arch/powerpc/kernel/security.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 //
   3 // Security related flags and so on.
   4 //
   5 // Copyright 2018, Michael Ellerman, IBM Corporation.
   6
   7 #include <linux/cpu.h>
   8 #include <linux/kernel.h>
   9 #include <linux/device.h>
  10 #include <linux/nospec.h>
  11 #include <linux/prctl.h>
  12 #include <linux/seq_buf.h>
  13
  14 #include <asm/asm-prototypes.h>
  15 #include <asm/code-patching.h>
  16 #include <asm/debugfs.h>
  17 #include <asm/security_features.h>
  18 #include <asm/setup.h>
  19 #include <asm/inst.h>
  20
  21
  22 u64 powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;
  23
  24 enum count_cache_flush_type {
  25         COUNT_CACHE_FLUSH_NONE  = 0x1,
  26         COUNT_CACHE_FLUSH_SW    = 0x2,
  27         COUNT_CACHE_FLUSH_HW    = 0x4,
  28 };
  29 static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NONE;
  30 static bool link_stack_flush_enabled;
  31
  32 bool barrier_nospec_enabled;
  33 static bool no_nospec;
  34 static bool btb_flush_enabled;
  35 #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
  36 static bool no_spectrev2;
  37 #endif
  38
  39 static void enable_barrier_nospec(bool enable)
  40 {
  41         barrier_nospec_enabled = enable;
  42         do_barrier_nospec_fixups(enable);
  43 }
  44
  45 void setup_barrier_nospec(void)
  46 {
  47         bool enable;
  48
  49         /*
  50          * It would make sense to check SEC_FTR_SPEC_BAR_ORI31 below as well.
  51          * But there's a good reason not to. The two flags we check below are
  52          * both are enabled by default in the kernel, so if the hcall is not
  53          * functional they will be enabled.
  54          * On a system where the host firmware has been updated (so the ori
  55          * functions as a barrier), but on which the hypervisor (KVM/Qemu) has
  56          * not been updated, we would like to enable the barrier. Dropping the
  57          * check for SEC_FTR_SPEC_BAR_ORI31 achieves that. The only downside is
  58          * we potentially enable the barrier on systems where the host firmware
  59          * is not updated, but that's harmless as it's a no-op.
  60          */
  61         enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
  62                  security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);
  63
  64         if (!no_nospec && !cpu_mitigations_off())
  65                 enable_barrier_nospec(enable);
  66 }
  67
  68 static int __init handle_nospectre_v1(char *p)
  69 {
  70         no_nospec = true;
  71
  72         return 0;
  73 }
  74 early_param("nospectre_v1", handle_nospectre_v1);
  75
  76 #ifdef CONFIG_DEBUG_FS
  77 static int barrier_nospec_set(void *data, u64 val)
  78 {
  79         switch (val) {
  80         case 0:
  81         case 1:
  82                 break;
  83         default:
  84                 return -EINVAL;
  85         }
  86
  87         if (!!val == !!barrier_nospec_enabled)
  88                 return 0;
  89
  90         enable_barrier_nospec(!!val);
  91
  92         return 0;
  93 }
  94
  95 static int barrier_nospec_get(void *data, u64 *val)
  96 {
  97         *val = barrier_nospec_enabled ? 1 : 0;
  98         return 0;
  99 }
 100
 101 DEFINE_DEBUGFS_ATTRIBUTE(fops_barrier_nospec, barrier_nospec_get,
 102                          barrier_nospec_set, "%llu\n");
 103
 104 static __init int barrier_nospec_debugfs_init(void)
 105 {
 106         debugfs_create_file_unsafe("barrier_nospec", 0600,
 107                                    powerpc_debugfs_root, NULL,
 108                                    &fops_barrier_nospec);
 109         return 0;
 110 }
 111 device_initcall(barrier_nospec_debugfs_init);
 112
 113 static __init int security_feature_debugfs_init(void)
 114 {
 115         debugfs_create_x64("security_features", 0400, powerpc_debugfs_root,
 116                            &powerpc_security_features);
 117         return 0;
 118 }
 119 device_initcall(security_feature_debugfs_init);
 120 #endif /* CONFIG_DEBUG_FS */
 121
 122 #if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
 123 static int __init handle_nospectre_v2(char *p)
 124 {
 125         no_spectrev2 = true;
 126
 127         return 0;
 128 }
 129 early_param("nospectre_v2", handle_nospectre_v2);
 130 #endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */
 131
 132 #ifdef CONFIG_PPC_FSL_BOOK3E
 133 void setup_spectre_v2(void)
 134 {
 135         if (no_spectrev2 || cpu_mitigations_off())
 136                 do_btb_flush_fixups();
 137         else
 138                 btb_flush_enabled = true;
 139 }
 140 #endif /* CONFIG_PPC_FSL_BOOK3E */
 141
 142 #ifdef CONFIG_PPC_BOOK3S_64
 143 ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
 144 {
 145         bool thread_priv;
 146
 147         thread_priv = security_ftr_enabled(SEC_FTR_L1D_THREAD_PRIV);
 148
 149         if (rfi_flush) {
 150                 struct seq_buf s;
 151                 seq_buf_init(&s, buf, PAGE_SIZE - 1);
 152
 153                 seq_buf_printf(&s, "Mitigation: RFI Flush");
 154                 if (thread_priv)
 155                         seq_buf_printf(&s, ", L1D private per thread");
 156
 157                 seq_buf_printf(&s, "\n");
 158
 159                 return s.len;
 160         }
 161
 162         if (thread_priv)
 163                 return sprintf(buf, "Vulnerable: L1D private per thread\n");
 164
 165         if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
 166             !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
 167                 return sprintf(buf, "Not affected\n");
 168
 169         return sprintf(buf, "Vulnerable\n");
 170 }
 171
 172 ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf)
 173 {
 174         return cpu_show_meltdown(dev, attr, buf);
 175 }
 176 #endif
 177
 178 ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf)
 179 {
 180         struct seq_buf s;
 181
 182         seq_buf_init(&s, buf, PAGE_SIZE - 1);
 183
 184         if (security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR)) {
 185                 if (barrier_nospec_enabled)
 186                         seq_buf_printf(&s, "Mitigation: __user pointer sanitization");
 187                 else
 188                         seq_buf_printf(&s, "Vulnerable");
 189
 190                 if (security_ftr_enabled(SEC_FTR_SPEC_BAR_ORI31))
 191                         seq_buf_printf(&s, ", ori31 speculation barrier enabled");
 192
 193                 seq_buf_printf(&s, "\n");
 194         } else
 195                 seq_buf_printf(&s, "Not affected\n");
 196
 197         return s.len;
 198 }
 199
 200 ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
 201 {
 202         struct seq_buf s;
 203         bool bcs, ccd;
 204
 205         seq_buf_init(&s, buf, PAGE_SIZE - 1);
 206
 207         bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
 208         ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
 209
 210         if (bcs || ccd) {
 211                 seq_buf_printf(&s, "Mitigation: ");
 212
 213                 if (bcs)
 214                         seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");
 215
 216                 if (bcs && ccd)
 217                         seq_buf_printf(&s, ", ");
 218
 219                 if (ccd)
 220                         seq_buf_printf(&s, "Indirect branch cache disabled");
 221
 222                 if (link_stack_flush_enabled)
 223                         seq_buf_printf(&s, ", Software link stack flush");
 224
 225         } else if (count_cache_flush_type != COUNT_CACHE_FLUSH_NONE) {
 226                 seq_buf_printf(&s, "Mitigation: Software count cache flush");
 227
 228                 if (count_cache_flush_type == COUNT_CACHE_FLUSH_HW)
 229                         seq_buf_printf(&s, " (hardware accelerated)");
 230
 231                 if (link_stack_flush_enabled)
 232                         seq_buf_printf(&s, ", Software link stack flush");
 233
 234         } else if (btb_flush_enabled) {
 235                 seq_buf_printf(&s, "Mitigation: Branch predictor state flush");
 236         } else {
 237                 seq_buf_printf(&s, "Vulnerable");
 238         }
 239
 240         seq_buf_printf(&s, "\n");
 241
 242         return s.len;
 243 }
 244
 245 #ifdef CONFIG_PPC_BOOK3S_64
 246 /*
 247  * Store-forwarding barrier support.
 248  */
 249
 250 static enum stf_barrier_type stf_enabled_flush_types;
 251 static bool no_stf_barrier;
 252 bool stf_barrier;
 253
 254 static int __init handle_no_stf_barrier(char *p)
 255 {
 256         pr_info("stf-barrier: disabled on command line.");
 257         no_stf_barrier = true;
 258         return 0;
 259 }
 260
 261 early_param("no_stf_barrier", handle_no_stf_barrier);
 262
 263 /* This is the generic flag used by other architectures */
 264 static int __init handle_ssbd(char *p)
 265 {
 266         if (!p || strncmp(p, "auto", 5) == 0 || strncmp(p, "on", 2) == 0 ) {
 267                 /* Until firmware tells us, we have the barrier with auto */
 268                 return 0;
 269         } else if (strncmp(p, "off", 3) == 0) {
 270                 handle_no_stf_barrier(NULL);
 271                 return 0;
 272         } else
 273                 return 1;
 274
 275         return 0;
 276 }
 277 early_param("spec_store_bypass_disable", handle_ssbd);
 278
 279 /* This is the generic flag used by other architectures */
 280 static int __init handle_no_ssbd(char *p)
 281 {
 282         handle_no_stf_barrier(NULL);
 283         return 0;
 284 }
 285 early_param("nospec_store_bypass_disable", handle_no_ssbd);
 286
 287 static void stf_barrier_enable(bool enable)
 288 {
 289         if (enable)
 290                 do_stf_barrier_fixups(stf_enabled_flush_types);
 291         else
 292                 do_stf_barrier_fixups(STF_BARRIER_NONE);
 293
 294         stf_barrier = enable;
 295 }
 296
 297 void setup_stf_barrier(void)
 298 {
 299         enum stf_barrier_type type;
 300         bool enable, hv;
 301
 302         hv = cpu_has_feature(CPU_FTR_HVMODE);
 303
 304         /* Default to fallback in case fw-features are not available */
 305         if (cpu_has_feature(CPU_FTR_ARCH_300))
 306                 type = STF_BARRIER_EIEIO;
 307         else if (cpu_has_feature(CPU_FTR_ARCH_207S))
 308                 type = STF_BARRIER_SYNC_ORI;
 309         else if (cpu_has_feature(CPU_FTR_ARCH_206))
 310                 type = STF_BARRIER_FALLBACK;
 311         else
 312                 type = STF_BARRIER_NONE;
 313
 314         enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
 315                 (security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR) ||
 316                  (security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) && hv));
 317
 318         if (type == STF_BARRIER_FALLBACK) {
 319                 pr_info("stf-barrier: fallback barrier available\n");
 320         } else if (type == STF_BARRIER_SYNC_ORI) {
 321                 pr_info("stf-barrier: hwsync barrier available\n");
 322         } else if (type == STF_BARRIER_EIEIO) {
 323                 pr_info("stf-barrier: eieio barrier available\n");
 324         }
 325
 326         stf_enabled_flush_types = type;
 327
 328         if (!no_stf_barrier && !cpu_mitigations_off())
 329                 stf_barrier_enable(enable);
 330 }
 331
 332 ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
 333 {
 334         if (stf_barrier && stf_enabled_flush_types != STF_BARRIER_NONE) {
 335                 const char *type;
 336                 switch (stf_enabled_flush_types) {
 337                 case STF_BARRIER_EIEIO:
 338                         type = "eieio";
 339                         break;
 340                 case STF_BARRIER_SYNC_ORI:
 341                         type = "hwsync";
 342                         break;
 343                 case STF_BARRIER_FALLBACK:
 344                         type = "fallback";
 345                         break;
 346                 default:
 347                         type = "unknown";
 348                 }
 349                 return sprintf(buf, "Mitigation: Kernel entry/exit barrier (%s)\n", type);
 350         }
 351
 352         if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
 353             !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
 354                 return sprintf(buf, "Not affected\n");
 355
 356         return sprintf(buf, "Vulnerable\n");
 357 }
 358
 359 static int ssb_prctl_get(struct task_struct *task)
 360 {
 361         if (stf_enabled_flush_types == STF_BARRIER_NONE)
 362                 /*
 363                  * We don't have an explicit signal from firmware that we're
 364                  * vulnerable or not, we only have certain CPU revisions that
 365                  * are known to be vulnerable.
 366                  *
 367                  * We assume that if we're on another CPU, where the barrier is
 368                  * NONE, then we are not vulnerable.
 369                  */
 370                 return PR_SPEC_NOT_AFFECTED;
 371         else
 372                 /*
 373                  * If we do have a barrier type then we are vulnerable. The
 374                  * barrier is not a global or per-process mitigation, so the
 375                  * only value we can report here is PR_SPEC_ENABLE, which
 376                  * appears as "vulnerable" in /proc.
 377                  */
 378                 return PR_SPEC_ENABLE;
 379
 380         return -EINVAL;
 381 }
 382
 383 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 384 {
 385         switch (which) {
 386         case PR_SPEC_STORE_BYPASS:
 387                 return ssb_prctl_get(task);
 388         default:
 389                 return -ENODEV;
 390         }
 391 }
 392
 393 #ifdef CONFIG_DEBUG_FS
 394 static int stf_barrier_set(void *data, u64 val)
 395 {
 396         bool enable;
 397
 398         if (val == 1)
 399                 enable = true;
 400         else if (val == 0)
 401                 enable = false;
 402         else
 403                 return -EINVAL;
 404
 405         /* Only do anything if we're changing state */
 406         if (enable != stf_barrier)
 407                 stf_barrier_enable(enable);
 408
 409         return 0;
 410 }
 411
 412 static int stf_barrier_get(void *data, u64 *val)
 413 {
 414         *val = stf_barrier ? 1 : 0;
 415         return 0;
 416 }
 417
 418 DEFINE_DEBUGFS_ATTRIBUTE(fops_stf_barrier, stf_barrier_get, stf_barrier_set,
 419                          "%llu\n");
 420
 421 static __init int stf_barrier_debugfs_init(void)
 422 {
 423         debugfs_create_file_unsafe("stf_barrier", 0600, powerpc_debugfs_root,
 424                                    NULL, &fops_stf_barrier);
 425         return 0;
 426 }
 427 device_initcall(stf_barrier_debugfs_init);
 428 #endif /* CONFIG_DEBUG_FS */
 429
 430 static void no_count_cache_flush(void)
 431 {
 432         count_cache_flush_type = COUNT_CACHE_FLUSH_NONE;
 433         pr_info("count-cache-flush: software flush disabled.\n");
 434 }
 435
 436 static void toggle_count_cache_flush(bool enable)
 437 {
 438         if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE) &&
 439             !security_ftr_enabled(SEC_FTR_FLUSH_LINK_STACK))
 440                 enable = false;
 441
 442         if (!enable) {
 443                 patch_instruction_site(&patch__call_flush_count_cache,
 444                                        ppc_inst(PPC_INST_NOP));
 445 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 446                 patch_instruction_site(&patch__call_kvm_flush_link_stack,
 447                                        ppc_inst(PPC_INST_NOP));
 448 #endif
 449                 pr_info("link-stack-flush: software flush disabled.\n");
 450                 link_stack_flush_enabled = false;
 451                 no_count_cache_flush();
 452                 return;
 453         }
 454
 455         // This enables the branch from _switch to flush_count_cache
 456         patch_branch_site(&patch__call_flush_count_cache,
 457                           (u64)&flush_count_cache, BRANCH_SET_LINK);
 458
 459 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 460         // This enables the branch from guest_exit_cont to kvm_flush_link_stack
 461         patch_branch_site(&patch__call_kvm_flush_link_stack,
 462                           (u64)&kvm_flush_link_stack, BRANCH_SET_LINK);
 463 #endif
 464
 465         pr_info("link-stack-flush: software flush enabled.\n");
 466         link_stack_flush_enabled = true;
 467
 468         // If we just need to flush the link stack, patch an early return
 469         if (!security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE)) {
 470                 patch_instruction_site(&patch__flush_link_stack_return,
 471                                        ppc_inst(PPC_INST_BLR));
 472                 no_count_cache_flush();
 473                 return;
 474         }
 475
 476         if (!security_ftr_enabled(SEC_FTR_BCCTR_FLUSH_ASSIST)) {
 477                 count_cache_flush_type = COUNT_CACHE_FLUSH_SW;
 478                 pr_info("count-cache-flush: full software flush sequence enabled.\n");
 479                 return;
 480         }
 481
 482         patch_instruction_site(&patch__flush_count_cache_return, ppc_inst(PPC_INST_BLR));
 483         count_cache_flush_type = COUNT_CACHE_FLUSH_HW;
 484         pr_info("count-cache-flush: hardware assisted flush sequence enabled\n");
 485 }
 486
 487 void setup_count_cache_flush(void)
 488 {
 489         bool enable = true;
 490
 491         if (no_spectrev2 || cpu_mitigations_off()) {
 492                 if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) ||
 493                     security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED))
 494                         pr_warn("Spectre v2 mitigations not fully under software control, can't disable\n");
 495
 496                 enable = false;
 497         }
 498
 499         /*
 500          * There's no firmware feature flag/hypervisor bit to tell us we need to
 501          * flush the link stack on context switch. So we set it here if we see
 502          * either of the Spectre v2 mitigations that aim to protect userspace.
 503          */
 504         if (security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED) ||
 505             security_ftr_enabled(SEC_FTR_FLUSH_COUNT_CACHE))
 506                 security_ftr_set(SEC_FTR_FLUSH_LINK_STACK);
 507
 508         toggle_count_cache_flush(enable);
 509 }
 510
 511 #ifdef CONFIG_DEBUG_FS
 512 static int count_cache_flush_set(void *data, u64 val)
 513 {
 514         bool enable;
 515
 516         if (val == 1)
 517                 enable = true;
 518         else if (val == 0)
 519                 enable = false;
 520         else
 521                 return -EINVAL;
 522
 523         toggle_count_cache_flush(enable);
 524
 525         return 0;
 526 }
 527
 528 static int count_cache_flush_get(void *data, u64 *val)
 529 {
 530         if (count_cache_flush_type == COUNT_CACHE_FLUSH_NONE)
 531                 *val = 0;
 532         else
 533                 *val = 1;
 534
 535         return 0;
 536 }
 537
 538 DEFINE_DEBUGFS_ATTRIBUTE(fops_count_cache_flush, count_cache_flush_get,
 539                          count_cache_flush_set, "%llu\n");
 540
 541 static __init int count_cache_flush_debugfs_init(void)
 542 {
 543         debugfs_create_file_unsafe("count_cache_flush", 0600,
 544                                    powerpc_debugfs_root, NULL,
 545                                    &fops_count_cache_flush);
 546         return 0;
 547 }
 548 device_initcall(count_cache_flush_debugfs_init);
 549 #endif /* CONFIG_DEBUG_FS */
 550 #endif /* CONFIG_PPC_BOOK3S_64 */