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