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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 | // SPDX-License-Identifier: GPL-2.0 #include <linux/kernel.h> #include <linux/errno.h> #include <linux/sched.h> #include <linux/user.h> #include <linux/regset.h> #include <linux/syscalls.h> #include <linux/nospec.h> #include <linux/uaccess.h> #include <asm/desc.h> #include <asm/ldt.h> #include <asm/processor.h> #include <asm/proto.h> #include <asm/gsseg.h> #include "tls.h" /* * sys_alloc_thread_area: get a yet unused TLS descriptor index. */ static int get_free_idx(void) { struct thread_struct *t = ¤t->thread; int idx; for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++) if (desc_empty(&t->tls_array[idx])) return idx + GDT_ENTRY_TLS_MIN; return -ESRCH; } static bool tls_desc_okay(const struct user_desc *info) { /* * For historical reasons (i.e. no one ever documented how any * of the segmentation APIs work), user programs can and do * assume that a struct user_desc that's all zeros except for * entry_number means "no segment at all". This never actually * worked. In fact, up to Linux 3.19, a struct user_desc like * this would create a 16-bit read-write segment with base and * limit both equal to zero. * * That was close enough to "no segment at all" until we * hardened this function to disallow 16-bit TLS segments. Fix * it up by interpreting these zeroed segments the way that they * were almost certainly intended to be interpreted. * * The correct way to ask for "no segment at all" is to specify * a user_desc that satisfies LDT_empty. To keep everything * working, we accept both. * * Note that there's a similar kludge in modify_ldt -- look at * the distinction between modes 1 and 0x11. */ if (LDT_empty(info) || LDT_zero(info)) return true; /* * espfix is required for 16-bit data segments, but espfix * only works for LDT segments. */ if (!info->seg_32bit) return false; /* Only allow data segments in the TLS array. */ if (info->contents > 1) return false; /* * Non-present segments with DPL 3 present an interesting attack * surface. The kernel should handle such segments correctly, * but TLS is very difficult to protect in a sandbox, so prevent * such segments from being created. * * If userspace needs to remove a TLS entry, it can still delete * it outright. */ if (info->seg_not_present) return false; return true; } static void set_tls_desc(struct task_struct *p, int idx, const struct user_desc *info, int n) { struct thread_struct *t = &p->thread; struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN]; int cpu; /* * We must not get preempted while modifying the TLS. */ cpu = get_cpu(); while (n-- > 0) { if (LDT_empty(info) || LDT_zero(info)) memset(desc, 0, sizeof(*desc)); else fill_ldt(desc, info); ++info; ++desc; } if (t == ¤t->thread) load_TLS(t, cpu); put_cpu(); } /* * Set a given TLS descriptor: */ int do_set_thread_area(struct task_struct *p, int idx, struct user_desc __user *u_info, int can_allocate) { struct user_desc info; unsigned short __maybe_unused sel, modified_sel; if (copy_from_user(&info, u_info, sizeof(info))) return -EFAULT; if (!tls_desc_okay(&info)) return -EINVAL; if (idx == -1) idx = info.entry_number; /* * index -1 means the kernel should try to find and * allocate an empty descriptor: */ if (idx == -1 && can_allocate) { idx = get_free_idx(); if (idx < 0) return idx; if (put_user(idx, &u_info->entry_number)) return -EFAULT; } if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) return -EINVAL; set_tls_desc(p, idx, &info, 1); /* * If DS, ES, FS, or GS points to the modified segment, forcibly * refresh it. Only needed on x86_64 because x86_32 reloads them * on return to user mode. */ modified_sel = (idx << 3) | 3; if (p == current) { #ifdef CONFIG_X86_64 savesegment(ds, sel); if (sel == modified_sel) loadsegment(ds, sel); savesegment(es, sel); if (sel == modified_sel) loadsegment(es, sel); savesegment(fs, sel); if (sel == modified_sel) loadsegment(fs, sel); #endif savesegment(gs, sel); if (sel == modified_sel) load_gs_index(sel); } else { #ifdef CONFIG_X86_64 if (p->thread.fsindex == modified_sel) p->thread.fsbase = info.base_addr; if (p->thread.gsindex == modified_sel) p->thread.gsbase = info.base_addr; #endif } return 0; } SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info) { return do_set_thread_area(current, -1, u_info, 1); } /* * Get the current Thread-Local Storage area: */ static void fill_user_desc(struct user_desc *info, int idx, const struct desc_struct *desc) { memset(info, 0, sizeof(*info)); info->entry_number = idx; info->base_addr = get_desc_base(desc); info->limit = get_desc_limit(desc); info->seg_32bit = desc->d; info->contents = desc->type >> 2; info->read_exec_only = !(desc->type & 2); info->limit_in_pages = desc->g; info->seg_not_present = !desc->p; info->useable = desc->avl; #ifdef CONFIG_X86_64 info->lm = desc->l; #endif } int do_get_thread_area(struct task_struct *p, int idx, struct user_desc __user *u_info) { struct user_desc info; int index; if (idx == -1 && get_user(idx, &u_info->entry_number)) return -EFAULT; if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) return -EINVAL; index = idx - GDT_ENTRY_TLS_MIN; index = array_index_nospec(index, GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN + 1); fill_user_desc(&info, idx, &p->thread.tls_array[index]); if (copy_to_user(u_info, &info, sizeof(info))) return -EFAULT; return 0; } SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info) { return do_get_thread_area(current, -1, u_info); } int regset_tls_active(struct task_struct *target, const struct user_regset *regset) { struct thread_struct *t = &target->thread; int n = GDT_ENTRY_TLS_ENTRIES; while (n > 0 && desc_empty(&t->tls_array[n - 1])) --n; return n; } int regset_tls_get(struct task_struct *target, const struct user_regset *regset, struct membuf to) { const struct desc_struct *tls; struct user_desc v; int pos; for (pos = 0, tls = target->thread.tls_array; to.left; pos++, tls++) { fill_user_desc(&v, GDT_ENTRY_TLS_MIN + pos, tls); membuf_write(&to, &v, sizeof(v)); } return 0; } int regset_tls_set(struct task_struct *target, const struct user_regset *regset, unsigned int pos, unsigned int count, const void *kbuf, const void __user *ubuf) { struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES]; const struct user_desc *info; int i; if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) || (pos % sizeof(struct user_desc)) != 0 || (count % sizeof(struct user_desc)) != 0) return -EINVAL; if (kbuf) info = kbuf; else if (__copy_from_user(infobuf, ubuf, count)) return -EFAULT; else info = infobuf; for (i = 0; i < count / sizeof(struct user_desc); i++) if (!tls_desc_okay(info + i)) return -EINVAL; set_tls_desc(target, GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)), info, count / sizeof(struct user_desc)); return 0; } |