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