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/elf.h>
  21 #include <linux/err.h>
  22 #include <linux/kernel.h>
  23 #include <linux/mm.h>
  24 #include <linux/of.h>
  25 #include <linux/printk.h>
  26 #include <linux/slab.h>
  27 #include <linux/timekeeper_internal.h>
  28 #include <linux/vmalloc.h>
  29 #include <asm/arch_timer.h>
  30 #include <asm/barrier.h>
  31 #include <asm/cacheflush.h>
  32 #include <asm/page.h>
  33 #include <asm/vdso.h>
  34 #include <asm/vdso_datapage.h>
  35 #include <clocksource/arm_arch_timer.h>
  36
  37 #define MAX_SYMNAME     64
  38
  39 static struct page **vdso_text_pagelist;
  40
  41 /* Total number of pages needed for the data and text portions of the VDSO. */
  42 unsigned int vdso_total_pages __read_mostly;
  43
  44 /*
  45  * The VDSO data page.
  46  */
  47 static union vdso_data_store vdso_data_store __page_aligned_data;
  48 static struct vdso_data *vdso_data = &vdso_data_store.data;
  49
  50 static struct page *vdso_data_page;
  51 static struct vm_special_mapping vdso_data_mapping = {
  52         .name = "[vvar]",
  53         .pages = &vdso_data_page,
  54 };
  55
  56 static struct vm_special_mapping vdso_text_mapping = {
  57         .name = "[vdso]",
  58 };
  59
  60 struct elfinfo {
  61         Elf32_Ehdr      *hdr;           /* ptr to ELF */
  62         Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
  63         unsigned long   dynsymsize;     /* size of .dynsym section */
  64         char            *dynstr;        /* ptr to .dynstr section */
  65 };
  66
  67 /* Cached result of boot-time check for whether the arch timer exists,
  68  * and if so, whether the virtual counter is useable.
  69  */
  70 static bool cntvct_ok __read_mostly;
  71
  72 static bool __init cntvct_functional(void)
  73 {
  74         struct device_node *np;
  75         bool ret = false;
  76
  77         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
  78                 goto out;
  79
  80         /* The arm_arch_timer core should export
  81          * arch_timer_use_virtual or similar so we don't have to do
  82          * this.
  83          */
  84         np = of_find_compatible_node(NULL, NULL, "arm,armv7-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                 strlcpy(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         }
 174 }
 175
 176 static int __init vdso_init(void)
 177 {
 178         unsigned int text_pages;
 179         int i;
 180
 181         if (memcmp(&vdso_start, "\177ELF", 4)) {
 182                 pr_err("VDSO is not a valid ELF object!\n");
 183                 return -ENOEXEC;
 184         }
 185
 186         text_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
 187         pr_debug("vdso: %i text pages at base %p\n", text_pages, &vdso_start);
 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_sem 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
 256 static void vdso_write_begin(struct vdso_data *vdata)
 257 {
 258         ++vdso_data->seq_count;
 259         smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
 260 }
 261
 262 static void vdso_write_end(struct vdso_data *vdata)
 263 {
 264         smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
 265         ++vdso_data->seq_count;
 266 }
 267
 268 static bool tk_is_cntvct(const struct timekeeper *tk)
 269 {
 270         if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 271                 return false;
 272
 273         if (strcmp(tk->tkr_mono.clock->name, "arch_sys_counter") != 0)
 274                 return false;
 275
 276         return true;
 277 }
 278
 279 /**
 280  * update_vsyscall - update the vdso data page
 281  *
 282  * Increment the sequence counter, making it odd, indicating to
 283  * userspace that an update is in progress.  Update the fields used
 284  * for coarse clocks and, if the architected system timer is in use,
 285  * the fields used for high precision clocks.  Increment the sequence
 286  * counter again, making it even, indicating to userspace that the
 287  * update is finished.
 288  *
 289  * Userspace is expected to sample seq_count before reading any other
 290  * fields from the data page.  If seq_count is odd, userspace is
 291  * expected to wait until it becomes even.  After copying data from
 292  * the page, userspace must sample seq_count again; if it has changed
 293  * from its previous value, userspace must retry the whole sequence.
 294  *
 295  * Calls to update_vsyscall are serialized by the timekeeping core.
 296  */
 297 void update_vsyscall(struct timekeeper *tk)
 298 {
 299         struct timespec64 *wtm = &tk->wall_to_monotonic;
 300
 301         if (!cntvct_ok) {
 302                 /* The entry points have been zeroed, so there is no
 303                  * point in updating the data page.
 304                  */
 305                 return;
 306         }
 307
 308         vdso_write_begin(vdso_data);
 309
 310         vdso_data->tk_is_cntvct                 = tk_is_cntvct(tk);
 311         vdso_data->xtime_coarse_sec             = tk->xtime_sec;
 312         vdso_data->xtime_coarse_nsec            = (u32)(tk->tkr_mono.xtime_nsec >>
 313                                                         tk->tkr_mono.shift);
 314         vdso_data->wtm_clock_sec                = wtm->tv_sec;
 315         vdso_data->wtm_clock_nsec               = wtm->tv_nsec;
 316
 317         if (vdso_data->tk_is_cntvct) {
 318                 vdso_data->cs_cycle_last        = tk->tkr_mono.cycle_last;
 319                 vdso_data->xtime_clock_sec      = tk->xtime_sec;
 320                 vdso_data->xtime_clock_snsec    = tk->tkr_mono.xtime_nsec;
 321                 vdso_data->cs_mult              = tk->tkr_mono.mult;
 322                 vdso_data->cs_shift             = tk->tkr_mono.shift;
 323                 vdso_data->cs_mask              = tk->tkr_mono.mask;
 324         }
 325
 326         vdso_write_end(vdso_data);
 327
 328         flush_dcache_page(virt_to_page(vdso_data));
 329 }
 330
 331 void update_vsyscall_tz(void)
 332 {
 333         vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
 334         vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
 335         flush_dcache_page(virt_to_page(vdso_data));
 336 }