1 // SPDX-License-Identifier: GPL-2.0-only 2 3 #ifndef KVM_X86_MMU_SPTE_H 4 #define KVM_X86_MMU_SPTE_H 5 6 #include "mmu_internal.h" 7 8 /* 9 * A MMU present SPTE is backed by actual memory and may or may not be present 10 * in hardware. E.g. MMIO SPTEs are not considered present. Use bit 11, as it 11 * is ignored by all flavors of SPTEs and checking a low bit often generates 12 * better code than for a high bit, e.g. 56+. MMU present checks are pervasive 13 * enough that the improved code generation is noticeable in KVM's footprint. 14 */ 15 #define SPTE_MMU_PRESENT_MASK BIT_ULL(11) 16 17 /* 18 * TDP SPTES (more specifically, EPT SPTEs) may not have A/D bits, and may also 19 * be restricted to using write-protection (for L2 when CPU dirty logging, i.e. 20 * PML, is enabled). Use bits 52 and 53 to hold the type of A/D tracking that 21 * is must be employed for a given TDP SPTE. 22 * 23 * Note, the "enabled" mask must be '0', as bits 62:52 are _reserved_ for PAE 24 * paging, including NPT PAE. This scheme works because legacy shadow paging 25 * is guaranteed to have A/D bits and write-protection is forced only for 26 * TDP with CPU dirty logging (PML). If NPT ever gains PML-like support, it 27 * must be restricted to 64-bit KVM. 28 */ 29 #define SPTE_TDP_AD_SHIFT 52 30 #define SPTE_TDP_AD_MASK (3ULL << SPTE_TDP_AD_SHIFT) 31 #define SPTE_TDP_AD_ENABLED_MASK (0ULL << SPTE_TDP_AD_SHIFT) 32 #define SPTE_TDP_AD_DISABLED_MASK (1ULL << SPTE_TDP_AD_SHIFT) 33 #define SPTE_TDP_AD_WRPROT_ONLY_MASK (2ULL << SPTE_TDP_AD_SHIFT) 34 static_assert(SPTE_TDP_AD_ENABLED_MASK == 0); 35 36 #ifdef CONFIG_DYNAMIC_PHYSICAL_MASK 37 #define SPTE_BASE_ADDR_MASK (physical_mask & ~(u64)(PAGE_SIZE-1)) 38 #else 39 #define SPTE_BASE_ADDR_MASK (((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1)) 40 #endif 41 42 #define SPTE_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | shadow_user_mask \ 43 | shadow_x_mask | shadow_nx_mask | shadow_me_mask) 44 45 #define ACC_EXEC_MASK 1 46 #define ACC_WRITE_MASK PT_WRITABLE_MASK 47 #define ACC_USER_MASK PT_USER_MASK 48 #define ACC_ALL (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK) 49 50 /* The mask for the R/X bits in EPT PTEs */ 51 #define SPTE_EPT_READABLE_MASK 0x1ull 52 #define SPTE_EPT_EXECUTABLE_MASK 0x4ull 53 54 #define SPTE_LEVEL_BITS 9 55 #define SPTE_LEVEL_SHIFT(level) __PT_LEVEL_SHIFT(level, SPTE_LEVEL_BITS) 56 #define SPTE_INDEX(address, level) __PT_INDEX(address, level, SPTE_LEVEL_BITS) 57 #define SPTE_ENT_PER_PAGE __PT_ENT_PER_PAGE(SPTE_LEVEL_BITS) 58 59 /* 60 * The mask/shift to use for saving the original R/X bits when marking the PTE 61 * as not-present for access tracking purposes. We do not save the W bit as the 62 * PTEs being access tracked also need to be dirty tracked, so the W bit will be 63 * restored only when a write is attempted to the page. This mask obviously 64 * must not overlap the A/D type mask. 65 */ 66 #define SHADOW_ACC_TRACK_SAVED_BITS_MASK (SPTE_EPT_READABLE_MASK | \ 67 SPTE_EPT_EXECUTABLE_MASK) 68 #define SHADOW_ACC_TRACK_SAVED_BITS_SHIFT 54 69 #define SHADOW_ACC_TRACK_SAVED_MASK (SHADOW_ACC_TRACK_SAVED_BITS_MASK << \ 70 SHADOW_ACC_TRACK_SAVED_BITS_SHIFT) 71 static_assert(!(SPTE_TDP_AD_MASK & SHADOW_ACC_TRACK_SAVED_MASK)); 72 73 /* 74 * {DEFAULT,EPT}_SPTE_{HOST,MMU}_WRITABLE are used to keep track of why a given 75 * SPTE is write-protected. See is_writable_pte() for details. 76 */ 77 78 /* Bits 9 and 10 are ignored by all non-EPT PTEs. */ 79 #define DEFAULT_SPTE_HOST_WRITABLE BIT_ULL(9) 80 #define DEFAULT_SPTE_MMU_WRITABLE BIT_ULL(10) 81 82 /* 83 * Low ignored bits are at a premium for EPT, use high ignored bits, taking care 84 * to not overlap the A/D type mask or the saved access bits of access-tracked 85 * SPTEs when A/D bits are disabled. 86 */ 87 #define EPT_SPTE_HOST_WRITABLE BIT_ULL(57) 88 #define EPT_SPTE_MMU_WRITABLE BIT_ULL(58) 89 90 static_assert(!(EPT_SPTE_HOST_WRITABLE & SPTE_TDP_AD_MASK)); 91 static_assert(!(EPT_SPTE_MMU_WRITABLE & SPTE_TDP_AD_MASK)); 92 static_assert(!(EPT_SPTE_HOST_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK)); 93 static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK)); 94 95 /* Defined only to keep the above static asserts readable. */ 96 #undef SHADOW_ACC_TRACK_SAVED_MASK 97 98 /* 99 * Due to limited space in PTEs, the MMIO generation is a 19 bit subset of 100 * the memslots generation and is derived as follows: 101 * 102 * Bits 0-7 of the MMIO generation are propagated to spte bits 3-10 103 * Bits 8-18 of the MMIO generation are propagated to spte bits 52-62 104 * 105 * The KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag is intentionally not included in 106 * the MMIO generation number, as doing so would require stealing a bit from 107 * the "real" generation number and thus effectively halve the maximum number 108 * of MMIO generations that can be handled before encountering a wrap (which 109 * requires a full MMU zap). The flag is instead explicitly queried when 110 * checking for MMIO spte cache hits. 111 */ 112 113 #define MMIO_SPTE_GEN_LOW_START 3 114 #define MMIO_SPTE_GEN_LOW_END 10 115 116 #define MMIO_SPTE_GEN_HIGH_START 52 117 #define MMIO_SPTE_GEN_HIGH_END 62 118 119 #define MMIO_SPTE_GEN_LOW_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \ 120 MMIO_SPTE_GEN_LOW_START) 121 #define MMIO_SPTE_GEN_HIGH_MASK GENMASK_ULL(MMIO_SPTE_GEN_HIGH_END, \ 122 MMIO_SPTE_GEN_HIGH_START) 123 static_assert(!(SPTE_MMU_PRESENT_MASK & 124 (MMIO_SPTE_GEN_LOW_MASK | MMIO_SPTE_GEN_HIGH_MASK))); 125 126 /* 127 * The SPTE MMIO mask must NOT overlap the MMIO generation bits or the 128 * MMU-present bit. The generation obviously co-exists with the magic MMIO 129 * mask/value, and MMIO SPTEs are considered !MMU-present. 130 * 131 * The SPTE MMIO mask is allowed to use hardware "present" bits (i.e. all EPT 132 * RWX bits), all physical address bits (legal PA bits are used for "fast" MMIO 133 * and so they're off-limits for generation; additional checks ensure the mask 134 * doesn't overlap legal PA bits), and bit 63 (carved out for future usage). 135 */ 136 #define SPTE_MMIO_ALLOWED_MASK (BIT_ULL(63) | GENMASK_ULL(51, 12) | GENMASK_ULL(2, 0)) 137 static_assert(!(SPTE_MMIO_ALLOWED_MASK & 138 (SPTE_MMU_PRESENT_MASK | MMIO_SPTE_GEN_LOW_MASK | MMIO_SPTE_GEN_HIGH_MASK))); 139 140 #define MMIO_SPTE_GEN_LOW_BITS (MMIO_SPTE_GEN_LOW_END - MMIO_SPTE_GEN_LOW_START + 1) 141 #define MMIO_SPTE_GEN_HIGH_BITS (MMIO_SPTE_GEN_HIGH_END - MMIO_SPTE_GEN_HIGH_START + 1) 142 143 /* remember to adjust the comment above as well if you change these */ 144 static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11); 145 146 #define MMIO_SPTE_GEN_LOW_SHIFT (MMIO_SPTE_GEN_LOW_START - 0) 147 #define MMIO_SPTE_GEN_HIGH_SHIFT (MMIO_SPTE_GEN_HIGH_START - MMIO_SPTE_GEN_LOW_BITS) 148 149 #define MMIO_SPTE_GEN_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0) 150 151 extern u64 __read_mostly shadow_host_writable_mask; 152 extern u64 __read_mostly shadow_mmu_writable_mask; 153 extern u64 __read_mostly shadow_nx_mask; 154 extern u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */ 155 extern u64 __read_mostly shadow_user_mask; 156 extern u64 __read_mostly shadow_accessed_mask; 157 extern u64 __read_mostly shadow_dirty_mask; 158 extern u64 __read_mostly shadow_mmio_value; 159 extern u64 __read_mostly shadow_mmio_mask; 160 extern u64 __read_mostly shadow_mmio_access_mask; 161 extern u64 __read_mostly shadow_present_mask; 162 extern u64 __read_mostly shadow_memtype_mask; 163 extern u64 __read_mostly shadow_me_value; 164 extern u64 __read_mostly shadow_me_mask; 165 166 /* 167 * SPTEs in MMUs without A/D bits are marked with SPTE_TDP_AD_DISABLED_MASK; 168 * shadow_acc_track_mask is the set of bits to be cleared in non-accessed 169 * pages. 170 */ 171 extern u64 __read_mostly shadow_acc_track_mask; 172 173 /* 174 * This mask must be set on all non-zero Non-Present or Reserved SPTEs in order 175 * to guard against L1TF attacks. 176 */ 177 extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask; 178 179 /* 180 * The number of high-order 1 bits to use in the mask above. 181 */ 182 #define SHADOW_NONPRESENT_OR_RSVD_MASK_LEN 5 183 184 /* 185 * If a thread running without exclusive control of the MMU lock must perform a 186 * multi-part operation on an SPTE, it can set the SPTE to REMOVED_SPTE as a 187 * non-present intermediate value. Other threads which encounter this value 188 * should not modify the SPTE. 189 * 190 * Use a semi-arbitrary value that doesn't set RWX bits, i.e. is not-present on 191 * bot AMD and Intel CPUs, and doesn't set PFN bits, i.e. doesn't create a L1TF 192 * vulnerability. Use only low bits to avoid 64-bit immediates. 193 * 194 * Only used by the TDP MMU. 195 */ 196 #define REMOVED_SPTE 0x5a0ULL 197 198 /* Removed SPTEs must not be misconstrued as shadow present PTEs. */ 199 static_assert(!(REMOVED_SPTE & SPTE_MMU_PRESENT_MASK)); 200 201 static inline bool is_removed_spte(u64 spte) 202 { 203 return spte == REMOVED_SPTE; 204 } 205 206 /* Get an SPTE's index into its parent's page table (and the spt array). */ 207 static inline int spte_index(u64 *sptep) 208 { 209 return ((unsigned long)sptep / sizeof(*sptep)) & (SPTE_ENT_PER_PAGE - 1); 210 } 211 212 /* 213 * In some cases, we need to preserve the GFN of a non-present or reserved 214 * SPTE when we usurp the upper five bits of the physical address space to 215 * defend against L1TF, e.g. for MMIO SPTEs. To preserve the GFN, we'll 216 * shift bits of the GFN that overlap with shadow_nonpresent_or_rsvd_mask 217 * left into the reserved bits, i.e. the GFN in the SPTE will be split into 218 * high and low parts. This mask covers the lower bits of the GFN. 219 */ 220 extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask; 221 222 static inline bool is_mmio_spte(u64 spte) 223 { 224 return (spte & shadow_mmio_mask) == shadow_mmio_value && 225 likely(enable_mmio_caching); 226 } 227 228 static inline bool is_shadow_present_pte(u64 pte) 229 { 230 return !!(pte & SPTE_MMU_PRESENT_MASK); 231 } 232 233 /* 234 * Returns true if A/D bits are supported in hardware and are enabled by KVM. 235 * When enabled, KVM uses A/D bits for all non-nested MMUs. Because L1 can 236 * disable A/D bits in EPTP12, SP and SPTE variants are needed to handle the 237 * scenario where KVM is using A/D bits for L1, but not L2. 238 */ 239 static inline bool kvm_ad_enabled(void) 240 { 241 return !!shadow_accessed_mask; 242 } 243 244 static inline bool sp_ad_disabled(struct kvm_mmu_page *sp) 245 { 246 return sp->role.ad_disabled; 247 } 248 249 static inline bool spte_ad_enabled(u64 spte) 250 { 251 MMU_WARN_ON(!is_shadow_present_pte(spte)); 252 return (spte & SPTE_TDP_AD_MASK) != SPTE_TDP_AD_DISABLED_MASK; 253 } 254 255 static inline bool spte_ad_need_write_protect(u64 spte) 256 { 257 MMU_WARN_ON(!is_shadow_present_pte(spte)); 258 /* 259 * This is benign for non-TDP SPTEs as SPTE_TDP_AD_ENABLED_MASK is '0', 260 * and non-TDP SPTEs will never set these bits. Optimize for 64-bit 261 * TDP and do the A/D type check unconditionally. 262 */ 263 return (spte & SPTE_TDP_AD_MASK) != SPTE_TDP_AD_ENABLED_MASK; 264 } 265 266 static inline u64 spte_shadow_accessed_mask(u64 spte) 267 { 268 MMU_WARN_ON(!is_shadow_present_pte(spte)); 269 return spte_ad_enabled(spte) ? shadow_accessed_mask : 0; 270 } 271 272 static inline u64 spte_shadow_dirty_mask(u64 spte) 273 { 274 MMU_WARN_ON(!is_shadow_present_pte(spte)); 275 return spte_ad_enabled(spte) ? shadow_dirty_mask : 0; 276 } 277 278 static inline bool is_access_track_spte(u64 spte) 279 { 280 return !spte_ad_enabled(spte) && (spte & shadow_acc_track_mask) == 0; 281 } 282 283 static inline bool is_large_pte(u64 pte) 284 { 285 return pte & PT_PAGE_SIZE_MASK; 286 } 287 288 static inline bool is_last_spte(u64 pte, int level) 289 { 290 return (level == PG_LEVEL_4K) || is_large_pte(pte); 291 } 292 293 static inline bool is_executable_pte(u64 spte) 294 { 295 return (spte & (shadow_x_mask | shadow_nx_mask)) == shadow_x_mask; 296 } 297 298 static inline kvm_pfn_t spte_to_pfn(u64 pte) 299 { 300 return (pte & SPTE_BASE_ADDR_MASK) >> PAGE_SHIFT; 301 } 302 303 static inline bool is_accessed_spte(u64 spte) 304 { 305 u64 accessed_mask = spte_shadow_accessed_mask(spte); 306 307 return accessed_mask ? spte & accessed_mask 308 : !is_access_track_spte(spte); 309 } 310 311 static inline bool is_dirty_spte(u64 spte) 312 { 313 u64 dirty_mask = spte_shadow_dirty_mask(spte); 314 315 return dirty_mask ? spte & dirty_mask : spte & PT_WRITABLE_MASK; 316 } 317 318 static inline u64 get_rsvd_bits(struct rsvd_bits_validate *rsvd_check, u64 pte, 319 int level) 320 { 321 int bit7 = (pte >> 7) & 1; 322 323 return rsvd_check->rsvd_bits_mask[bit7][level-1]; 324 } 325 326 static inline bool __is_rsvd_bits_set(struct rsvd_bits_validate *rsvd_check, 327 u64 pte, int level) 328 { 329 return pte & get_rsvd_bits(rsvd_check, pte, level); 330 } 331 332 static inline bool __is_bad_mt_xwr(struct rsvd_bits_validate *rsvd_check, 333 u64 pte) 334 { 335 return rsvd_check->bad_mt_xwr & BIT_ULL(pte & 0x3f); 336 } 337 338 static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check, 339 u64 spte, int level) 340 { 341 return __is_bad_mt_xwr(rsvd_check, spte) || 342 __is_rsvd_bits_set(rsvd_check, spte, level); 343 } 344 345 /* 346 * A shadow-present leaf SPTE may be non-writable for 4 possible reasons: 347 * 348 * 1. To intercept writes for dirty logging. KVM write-protects huge pages 349 * so that they can be split be split down into the dirty logging 350 * granularity (4KiB) whenever the guest writes to them. KVM also 351 * write-protects 4KiB pages so that writes can be recorded in the dirty log 352 * (e.g. if not using PML). SPTEs are write-protected for dirty logging 353 * during the VM-iotcls that enable dirty logging. 354 * 355 * 2. To intercept writes to guest page tables that KVM is shadowing. When a 356 * guest writes to its page table the corresponding shadow page table will 357 * be marked "unsync". That way KVM knows which shadow page tables need to 358 * be updated on the next TLB flush, INVLPG, etc. and which do not. 359 * 360 * 3. To prevent guest writes to read-only memory, such as for memory in a 361 * read-only memslot or guest memory backed by a read-only VMA. Writes to 362 * such pages are disallowed entirely. 363 * 364 * 4. To emulate the Accessed bit for SPTEs without A/D bits. Note, in this 365 * case, the SPTE is access-protected, not just write-protected! 366 * 367 * For cases #1 and #4, KVM can safely make such SPTEs writable without taking 368 * mmu_lock as capturing the Accessed/Dirty state doesn't require taking it. 369 * To differentiate #1 and #4 from #2 and #3, KVM uses two software-only bits 370 * in the SPTE: 371 * 372 * shadow_mmu_writable_mask, aka MMU-writable - 373 * Cleared on SPTEs that KVM is currently write-protecting for shadow paging 374 * purposes (case 2 above). 375 * 376 * shadow_host_writable_mask, aka Host-writable - 377 * Cleared on SPTEs that are not host-writable (case 3 above) 378 * 379 * Note, not all possible combinations of PT_WRITABLE_MASK, 380 * shadow_mmu_writable_mask, and shadow_host_writable_mask are valid. A given 381 * SPTE can be in only one of the following states, which map to the 382 * aforementioned 3 cases: 383 * 384 * shadow_host_writable_mask | shadow_mmu_writable_mask | PT_WRITABLE_MASK 385 * ------------------------- | ------------------------ | ---------------- 386 * 1 | 1 | 1 (writable) 387 * 1 | 1 | 0 (case 1) 388 * 1 | 0 | 0 (case 2) 389 * 0 | 0 | 0 (case 3) 390 * 391 * The valid combinations of these bits are checked by 392 * check_spte_writable_invariants() whenever an SPTE is modified. 393 * 394 * Clearing the MMU-writable bit is always done under the MMU lock and always 395 * accompanied by a TLB flush before dropping the lock to avoid corrupting the 396 * shadow page tables between vCPUs. Write-protecting an SPTE for dirty logging 397 * (which does not clear the MMU-writable bit), does not flush TLBs before 398 * dropping the lock, as it only needs to synchronize guest writes with the 399 * dirty bitmap. Similarly, making the SPTE inaccessible (and non-writable) for 400 * access-tracking via the clear_young() MMU notifier also does not flush TLBs. 401 * 402 * So, there is the problem: clearing the MMU-writable bit can encounter a 403 * write-protected SPTE while CPUs still have writable mappings for that SPTE 404 * cached in their TLB. To address this, KVM always flushes TLBs when 405 * write-protecting SPTEs if the MMU-writable bit is set on the old SPTE. 406 * 407 * The Host-writable bit is not modified on present SPTEs, it is only set or 408 * cleared when an SPTE is first faulted in from non-present and then remains 409 * immutable. 410 */ 411 static inline bool is_writable_pte(unsigned long pte) 412 { 413 return pte & PT_WRITABLE_MASK; 414 } 415 416 /* Note: spte must be a shadow-present leaf SPTE. */ 417 static inline void check_spte_writable_invariants(u64 spte) 418 { 419 if (spte & shadow_mmu_writable_mask) 420 WARN_ONCE(!(spte & shadow_host_writable_mask), 421 "kvm: MMU-writable SPTE is not Host-writable: %llx", 422 spte); 423 else 424 WARN_ONCE(is_writable_pte(spte), 425 "kvm: Writable SPTE is not MMU-writable: %llx", spte); 426 } 427 428 static inline bool is_mmu_writable_spte(u64 spte) 429 { 430 return spte & shadow_mmu_writable_mask; 431 } 432 433 static inline u64 get_mmio_spte_generation(u64 spte) 434 { 435 u64 gen; 436 437 gen = (spte & MMIO_SPTE_GEN_LOW_MASK) >> MMIO_SPTE_GEN_LOW_SHIFT; 438 gen |= (spte & MMIO_SPTE_GEN_HIGH_MASK) >> MMIO_SPTE_GEN_HIGH_SHIFT; 439 return gen; 440 } 441 442 bool spte_has_volatile_bits(u64 spte); 443 444 bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, 445 const struct kvm_memory_slot *slot, 446 unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn, 447 u64 old_spte, bool prefetch, bool can_unsync, 448 bool host_writable, u64 *new_spte); 449 u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, 450 union kvm_mmu_page_role role, int index); 451 u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled); 452 u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access); 453 u64 mark_spte_for_access_track(u64 spte); 454 455 /* Restore an acc-track PTE back to a regular PTE */ 456 static inline u64 restore_acc_track_spte(u64 spte) 457 { 458 u64 saved_bits = (spte >> SHADOW_ACC_TRACK_SAVED_BITS_SHIFT) 459 & SHADOW_ACC_TRACK_SAVED_BITS_MASK; 460 461 spte &= ~shadow_acc_track_mask; 462 spte &= ~(SHADOW_ACC_TRACK_SAVED_BITS_MASK << 463 SHADOW_ACC_TRACK_SAVED_BITS_SHIFT); 464 spte |= saved_bits; 465 466 return spte; 467 } 468 469 u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn); 470 471 void __init kvm_mmu_spte_module_init(void); 472 void kvm_mmu_reset_all_pte_masks(void); 473 474 #endif 475