial ID map with the same granularity as before.
173 * Don't bother with the FDT, we no longer need it after this.
174 */
175 memset(init_idmap_pg_dir, 0,
176 (u64)init_idmap_pg_end - (u64)init_idmap_pg_dir);
177
178 create_init_idmap(init_idmap_pg_dir, mask);
179 dsb(ishst);
180
181 /* switch back to the updated initial ID map */
182 set_ttbr0_for_lpa2((u64)init_idmap_pg_dir);
183
184 /* wipe the temporary ID map from memory */
185 memset(init_pg_dir, 0, (u64)init_pg_end - (u64)init_pg_dir);
186 }
187
map_fdt(u64 fdt)188 static void __init map_fdt(u64 fdt)
189 {
190 static u8 ptes[INIT_IDMAP_FDT_SIZE] __initdata __aligned(PAGE_SIZE);
191 u64 efdt = fdt + MAX_FDT_SIZE;
192 u64 ptep = (u64)ptes;
193
194 /*
195 * Map up to MAX_FDT_SIZE bytes, but avoid overlap with
196 * the kernel image.
197 */
198 map_range(&ptep, fdt, (u64)_text > fdt ? min((u64)_text, efdt) : efdt,
199 fdt, PAGE_KERNEL, IDMAP_ROOT_LEVEL,
200 (pte_t *)init_idmap_pg_dir, false, 0);
201 dsb(ishst);
202 }
203
early_map_kernel(u64 boot_status,void * fdt)204 asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
205 {
206 static char const chosen_str[] __initconst = "/chosen";
207 u64 va_base, pa_base = (u64)&_text;
208 u64 kaslr_offset = pa_base % MIN_KIMG_ALIGN;
209 int root_level = 4 - CONFIG_PGTABLE_LEVELS;
210 int va_bits = VA_BITS;
211 int chosen;
212
213 map_fdt((u64)fdt);
214
215 /* Clear BSS and the initial page tables */
216 memset(__bss_start, 0, (u64)init_pg_end - (u64)__bss_start);
217
218 /* Parse the command line for CPU feature overrides */
219 chosen = fdt_path_offset(fdt, chosen_str);
220 init_feature_override(boot_status, fdt, chosen);
221
222 if (IS_ENABLED(CONFIG_ARM64_64K_PAGES) && !cpu_has_lva()) {
223 va_bits = VA_BITS_MIN;
224 } else if (IS_ENABLED(CONFIG_ARM64_LPA2) && !cpu_has_lpa2()) {
225 va_bits = VA_BITS_MIN;
226 root_level++;
227 }
228
229 if (va_bits > VA_BITS_MIN)
230 sysreg_clear_set(tcr_el1, TCR_T1SZ_MASK, TCR_T1SZ(va_bits));
231
232 /*
233 * The virtual KASLR displacement modulo 2MiB is decided by the
234 * physical placement of the image, as otherwise, we might not be able
235 * to create the early kernel mapping using 2 MiB block descriptors. So
236 * take the low bits of the KASLR offset from the physical address, and
237 * fill in the high bits from the seed.
238 */
239 if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
240 u64 kaslr_seed = kaslr_early_init(fdt, chosen);
241
242 if (kaslr_seed && kaslr_requires_kpti())
243 arm64_use_ng_mappings = true;
244
245 kaslr_offset |= kaslr_seed & ~(MIN_KIMG_ALIGN - 1);
246 }
247
248 if (IS_ENABLED(CONFIG_ARM64_LPA2) && va_bits > VA_BITS_MIN)
249 remap_idmap_for_lpa2();
250
251 va_base = KIMAGE_VADDR + kaslr_offset;
252 map_kernel(kaslr_offset, va_base - pa_base, root_level);
253 }
254