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         current->mm->context.vdso = new_vma->vm_start;
  54
  55         return 0;
  56 }
  57
  58 static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
  59         .name = "[vdso]",
  60         .mremap = vdso_mremap,
  61 };
  62
  63 struct elfinfo {
  64         Elf32_Ehdr      *hdr;           /* ptr to ELF */
  65         Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
  66         unsigned long   dynsymsize;     /* size of .dynsym section */
  67         char            *dynstr;        /* ptr to .dynstr section */
  68 };
  69
  70 /* Cached result of boot-time check for whether the arch timer exists,
  71  * and if so, whether the virtual counter is useable.
  72  */
  73 bool cntvct_ok __ro_after_init;
  74
  75 static bool __init cntvct_functional(void)
  76 {
  77         struct device_node *np;
  78         bool ret = false;
  79
  80         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
  81                 goto out;
  82
  83         /* The arm_arch_timer core should export
  84          * arch_timer_use_virtual or similar so we don't have to do
  85          * this.
  86          */
  87         np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
  88         if (!np)
  89                 np = of_find_compatible_node(NULL, NULL, "arm,armv8-timer");
  90         if (!np)
  91                 goto out_put;
  92
  93         if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
  94                 goto out_put;
  95
  96         ret = true;
  97
  98 out_put:
  99         of_node_put(np);
 100 out:
 101         return ret;
 102 }
 103
 104 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 105                                   unsigned long *size)
 106 {
 107         Elf32_Shdr *sechdrs;
 108         unsigned int i;
 109         char *secnames;
 110
 111         /* Grab section headers and strings so we can tell who is who */
 112         sechdrs = (void *)ehdr + ehdr->e_shoff;
 113         secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;
 114
 115         /* Find the section they want */
 116         for (i = 1; i < ehdr->e_shnum; i++) {
 117                 if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 118                         if (size)
 119                                 *size = sechdrs[i].sh_size;
 120                         return (void *)ehdr + sechdrs[i].sh_offset;
 121                 }
 122         }
 123
 124         if (size)
 125                 *size = 0;
 126         return NULL;
 127 }
 128
 129 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 130 {
 131         unsigned int i;
 132
 133         for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 134                 char name[MAX_SYMNAME], *c;
 135
 136                 if (lib->dynsym[i].st_name == 0)
 137                         continue;
 138                 strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
 139                         MAX_SYMNAME);
 140                 c = strchr(name, '@');
 141                 if (c)
 142                         *c = 0;
 143                 if (strcmp(symname, name) == 0)
 144                         return &lib->dynsym[i];
 145         }
 146         return NULL;
 147 }
 148
 149 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 150 {
 151         Elf32_Sym *sym;
 152
 153         sym = find_symbol(lib, symname);
 154         if (!sym)
 155                 return;
 156
 157         sym->st_name = 0;
 158 }
 159
 160 static void __init patch_vdso(void *ehdr)
 161 {
 162         struct elfinfo einfo;
 163
 164         einfo = (struct elfinfo) {
 165                 .hdr = ehdr,
 166         };
 167
 168         einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 169         einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);
 170
 171         /* If the virtual counter is absent or non-functional we don't
 172          * want programs to incur the slight additional overhead of
 173          * dispatching through the VDSO only to fall back to syscalls.
 174          */
 175         if (!cntvct_ok) {
 176                 vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 177                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 178                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime64");
 179         }
 180 }
 181
 182 static int __init vdso_init(void)
 183 {
 184         unsigned int text_pages;
 185         int i;
 186
 187         if (memcmp(vdso_start, "\177ELF", 4)) {
 188                 pr_err("VDSO is not a valid ELF object!\n");
 189                 return -ENOEXEC;
 190         }
 191
 192         text_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
 193
 194         /* Allocate the VDSO text pagelist */
 195         vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 196                                      GFP_KERNEL);
 197         if (vdso_text_pagelist == NULL)
 198                 return -ENOMEM;
 199
 200         /* Grab the VDSO data page. */
 201         vdso_data_page = virt_to_page(vdso_data);
 202
 203         /* Grab the VDSO text pages. */
 204         for (i = 0; i < text_pages; i++) {
 205                 struct page *page;
 206
 207                 page = virt_to_page(vdso_start + i * PAGE_SIZE);
 208                 vdso_text_pagelist[i] = page;
 209         }
 210
 211         vdso_text_mapping.pages = vdso_text_pagelist;
 212
 213         vdso_total_pages = 1; /* for the data/vvar page */
 214         vdso_total_pages += text_pages;
 215
 216         cntvct_ok = cntvct_functional();
 217
 218         patch_vdso(vdso_start);
 219
 220         return 0;
 221 }
 222 arch_initcall(vdso_init);
 223
 224 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 225 {
 226         struct vm_area_struct *vma;
 227
 228         vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 229                                        VM_READ | VM_MAYREAD,
 230                                        &vdso_data_mapping);
 231
 232         return PTR_ERR_OR_ZERO(vma);
 233 }
 234
 235 /* assumes mmap_lock is write-locked */
 236 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 237 {
 238         struct vm_area_struct *vma;
 239         unsigned long len;
 240
 241         mm->context.vdso = 0;
 242
 243         if (vdso_text_pagelist == NULL)
 244                 return;
 245
 246         if (install_vvar(mm, addr))
 247                 return;
 248
 249         /* Account for vvar page. */
 250         addr += PAGE_SIZE;
 251         len = (vdso_total_pages - 1) << PAGE_SHIFT;
 252
 253         vma = _install_special_mapping(mm, addr, len,
 254                 VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 255                 &vdso_text_mapping);
 256
 257         if (!IS_ERR(vma))
 258                 mm->context.vdso = addr;
 259 }
 260