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/vmalloc.h>
  18 #include <asm/arch_timer.h>
  19 #include <asm/barrier.h>
  20 #include <asm/cacheflush.h>
  21 #include <asm/page.h>
  22 #include <asm/vdso.h>
  23 #include <clocksource/arm_arch_timer.h>
  24 #include <vdso/helpers.h>
  25 #include <vdso/vsyscall.h>
  26
  27 #define MAX_SYMNAME     64
  28
  29 static struct page **vdso_text_pagelist;
  30
  31 extern char vdso_start[], vdso_end[];
  32
  33 /* Total number of pages needed for the data and text portions of the VDSO. */
  34 unsigned int vdso_total_pages __ro_after_init;
  35
  36 static union vdso_data_store vdso_data_store __page_aligned_data;
  37 struct vdso_data *vdso_data = vdso_data_store.data;
  38
  39 static struct page *vdso_data_page __ro_after_init;
  40 static const struct vm_special_mapping vdso_data_mapping = {
  41         .name = "[vvar]",
  42         .pages = &vdso_data_page,
  43 };
  44
  45 static int vdso_mremap(const struct vm_special_mapping *sm,
  46                 struct vm_area_struct *new_vma)
  47 {
  48         current->mm->context.vdso = new_vma->vm_start;
  49
  50         return 0;
  51 }
  52
  53 static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
  54         .name = "[vdso]",
  55         .mremap = vdso_mremap,
  56 };
  57
  58 struct elfinfo {
  59         Elf32_Ehdr      *hdr;           /* ptr to ELF */
  60         Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
  61         unsigned long   dynsymsize;     /* size of .dynsym section */
  62         char            *dynstr;        /* ptr to .dynstr section */
  63 };
  64
  65 /* Cached result of boot-time check for whether the arch timer exists,
  66  * and if so, whether the virtual counter is useable.
  67  */
  68 bool cntvct_ok __ro_after_init;
  69
  70 static bool __init cntvct_functional(void)
  71 {
  72         struct device_node *np;
  73         bool ret = false;
  74
  75         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
  76                 goto out;
  77
  78         /* The arm_arch_timer core should export
  79          * arch_timer_use_virtual or similar so we don't have to do
  80          * this.
  81          */
  82         np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
  83         if (!np)
  84                 np = of_find_compatible_node(NULL, NULL, "arm,armv8-timer");
  85         if (!np)
  86                 goto out_put;
  87
  88         if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
  89                 goto out_put;
  90
  91         ret = true;
  92
  93 out_put:
  94         of_node_put(np);
  95 out:
  96         return ret;
  97 }
  98
  99 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 100                                   unsigned long *size)
 101 {
 102         Elf32_Shdr *sechdrs;
 103         unsigned int i;
 104         char *secnames;
 105
 106         /* Grab section headers and strings so we can tell who is who */
 107         sechdrs = (void *)ehdr + ehdr->e_shoff;
 108         secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;
 109
 110         /* Find the section they want */
 111         for (i = 1; i < ehdr->e_shnum; i++) {
 112                 if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 113                         if (size)
 114                                 *size = sechdrs[i].sh_size;
 115                         return (void *)ehdr + sechdrs[i].sh_offset;
 116                 }
 117         }
 118
 119         if (size)
 120                 *size = 0;
 121         return NULL;
 122 }
 123
 124 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 125 {
 126         unsigned int i;
 127
 128         for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 129                 char name[MAX_SYMNAME], *c;
 130
 131                 if (lib->dynsym[i].st_name == 0)
 132                         continue;
 133                 strscpy(name, lib->dynstr + lib->dynsym[i].st_name,
 134                         MAX_SYMNAME);
 135                 c = strchr(name, '@');
 136                 if (c)
 137                         *c = 0;
 138                 if (strcmp(symname, name) == 0)
 139                         return &lib->dynsym[i];
 140         }
 141         return NULL;
 142 }
 143
 144 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 145 {
 146         Elf32_Sym *sym;
 147
 148         sym = find_symbol(lib, symname);
 149         if (!sym)
 150                 return;
 151
 152         sym->st_name = 0;
 153 }
 154
 155 static void __init patch_vdso(void *ehdr)
 156 {
 157         struct elfinfo einfo;
 158
 159         einfo = (struct elfinfo) {
 160                 .hdr = ehdr,
 161         };
 162
 163         einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 164         einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);
 165
 166         /* If the virtual counter is absent or non-functional we don't
 167          * want programs to incur the slight additional overhead of
 168          * dispatching through the VDSO only to fall back to syscalls.
 169          */
 170         if (!cntvct_ok) {
 171                 vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 172                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 173                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime64");
 174         }
 175 }
 176
 177 static int __init vdso_init(void)
 178 {
 179         unsigned int text_pages;
 180         int i;
 181
 182         if (memcmp(vdso_start, "\177ELF", 4)) {
 183                 pr_err("VDSO is not a valid ELF object!\n");
 184                 return -ENOEXEC;
 185         }
 186
 187         text_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
 188
 189         /* Allocate the VDSO text pagelist */
 190         vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 191                                      GFP_KERNEL);
 192         if (vdso_text_pagelist == NULL)
 193                 return -ENOMEM;
 194
 195         /* Grab the VDSO data page. */
 196         vdso_data_page = virt_to_page(vdso_data);
 197
 198         /* Grab the VDSO text pages. */
 199         for (i = 0; i < text_pages; i++) {
 200                 struct page *page;
 201
 202                 page = virt_to_page(vdso_start + i * PAGE_SIZE);
 203                 vdso_text_pagelist[i] = page;
 204         }
 205
 206         vdso_text_mapping.pages = vdso_text_pagelist;
 207
 208         vdso_total_pages = 1; /* for the data/vvar page */
 209         vdso_total_pages += text_pages;
 210
 211         cntvct_ok = cntvct_functional();
 212
 213         patch_vdso(vdso_start);
 214
 215         return 0;
 216 }
 217 arch_initcall(vdso_init);
 218
 219 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 220 {
 221         struct vm_area_struct *vma;
 222
 223         vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 224                                        VM_READ | VM_MAYREAD,
 225                                        &vdso_data_mapping);
 226
 227         return PTR_ERR_OR_ZERO(vma);
 228 }
 229
 230 /* assumes mmap_lock is write-locked */
 231 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 232 {
 233         struct vm_area_struct *vma;
 234         unsigned long len;
 235
 236         mm->context.vdso = 0;
 237
 238         if (vdso_text_pagelist == NULL)
 239                 return;
 240
 241         if (install_vvar(mm, addr))
 242                 return;
 243
 244         /* Account for vvar page. */
 245         addr += PAGE_SIZE;
 246         len = (vdso_total_pages - 1) << PAGE_SHIFT;
 247
 248         vma = _install_special_mapping(mm, addr, len,
 249                 VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 250                 &vdso_text_mapping);
 251
 252         if (!IS_ERR(vma))
 253                 mm->context.vdso = addr;
 254 }
 255