compiler/rustc_mir_transform/src/check_unsafety.rs

   1 use rustc_data_structures::fx::FxHashSet;
   2 use rustc_errors::struct_span_err;
   3 use rustc_hir as hir;
   4 use rustc_hir::def_id::{DefId, LocalDefId};
   5 use rustc_hir::hir_id::HirId;
   6 use rustc_hir::intravisit;
   7 use rustc_hir::Node;
   8 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   9 use rustc_middle::mir::*;
  10 use rustc_middle::ty::query::Providers;
  11 use rustc_middle::ty::{self, TyCtxt};
  12 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  13 use rustc_session::lint::Level;
  14
  15 use std::ops::Bound;
  16
  17 pub struct UnsafetyChecker<'a, 'tcx> {
  18     body: &'a Body<'tcx>,
  19     body_did: LocalDefId,
  20     violations: Vec<UnsafetyViolation>,
  21     source_info: SourceInfo,
  22     tcx: TyCtxt<'tcx>,
  23     param_env: ty::ParamEnv<'tcx>,
  24     /// Mark an `unsafe` block as used, so we don't lint it.
  25     used_unsafe: FxHashSet<hir::HirId>,
  26     inherited_blocks: Vec<(hir::HirId, bool)>,
  27 }
  28
  29 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  30     fn new(
  31         body: &'a Body<'tcx>,
  32         body_did: LocalDefId,
  33         tcx: TyCtxt<'tcx>,
  34         param_env: ty::ParamEnv<'tcx>,
  35     ) -> Self {
  36         Self {
  37             body,
  38             body_did,
  39             violations: vec![],
  40             source_info: SourceInfo::outermost(body.span),
  41             tcx,
  42             param_env,
  43             used_unsafe: Default::default(),
  44             inherited_blocks: vec![],
  45         }
  46     }
  47 }
  48
  49 impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
  50     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  51         self.source_info = terminator.source_info;
  52         match terminator.kind {
  53             TerminatorKind::Goto { .. }
  54             | TerminatorKind::SwitchInt { .. }
  55             | TerminatorKind::Drop { .. }
  56             | TerminatorKind::Yield { .. }
  57             | TerminatorKind::Assert { .. }
  58             | TerminatorKind::DropAndReplace { .. }
  59             | TerminatorKind::GeneratorDrop
  60             | TerminatorKind::Resume
  61             | TerminatorKind::Abort
  62             | TerminatorKind::Return
  63             | TerminatorKind::Unreachable
  64             | TerminatorKind::FalseEdge { .. }
  65             | TerminatorKind::FalseUnwind { .. } => {
  66                 // safe (at least as emitted during MIR construction)
  67             }
  68
  69             TerminatorKind::Call { ref func, .. } => {
  70                 let func_ty = func.ty(self.body, self.tcx);
  71                 let sig = func_ty.fn_sig(self.tcx);
  72                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  73                     self.require_unsafe(
  74                         UnsafetyViolationKind::General,
  75                         UnsafetyViolationDetails::CallToUnsafeFunction,
  76                     )
  77                 }
  78
  79                 if let ty::FnDef(func_id, _) = func_ty.kind() {
  80                     self.check_target_features(*func_id);
  81                 }
  82             }
  83
  84             TerminatorKind::InlineAsm { .. } => self.require_unsafe(
  85                 UnsafetyViolationKind::General,
  86                 UnsafetyViolationDetails::UseOfInlineAssembly,
  87             ),
  88         }
  89         self.super_terminator(terminator, location);
  90     }
  91
  92     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  93         self.source_info = statement.source_info;
  94         match statement.kind {
  95             StatementKind::Assign(..)
  96             | StatementKind::FakeRead(..)
  97             | StatementKind::SetDiscriminant { .. }
  98             | StatementKind::StorageLive(..)
  99             | StatementKind::StorageDead(..)
 100             | StatementKind::Retag { .. }
 101             | StatementKind::AscribeUserType(..)
 102             | StatementKind::Coverage(..)
 103             | StatementKind::Nop => {
 104                 // safe (at least as emitted during MIR construction)
 105             }
 106
 107             StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
 108                 UnsafetyViolationKind::General,
 109                 UnsafetyViolationDetails::UseOfInlineAssembly,
 110             ),
 111             StatementKind::CopyNonOverlapping(..) => unreachable!(),
 112         }
 113         self.super_statement(statement, location);
 114     }
 115
 116     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 117         match rvalue {
 118             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 119                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 120                 &AggregateKind::Adt(adt_did, ..) => {
 121                     match self.tcx.layout_scalar_valid_range(adt_did) {
 122                         (Bound::Unbounded, Bound::Unbounded) => {}
 123                         _ => self.require_unsafe(
 124                             UnsafetyViolationKind::General,
 125                             UnsafetyViolationDetails::InitializingTypeWith,
 126                         ),
 127                     }
 128                 }
 129                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 130                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 131                         self.tcx.unsafety_check_result(def_id.expect_local());
 132                     self.register_violations(&violations, &unsafe_blocks);
 133                 }
 134             },
 135             _ => {}
 136         }
 137         self.super_rvalue(rvalue, location);
 138     }
 139
 140     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 141         // On types with `scalar_valid_range`, prevent
 142         // * `&mut x.field`
 143         // * `x.field = y;`
 144         // * `&x.field` if `field`'s type has interior mutability
 145         // because either of these would allow modifying the layout constrained field and
 146         // insert values that violate the layout constraints.
 147         if context.is_mutating_use() || context.is_borrow() {
 148             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 149         }
 150
 151         // Some checks below need the extra metainfo of the local declaration.
 152         let decl = &self.body.local_decls[place.local];
 153
 154         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 155         // temporary holding the static pointer to avoid duplicate errors
 156         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 157         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 158             // If the projection root is an artifical local that we introduced when
 159             // desugaring `static`, give a more specific error message
 160             // (avoid the general "raw pointer" clause below, that would only be confusing).
 161             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 162                 if self.tcx.is_mutable_static(def_id) {
 163                     self.require_unsafe(
 164                         UnsafetyViolationKind::General,
 165                         UnsafetyViolationDetails::UseOfMutableStatic,
 166                     );
 167                     return;
 168                 } else if self.tcx.is_foreign_item(def_id) {
 169                     self.require_unsafe(
 170                         UnsafetyViolationKind::General,
 171                         UnsafetyViolationDetails::UseOfExternStatic,
 172                     );
 173                     return;
 174                 }
 175             }
 176         }
 177
 178         // Check for raw pointer `Deref`.
 179         for (base, proj) in place.iter_projections() {
 180             if proj == ProjectionElem::Deref {
 181                 let base_ty = base.ty(self.body, self.tcx).ty;
 182                 if base_ty.is_unsafe_ptr() {
 183                     self.require_unsafe(
 184                         UnsafetyViolationKind::General,
 185                         UnsafetyViolationDetails::DerefOfRawPointer,
 186                     )
 187                 }
 188             }
 189         }
 190
 191         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 192         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 193         let mut saw_deref = false;
 194         for (base, proj) in place.iter_projections().rev() {
 195             if proj == ProjectionElem::Deref {
 196                 saw_deref = true;
 197                 continue;
 198             }
 199
 200             let base_ty = base.ty(self.body, self.tcx).ty;
 201             if base_ty.is_union() {
 202                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 203                 // rules are different.
 204                 let assign_to_field = !saw_deref
 205                     && matches!(
 206                         context,
 207                         PlaceContext::MutatingUse(
 208                             MutatingUseContext::Store
 209                                 | MutatingUseContext::Drop
 210                                 | MutatingUseContext::AsmOutput
 211                                 | MutatingUseContext::LlvmAsmOutput
 212                         )
 213                     );
 214                 // If this is just an assignment, determine if the assigned type needs dropping.
 215                 if assign_to_field {
 216                     // We have to check the actual type of the assignment, as that determines if the
 217                     // old value is being dropped.
 218                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 219                     // To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
 220                     let manually_drop = assigned_ty
 221                         .ty_adt_def()
 222                         .map_or(false, |adt_def| adt_def.is_manually_drop());
 223                     let nodrop = manually_drop
 224                         || assigned_ty.is_copy_modulo_regions(
 225                             self.tcx.at(self.source_info.span),
 226                             self.param_env,
 227                         );
 228                     if !nodrop {
 229                         self.require_unsafe(
 230                             UnsafetyViolationKind::General,
 231                             UnsafetyViolationDetails::AssignToDroppingUnionField,
 232                         );
 233                     } else {
 234                         // write to non-drop union field, safe
 235                     }
 236                 } else {
 237                     self.require_unsafe(
 238                         UnsafetyViolationKind::General,
 239                         UnsafetyViolationDetails::AccessToUnionField,
 240                     )
 241                 }
 242             }
 243         }
 244     }
 245 }
 246
 247 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 248     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 249         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 250         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 251
 252         let source_info = self.source_info;
 253         let lint_root = self.body.source_scopes[self.source_info.scope]
 254             .local_data
 255             .as_ref()
 256             .assert_crate_local()
 257             .lint_root;
 258         self.register_violations(
 259             &[UnsafetyViolation { source_info, lint_root, kind, details }],
 260             &[],
 261         );
 262     }
 263
 264     fn register_violations(
 265         &mut self,
 266         violations: &[UnsafetyViolation],
 267         unsafe_blocks: &[(hir::HirId, bool)],
 268     ) {
 269         let safety = self.body.source_scopes[self.source_info.scope]
 270             .local_data
 271             .as_ref()
 272             .assert_crate_local()
 273             .safety;
 274         let within_unsafe = match safety {
 275             // `unsafe` blocks are required in safe code
 276             Safety::Safe => {
 277                 for violation in violations {
 278                     match violation.kind {
 279                         UnsafetyViolationKind::General => {}
 280                         UnsafetyViolationKind::UnsafeFn => {
 281                             bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 282                         }
 283                     }
 284                     if !self.violations.contains(violation) {
 285                         self.violations.push(*violation)
 286                     }
 287                 }
 288                 false
 289             }
 290             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 291             Safety::FnUnsafe => {
 292                 for violation in violations {
 293                     let mut violation = *violation;
 294
 295                     violation.kind = UnsafetyViolationKind::UnsafeFn;
 296                     if !self.violations.contains(&violation) {
 297                         self.violations.push(violation)
 298                     }
 299                 }
 300                 false
 301             }
 302             Safety::BuiltinUnsafe => true,
 303             Safety::ExplicitUnsafe(hir_id) => {
 304                 // mark unsafe block as used if there are any unsafe operations inside
 305                 if !violations.is_empty() {
 306                     self.used_unsafe.insert(hir_id);
 307                 }
 308                 true
 309             }
 310         };
 311         self.inherited_blocks.extend(
 312             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 313         );
 314     }
 315     fn check_mut_borrowing_layout_constrained_field(
 316         &mut self,
 317         place: Place<'tcx>,
 318         is_mut_use: bool,
 319     ) {
 320         for (place_base, elem) in place.iter_projections().rev() {
 321             match elem {
 322                 // Modifications behind a dereference don't affect the value of
 323                 // the pointer.
 324                 ProjectionElem::Deref => return,
 325                 ProjectionElem::Field(..) => {
 326                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 327                     if let ty::Adt(def, _) = ty.kind() {
 328                         if self.tcx.layout_scalar_valid_range(def.did)
 329                             != (Bound::Unbounded, Bound::Unbounded)
 330                         {
 331                             let details = if is_mut_use {
 332                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 333
 334                             // Check `is_freeze` as late as possible to avoid cycle errors
 335                             // with opaque types.
 336                             } else if !place
 337                                 .ty(self.body, self.tcx)
 338                                 .ty
 339                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 340                             {
 341                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 342                             } else {
 343                                 continue;
 344                             };
 345                             self.require_unsafe(UnsafetyViolationKind::General, details);
 346                         }
 347                     }
 348                 }
 349                 _ => {}
 350             }
 351         }
 352     }
 353
 354     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 355     /// the called function has target features the calling function hasn't.
 356     fn check_target_features(&mut self, func_did: DefId) {
 357         // Unsafety isn't required on wasm targets. For more information see
 358         // the corresponding check in typeck/src/collect.rs
 359         if self.tcx.sess.target.options.is_like_wasm {
 360             return;
 361         }
 362
 363         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 364         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 365
 366         // Is `callee_features` a subset of `calling_features`?
 367         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 368             self.require_unsafe(
 369                 UnsafetyViolationKind::General,
 370                 UnsafetyViolationDetails::CallToFunctionWith,
 371             )
 372         }
 373     }
 374 }
 375
 376 pub(crate) fn provide(providers: &mut Providers) {
 377     *providers = Providers {
 378         unsafety_check_result: |tcx, def_id| {
 379             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 380                 tcx.unsafety_check_result_for_const_arg(def)
 381             } else {
 382                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 383             }
 384         },
 385         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 386             unsafety_check_result(
 387                 tcx,
 388                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 389             )
 390         },
 391         ..*providers
 392     };
 393 }
 394
 395 struct UnusedUnsafeVisitor<'a> {
 396     used_unsafe: &'a FxHashSet<hir::HirId>,
 397     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 398 }
 399
 400 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_> {
 401     type Map = intravisit::ErasedMap<'tcx>;
 402
 403     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 404         intravisit::NestedVisitorMap::None
 405     }
 406
 407     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 408         intravisit::walk_block(self, block);
 409
 410         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 411             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 412         }
 413     }
 414 }
 415
 416 fn check_unused_unsafe(
 417     tcx: TyCtxt<'_>,
 418     def_id: LocalDefId,
 419     used_unsafe: &FxHashSet<hir::HirId>,
 420     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 421 ) {
 422     let body_id = tcx.hir().maybe_body_owned_by(tcx.hir().local_def_id_to_hir_id(def_id));
 423
 424     let body_id = match body_id {
 425         Some(body) => body,
 426         None => {
 427             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 428             return;
 429         }
 430     };
 431     let body = tcx.hir().body(body_id);
 432     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 433
 434     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 435     intravisit::Visitor::visit_body(&mut visitor, body);
 436 }
 437
 438 fn unsafety_check_result<'tcx>(
 439     tcx: TyCtxt<'tcx>,
 440     def: ty::WithOptConstParam<LocalDefId>,
 441 ) -> &'tcx UnsafetyCheckResult {
 442     debug!("unsafety_violations({:?})", def);
 443
 444     // N.B., this borrow is valid because all the consumers of
 445     // `mir_built` force this.
 446     let body = &tcx.mir_built(def).borrow();
 447
 448     let param_env = tcx.param_env(def.did);
 449
 450     let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
 451     checker.visit_body(&body);
 452
 453     check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
 454
 455     tcx.arena.alloc(UnsafetyCheckResult {
 456         violations: checker.violations.into(),
 457         unsafe_blocks: checker.inherited_blocks.into(),
 458     })
 459 }
 460
 461 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 462 fn is_enclosed(
 463     tcx: TyCtxt<'_>,
 464     used_unsafe: &FxHashSet<hir::HirId>,
 465     id: hir::HirId,
 466     unsafe_op_in_unsafe_fn_allowed: bool,
 467 ) -> Option<(&'static str, hir::HirId)> {
 468     let parent_id = tcx.hir().get_parent_node(id);
 469     if parent_id != id {
 470         if used_unsafe.contains(&parent_id) {
 471             Some(("block", parent_id))
 472         } else if let Some(Node::Item(&hir::Item {
 473             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 474         })) = tcx.hir().find(parent_id)
 475         {
 476             if sig.header.unsafety == hir::Unsafety::Unsafe && unsafe_op_in_unsafe_fn_allowed {
 477                 Some(("fn", parent_id))
 478             } else {
 479                 None
 480             }
 481         } else {
 482             is_enclosed(tcx, used_unsafe, parent_id, unsafe_op_in_unsafe_fn_allowed)
 483         }
 484     } else {
 485         None
 486     }
 487 }
 488
 489 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 490     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 491     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 492         let msg = "unnecessary `unsafe` block";
 493         let mut db = lint.build(msg);
 494         db.span_label(span, msg);
 495         if let Some((kind, id)) =
 496             is_enclosed(tcx, used_unsafe, id, unsafe_op_in_unsafe_fn_allowed(tcx, id))
 497         {
 498             db.span_label(
 499                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 500                 format!("because it's nested under this `unsafe` {}", kind),
 501             );
 502         }
 503         db.emit();
 504     });
 505 }
 506
 507 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 508     debug!("check_unsafety({:?})", def_id);
 509
 510     // closures are handled by their parent fn.
 511     if tcx.is_closure(def_id.to_def_id()) {
 512         return;
 513     }
 514
 515     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 516
 517     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 518         let (description, note) = details.description_and_note();
 519
 520         // Report an error.
 521         let unsafe_fn_msg =
 522             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 523
 524         match kind {
 525             UnsafetyViolationKind::General => {
 526                 // once
 527                 struct_span_err!(
 528                     tcx.sess,
 529                     source_info.span,
 530                     E0133,
 531                     "{} is unsafe and requires unsafe{} block",
 532                     description,
 533                     unsafe_fn_msg,
 534                 )
 535                 .span_label(source_info.span, description)
 536                 .note(note)
 537                 .emit();
 538             }
 539             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 540                 UNSAFE_OP_IN_UNSAFE_FN,
 541                 lint_root,
 542                 source_info.span,
 543                 |lint| {
 544                     lint.build(&format!(
 545                         "{} is unsafe and requires unsafe block (error E0133)",
 546                         description,
 547                     ))
 548                     .span_label(source_info.span, description)
 549                     .note(note)
 550                     .emit();
 551                 },
 552             ),
 553         }
 554     }
 555
 556     let (mut unsafe_used, mut unsafe_unused): (FxHashSet<_>, Vec<_>) = Default::default();
 557     for &(block_id, is_used) in unsafe_blocks.iter() {
 558         if is_used {
 559             unsafe_used.insert(block_id);
 560         } else {
 561             unsafe_unused.push(block_id);
 562         }
 563     }
 564     // The unused unsafe blocks might not be in source order; sort them so that the unused unsafe
 565     // error messages are properly aligned and the issue-45107 and lint-unused-unsafe tests pass.
 566     unsafe_unused.sort_by_cached_key(|hir_id| tcx.hir().span(*hir_id));
 567
 568     for &block_id in &unsafe_unused {
 569         report_unused_unsafe(tcx, &unsafe_used, block_id);
 570     }
 571 }
 572
 573 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 574     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 575 }