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