arch/arm/kernel/vdso.c

   1 /*
   2  * Adapted from arm64 version.
   3  *
   4  * Copyright (C) 2012 ARM Limited
   5  * Copyright (C) 2015 Mentor Graphics Corporation.
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <linux/cache.h>
  21 #include <linux/elf.h>
  22 #include <linux/err.h>
  23 #include <linux/kernel.h>
  24 #include <linux/mm.h>
  25 #include <linux/of.h>
  26 #include <linux/printk.h>
  27 #include <linux/slab.h>
  28 #include <linux/timekeeper_internal.h>
  29 #include <linux/vmalloc.h>
  30 #include <asm/arch_timer.h>
  31 #include <asm/barrier.h>
  32 #include <asm/cacheflush.h>
  33 #include <asm/page.h>
  34 #include <asm/vdso.h>
  35 #include <asm/vdso_datapage.h>
  36 #include <clocksource/arm_arch_timer.h>
  37
  38 #define MAX_SYMNAME     64
  39
  40 static struct page **vdso_text_pagelist;
  41
  42 extern char vdso_start[], vdso_end[];
  43
  44 /* Total number of pages needed for the data and text portions of the VDSO. */
  45 unsigned int vdso_total_pages __ro_after_init;
  46
  47 /*
  48  * The VDSO data page.
  49  */
  50 static union vdso_data_store vdso_data_store __page_aligned_data;
  51 static struct vdso_data *vdso_data = &vdso_data_store.data;
  52
  53 static struct page *vdso_data_page __ro_after_init;
  54 static const struct vm_special_mapping vdso_data_mapping = {
  55         .name = "[vvar]",
  56         .pages = &vdso_data_page,
  57 };
  58
  59 static int vdso_mremap(const struct vm_special_mapping *sm,
  60                 struct vm_area_struct *new_vma)
  61 {
  62         unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
  63         unsigned long vdso_size;
  64
  65         /* without VVAR page */
  66         vdso_size = (vdso_total_pages - 1) << PAGE_SHIFT;
  67
  68         if (vdso_size != new_size)
  69                 return -EINVAL;
  70
  71         current->mm->context.vdso = new_vma->vm_start;
  72
  73         return 0;
  74 }
  75
  76 static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
  77         .name = "[vdso]",
  78         .mremap = vdso_mremap,
  79 };
  80
  81 struct elfinfo {
  82         Elf32_Ehdr      *hdr;           /* ptr to ELF */
  83         Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
  84         unsigned long   dynsymsize;     /* size of .dynsym section */
  85         char            *dynstr;        /* ptr to .dynstr section */
  86 };
  87
  88 /* Cached result of boot-time check for whether the arch timer exists,
  89  * and if so, whether the virtual counter is useable.
  90  */
  91 static bool cntvct_ok __ro_after_init;
  92
  93 static bool __init cntvct_functional(void)
  94 {
  95         struct device_node *np;
  96         bool ret = false;
  97
  98         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
  99                 goto out;
 100
 101         /* The arm_arch_timer core should export
 102          * arch_timer_use_virtual or similar so we don't have to do
 103          * this.
 104          */
 105         np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
 106         if (!np)
 107                 goto out_put;
 108
 109         if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
 110                 goto out_put;
 111
 112         ret = true;
 113
 114 out_put:
 115         of_node_put(np);
 116 out:
 117         return ret;
 118 }
 119
 120 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 121                                   unsigned long *size)
 122 {
 123         Elf32_Shdr *sechdrs;
 124         unsigned int i;
 125         char *secnames;
 126
 127         /* Grab section headers and strings so we can tell who is who */
 128         sechdrs = (void *)ehdr + ehdr->e_shoff;
 129         secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;
 130
 131         /* Find the section they want */
 132         for (i = 1; i < ehdr->e_shnum; i++) {
 133                 if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 134                         if (size)
 135                                 *size = sechdrs[i].sh_size;
 136                         return (void *)ehdr + sechdrs[i].sh_offset;
 137                 }
 138         }
 139
 140         if (size)
 141                 *size = 0;
 142         return NULL;
 143 }
 144
 145 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 146 {
 147         unsigned int i;
 148
 149         for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 150                 char name[MAX_SYMNAME], *c;
 151
 152                 if (lib->dynsym[i].st_name == 0)
 153                         continue;
 154                 strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
 155                         MAX_SYMNAME);
 156                 c = strchr(name, '@');
 157                 if (c)
 158                         *c = 0;
 159                 if (strcmp(symname, name) == 0)
 160                         return &lib->dynsym[i];
 161         }
 162         return NULL;
 163 }
 164
 165 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 166 {
 167         Elf32_Sym *sym;
 168
 169         sym = find_symbol(lib, symname);
 170         if (!sym)
 171                 return;
 172
 173         sym->st_name = 0;
 174 }
 175
 176 static void __init patch_vdso(void *ehdr)
 177 {
 178         struct elfinfo einfo;
 179
 180         einfo = (struct elfinfo) {
 181                 .hdr = ehdr,
 182         };
 183
 184         einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 185         einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);
 186
 187         /* If the virtual counter is absent or non-functional we don't
 188          * want programs to incur the slight additional overhead of
 189          * dispatching through the VDSO only to fall back to syscalls.
 190          */
 191         if (!cntvct_ok) {
 192                 vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 193                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 194         }
 195 }
 196
 197 static int __init vdso_init(void)
 198 {
 199         unsigned int text_pages;
 200         int i;
 201
 202         if (memcmp(vdso_start, "\177ELF", 4)) {
 203                 pr_err("VDSO is not a valid ELF object!\n");
 204                 return -ENOEXEC;
 205         }
 206
 207         text_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
 208         pr_debug("vdso: %i text pages at base %p\n", text_pages, vdso_start);
 209
 210         /* Allocate the VDSO text pagelist */
 211         vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 212                                      GFP_KERNEL);
 213         if (vdso_text_pagelist == NULL)
 214                 return -ENOMEM;
 215
 216         /* Grab the VDSO data page. */
 217         vdso_data_page = virt_to_page(vdso_data);
 218
 219         /* Grab the VDSO text pages. */
 220         for (i = 0; i < text_pages; i++) {
 221                 struct page *page;
 222
 223                 page = virt_to_page(vdso_start + i * PAGE_SIZE);
 224                 vdso_text_pagelist[i] = page;
 225         }
 226
 227         vdso_text_mapping.pages = vdso_text_pagelist;
 228
 229         vdso_total_pages = 1; /* for the data/vvar page */
 230         vdso_total_pages += text_pages;
 231
 232         cntvct_ok = cntvct_functional();
 233
 234         patch_vdso(vdso_start);
 235
 236         return 0;
 237 }
 238 arch_initcall(vdso_init);
 239
 240 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 241 {
 242         struct vm_area_struct *vma;
 243
 244         vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 245                                        VM_READ | VM_MAYREAD,
 246                                        &vdso_data_mapping);
 247
 248         return PTR_ERR_OR_ZERO(vma);
 249 }
 250
 251 /* assumes mmap_sem is write-locked */
 252 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 253 {
 254         struct vm_area_struct *vma;
 255         unsigned long len;
 256
 257         mm->context.vdso = 0;
 258
 259         if (vdso_text_pagelist == NULL)
 260                 return;
 261
 262         if (install_vvar(mm, addr))
 263                 return;
 264
 265         /* Account for vvar page. */
 266         addr += PAGE_SIZE;
 267         len = (vdso_total_pages - 1) << PAGE_SHIFT;
 268
 269         vma = _install_special_mapping(mm, addr, len,
 270                 VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 271                 &vdso_text_mapping);
 272
 273         if (!IS_ERR(vma))
 274                 mm->context.vdso = addr;
 275 }
 276
 277 static void vdso_write_begin(struct vdso_data *vdata)
 278 {
 279         ++vdso_data->seq_count;
 280         smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
 281 }
 282
 283 static void vdso_write_end(struct vdso_data *vdata)
 284 {
 285         smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
 286         ++vdso_data->seq_count;
 287 }
 288
 289 static bool tk_is_cntvct(const struct timekeeper *tk)
 290 {
 291         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 292                 return false;
 293
 294         if (!tk->tkr_mono.clock->archdata.vdso_direct)
 295                 return false;
 296
 297         return true;
 298 }
 299
 300 /**
 301  * update_vsyscall - update the vdso data page
 302  *
 303  * Increment the sequence counter, making it odd, indicating to
 304  * userspace that an update is in progress.  Update the fields used
 305  * for coarse clocks and, if the architected system timer is in use,
 306  * the fields used for high precision clocks.  Increment the sequence
 307  * counter again, making it even, indicating to userspace that the
 308  * update is finished.
 309  *
 310  * Userspace is expected to sample seq_count before reading any other
 311  * fields from the data page.  If seq_count is odd, userspace is
 312  * expected to wait until it becomes even.  After copying data from
 313  * the page, userspace must sample seq_count again; if it has changed
 314  * from its previous value, userspace must retry the whole sequence.
 315  *
 316  * Calls to update_vsyscall are serialized by the timekeeping core.
 317  */
 318 void update_vsyscall(struct timekeeper *tk)
 319 {
 320         struct timespec64 *wtm = &tk->wall_to_monotonic;
 321
 322         if (!cntvct_ok) {
 323                 /* The entry points have been zeroed, so there is no
 324                  * point in updating the data page.
 325                  */
 326                 return;
 327         }
 328
 329         vdso_write_begin(vdso_data);
 330
 331         vdso_data->tk_is_cntvct                 = tk_is_cntvct(tk);
 332         vdso_data->xtime_coarse_sec             = tk->xtime_sec;
 333         vdso_data->xtime_coarse_nsec            = (u32)(tk->tkr_mono.xtime_nsec >>
 334                                                         tk->tkr_mono.shift);
 335         vdso_data->wtm_clock_sec                = wtm->tv_sec;
 336         vdso_data->wtm_clock_nsec               = wtm->tv_nsec;
 337
 338         if (vdso_data->tk_is_cntvct) {
 339                 vdso_data->cs_cycle_last        = tk->tkr_mono.cycle_last;
 340                 vdso_data->xtime_clock_sec      = tk->xtime_sec;
 341                 vdso_data->xtime_clock_snsec    = tk->tkr_mono.xtime_nsec;
 342                 vdso_data->cs_mult              = tk->tkr_mono.mult;
 343                 vdso_data->cs_shift             = tk->tkr_mono.shift;
 344                 vdso_data->cs_mask              = tk->tkr_mono.mask;
 345         }
 346
 347         vdso_write_end(vdso_data);
 348
 349         flush_dcache_page(virt_to_page(vdso_data));
 350 }
 351
 352 void update_vsyscall_tz(void)
 353 {
 354         vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
 355         vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
 356         flush_dcache_page(virt_to_page(vdso_data));
 357 }