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                 np = of_find_compatible_node(NULL, NULL, "arm,armv8-timer");
 108         if (!np)
 109                 goto out_put;
 110
 111         if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
 112                 goto out_put;
 113
 114         ret = true;
 115
 116 out_put:
 117         of_node_put(np);
 118 out:
 119         return ret;
 120 }
 121
 122 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 123                                   unsigned long *size)
 124 {
 125         Elf32_Shdr *sechdrs;
 126         unsigned int i;
 127         char *secnames;
 128
 129         /* Grab section headers and strings so we can tell who is who */
 130         sechdrs = (void *)ehdr + ehdr->e_shoff;
 131         secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;
 132
 133         /* Find the section they want */
 134         for (i = 1; i < ehdr->e_shnum; i++) {
 135                 if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 136                         if (size)
 137                                 *size = sechdrs[i].sh_size;
 138                         return (void *)ehdr + sechdrs[i].sh_offset;
 139                 }
 140         }
 141
 142         if (size)
 143                 *size = 0;
 144         return NULL;
 145 }
 146
 147 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 148 {
 149         unsigned int i;
 150
 151         for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 152                 char name[MAX_SYMNAME], *c;
 153
 154                 if (lib->dynsym[i].st_name == 0)
 155                         continue;
 156                 strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
 157                         MAX_SYMNAME);
 158                 c = strchr(name, '@');
 159                 if (c)
 160                         *c = 0;
 161                 if (strcmp(symname, name) == 0)
 162                         return &lib->dynsym[i];
 163         }
 164         return NULL;
 165 }
 166
 167 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 168 {
 169         Elf32_Sym *sym;
 170
 171         sym = find_symbol(lib, symname);
 172         if (!sym)
 173                 return;
 174
 175         sym->st_name = 0;
 176 }
 177
 178 static void __init patch_vdso(void *ehdr)
 179 {
 180         struct elfinfo einfo;
 181
 182         einfo = (struct elfinfo) {
 183                 .hdr = ehdr,
 184         };
 185
 186         einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 187         einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);
 188
 189         /* If the virtual counter is absent or non-functional we don't
 190          * want programs to incur the slight additional overhead of
 191          * dispatching through the VDSO only to fall back to syscalls.
 192          */
 193         if (!cntvct_ok) {
 194                 vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 195                 vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 196         }
 197 }
 198
 199 static int __init vdso_init(void)
 200 {
 201         unsigned int text_pages;
 202         int i;
 203
 204         if (memcmp(vdso_start, "\177ELF", 4)) {
 205                 pr_err("VDSO is not a valid ELF object!\n");
 206                 return -ENOEXEC;
 207         }
 208
 209         text_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
 210         pr_debug("vdso: %i text pages at base %p\n", text_pages, vdso_start);
 211
 212         /* Allocate the VDSO text pagelist */
 213         vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 214                                      GFP_KERNEL);
 215         if (vdso_text_pagelist == NULL)
 216                 return -ENOMEM;
 217
 218         /* Grab the VDSO data page. */
 219         vdso_data_page = virt_to_page(vdso_data);
 220
 221         /* Grab the VDSO text pages. */
 222         for (i = 0; i < text_pages; i++) {
 223                 struct page *page;
 224
 225                 page = virt_to_page(vdso_start + i * PAGE_SIZE);
 226                 vdso_text_pagelist[i] = page;
 227         }
 228
 229         vdso_text_mapping.pages = vdso_text_pagelist;
 230
 231         vdso_total_pages = 1; /* for the data/vvar page */
 232         vdso_total_pages += text_pages;
 233
 234         cntvct_ok = cntvct_functional();
 235
 236         patch_vdso(vdso_start);
 237
 238         return 0;
 239 }
 240 arch_initcall(vdso_init);
 241
 242 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 243 {
 244         struct vm_area_struct *vma;
 245
 246         vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 247                                        VM_READ | VM_MAYREAD,
 248                                        &vdso_data_mapping);
 249
 250         return PTR_ERR_OR_ZERO(vma);
 251 }
 252
 253 /* assumes mmap_sem is write-locked */
 254 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 255 {
 256         struct vm_area_struct *vma;
 257         unsigned long len;
 258
 259         mm->context.vdso = 0;
 260
 261         if (vdso_text_pagelist == NULL)
 262                 return;
 263
 264         if (install_vvar(mm, addr))
 265                 return;
 266
 267         /* Account for vvar page. */
 268         addr += PAGE_SIZE;
 269         len = (vdso_total_pages - 1) << PAGE_SHIFT;
 270
 271         vma = _install_special_mapping(mm, addr, len,
 272                 VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 273                 &vdso_text_mapping);
 274
 275         if (!IS_ERR(vma))
 276                 mm->context.vdso = addr;
 277 }
 278
 279 static void vdso_write_begin(struct vdso_data *vdata)
 280 {
 281         ++vdso_data->seq_count;
 282         smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
 283 }
 284
 285 static void vdso_write_end(struct vdso_data *vdata)
 286 {
 287         smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
 288         ++vdso_data->seq_count;
 289 }
 290
 291 static bool tk_is_cntvct(const struct timekeeper *tk)
 292 {
 293         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 294                 return false;
 295
 296         if (!tk->tkr_mono.clock->archdata.vdso_direct)
 297                 return false;
 298
 299         return true;
 300 }
 301
 302 /**
 303  * update_vsyscall - update the vdso data page
 304  *
 305  * Increment the sequence counter, making it odd, indicating to
 306  * userspace that an update is in progress.  Update the fields used
 307  * for coarse clocks and, if the architected system timer is in use,
 308  * the fields used for high precision clocks.  Increment the sequence
 309  * counter again, making it even, indicating to userspace that the
 310  * update is finished.
 311  *
 312  * Userspace is expected to sample seq_count before reading any other
 313  * fields from the data page.  If seq_count is odd, userspace is
 314  * expected to wait until it becomes even.  After copying data from
 315  * the page, userspace must sample seq_count again; if it has changed
 316  * from its previous value, userspace must retry the whole sequence.
 317  *
 318  * Calls to update_vsyscall are serialized by the timekeeping core.
 319  */
 320 void update_vsyscall(struct timekeeper *tk)
 321 {
 322         struct timespec64 *wtm = &tk->wall_to_monotonic;
 323
 324         if (!cntvct_ok) {
 325                 /* The entry points have been zeroed, so there is no
 326                  * point in updating the data page.
 327                  */
 328                 return;
 329         }
 330
 331         vdso_write_begin(vdso_data);
 332
 333         vdso_data->tk_is_cntvct                 = tk_is_cntvct(tk);
 334         vdso_data->xtime_coarse_sec             = tk->xtime_sec;
 335         vdso_data->xtime_coarse_nsec            = (u32)(tk->tkr_mono.xtime_nsec >>
 336                                                         tk->tkr_mono.shift);
 337         vdso_data->wtm_clock_sec                = wtm->tv_sec;
 338         vdso_data->wtm_clock_nsec               = wtm->tv_nsec;
 339
 340         if (vdso_data->tk_is_cntvct) {
 341                 vdso_data->cs_cycle_last        = tk->tkr_mono.cycle_last;
 342                 vdso_data->xtime_clock_sec      = tk->xtime_sec;
 343                 vdso_data->xtime_clock_snsec    = tk->tkr_mono.xtime_nsec;
 344                 vdso_data->cs_mult              = tk->tkr_mono.mult;
 345                 vdso_data->cs_shift             = tk->tkr_mono.shift;
 346                 vdso_data->cs_mask              = tk->tkr_mono.mask;
 347         }
 348
 349         vdso_write_end(vdso_data);
 350
 351         flush_dcache_page(virt_to_page(vdso_data));
 352 }
 353
 354 void update_vsyscall_tz(void)
 355 {
 356         vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
 357         vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
 358         flush_dcache_page(virt_to_page(vdso_data));
 359 }