arch/arm/kernel/vdso.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Adapted from arm64 version.
   4  *
   5  * Copyright (C) 2012 ARM Limited
   6  * Copyright (C) 2015 Mentor Graphics Corporation.
   7  */
   8
   9 #include <linux/cache.h>
  10 #include <linux/elf.h>
  11 #include <linux/err.h>
  12 #include <linux/kernel.h>
  13 #include <linux/mm.h>
  14 #include <linux/of.h>
  15 #include <linux/printk.h>
  16 #include <linux/slab.h>
  17 #include <linux/timekeeper_internal.h>
  18 #include <linux/vmalloc.h>
  19 #include <asm/arch_timer.h>
  20 #include <asm/barrier.h>
  21 #include <asm/cacheflush.h>
  22 #include <asm/page.h>
  23 #include <asm/vdso.h>
  24 #include <asm/vdso_datapage.h>
  25 #include <clocksource/arm_arch_timer.h>
  26 #include <vdso/helpers.h>
  27 #include <vdso/vsyscall.h>
  28
  29 #define MAX_SYMNAME     64
  30
  31 static struct page **vdso_text_pagelist;
  32
  33 extern char vdso_start[], vdso_end[];
  34
  35 /* Total number of pages needed for the data and text portions of the VDSO. */
  36 unsigned int vdso_total_pages __ro_after_init;
  37
  38 /*
  39  * The VDSO data page.
  40  */
  41 static union vdso_data_store vdso_data_store __page_aligned_data;
  42 struct vdso_data *vdso_data = vdso_data_store.data;
  43
  44 static struct page *vdso_data_page __ro_after_init;
  45 static const struct vm_special_mapping vdso_data_mapping = {
  46         .name = "[vvar]",
  47         .pages = &vdso_data_page,
  48 };
  49
  50 static int vdso_mremap(const struct vm_special_mapping *sm,
  51                 struct vm_area_struct *new_vma)
  52 {
  53         unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
  54         unsigned long vdso_size;
  55
  56         /* without VVAR page */
  57         vdso_size = (vdso_total_pages - 1) << PAGE_SHIFT;
  58
  59         if (vdso_size != new_size)
  60                 return -EINVAL;
  61
  62         current->mm->context.vdso = new_vma->vm_start;
  63
  64         return 0;
  65 }
  66
  67 static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
  68         .name = "[vdso]",
  69         .mremap = vdso_mremap,
  70 };
  71
  72 struct elfinfo {
  73         Elf32_Ehdr      *hdr;           /* ptr to ELF */
  74         Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
  75         unsigned long   dynsymsize;     /* size of .dynsym section */
  76         char            *dynstr;        /* ptr to .dynstr section */
  77 };
  78
  79 /* Cached result of boot-time check for whether the arch timer exists,
  80  * and if so, whether the virtual counter is useable.
  81  */
  82 bool cntvct_ok __ro_after_init;
  83
  84 static bool __init cntvct_functional(void)
  85 {
  86         struct device_node *np;
  87         bool ret = false;
  88
  89         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
  90                 goto out;
  91
  92         /* The arm_arch_timer core should export
  93          * arch_timer_use_virtual or similar so we don't have to do
  94          * this.
  95          */
  96         np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
  97         if (!np)
  98                 np = of_find_compatible_node(NULL, NULL, "arm,armv8-timer");
  99         if (!np)
 100                 goto out_put;
 101
 102         if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
 103                 goto out_put;
 104
 105         ret = true;
 106
 107 out_put:
 108         of_node_put(np);
 109 out:
 110         return ret;
 111 }
 112
 113 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 114                                   unsigned long *size)
 115 {
 116         Elf32_Shdr *sechdrs;
 117         unsigned int i;
 118         char *secnames;
 119
 120         /* Grab section headers and strings so we can tell who is who */
 121         sechdrs = (void *)ehdr + ehdr->e_shoff;
 122         secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;
 123
 124         /* Find the section they want */
 125         for (i = 1; i < ehdr->e_shnum; i++) {
 126                 if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 127                         if (size)
 128                                 *size = sechdrs[i].sh_size;
 129                         return (void *)ehdr + sechdrs[i].sh_offset;
 130                 }
 131         }
 132
 133         if (size)
 134                 *size = 0;
 135         return NULL;
 136 }
 137
 138 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 139 {
 140         unsigned int i;
 141
 142         for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 143                 char name[MAX_SYMNAME], *c;
 144
 145                 if (lib->dynsym[i].st_name == 0)
 146                         continue;
 147                 strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
 148                         MAX_SYMNAME);
 149                 c = strchr(name, '@');
 150                 if (c)
 151                         *c = 0;
 152                 if (strcmp(symname, name) == 0)
 153                         return &lib->dynsym[i];
 154         }
 155         return NULL;
 156 }
 157
 158 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 159 {
 160         Elf32_Sym *sym;
 161
 162         sym = find_symbol(lib, symname);
 163         if (!sym)
 164                 return;
 165
 166         sym->st_name = 0;
 167 }
 168
 169 static void __init patch_vdso(void *ehdr)
 170 {
 171         struct elfinfo einfo;
 172
 173         einfo = (struct elfinfo) {
 174                 .hdr = ehdr,
 175         };
 176
 177         einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 178         einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);
 179
 180         /* If the virtual counter is absent or non-functional we don't
 181          * want programs to incur the slight additional overhead of
 182          * dispatching through the VDSO only to fall back to syscalls.
 183          */
 184         if (!cntvct_ok) {
 185                 vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 186                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 187         }
 188 }
 189
 190 static int __init vdso_init(void)
 191 {
 192         unsigned int text_pages;
 193         int i;
 194
 195         if (memcmp(vdso_start, "\177ELF", 4)) {
 196                 pr_err("VDSO is not a valid ELF object!\n");
 197                 return -ENOEXEC;
 198         }
 199
 200         text_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
 201
 202         /* Allocate the VDSO text pagelist */
 203         vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 204                                      GFP_KERNEL);
 205         if (vdso_text_pagelist == NULL)
 206                 return -ENOMEM;
 207
 208         /* Grab the VDSO data page. */
 209         vdso_data_page = virt_to_page(vdso_data);
 210
 211         /* Grab the VDSO text pages. */
 212         for (i = 0; i < text_pages; i++) {
 213                 struct page *page;
 214
 215                 page = virt_to_page(vdso_start + i * PAGE_SIZE);
 216                 vdso_text_pagelist[i] = page;
 217         }
 218
 219         vdso_text_mapping.pages = vdso_text_pagelist;
 220
 221         vdso_total_pages = 1; /* for the data/vvar page */
 222         vdso_total_pages += text_pages;
 223
 224         cntvct_ok = cntvct_functional();
 225
 226         patch_vdso(vdso_start);
 227
 228         return 0;
 229 }
 230 arch_initcall(vdso_init);
 231
 232 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 233 {
 234         struct vm_area_struct *vma;
 235
 236         vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 237                                        VM_READ | VM_MAYREAD,
 238                                        &vdso_data_mapping);
 239
 240         return PTR_ERR_OR_ZERO(vma);
 241 }
 242
 243 /* assumes mmap_sem is write-locked */
 244 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 245 {
 246         struct vm_area_struct *vma;
 247         unsigned long len;
 248
 249         mm->context.vdso = 0;
 250
 251         if (vdso_text_pagelist == NULL)
 252                 return;
 253
 254         if (install_vvar(mm, addr))
 255                 return;
 256
 257         /* Account for vvar page. */
 258         addr += PAGE_SIZE;
 259         len = (vdso_total_pages - 1) << PAGE_SHIFT;
 260
 261         vma = _install_special_mapping(mm, addr, len,
 262                 VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 263                 &vdso_text_mapping);
 264
 265         if (!IS_ERR(vma))
 266                 mm->context.vdso = addr;
 267 }
 268