src/librustc_mir/transform/check_unsafety.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc_data_structures::fx::FxHashSet;
  12 use rustc_data_structures::indexed_vec::IndexVec;
  13 use rustc_data_structures::sync::Lrc;
  14
  15 use rustc::ty::query::Providers;
  16 use rustc::ty::{self, TyCtxt};
  17 use rustc::hir;
  18 use rustc::hir::Node;
  19 use rustc::hir::def_id::DefId;
  20 use rustc::lint::builtin::{SAFE_EXTERN_STATICS, SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
  21 use rustc::mir::*;
  22 use rustc::mir::visit::{PlaceContext, Visitor, MutatingUseContext};
  23
  24 use syntax::ast;
  25 use syntax::symbol::Symbol;
  26
  27 use util;
  28
  29 pub struct UnsafetyChecker<'a, 'tcx: 'a> {
  30     mir: &'a Mir<'tcx>,
  31     min_const_fn: bool,
  32     source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  33     violations: Vec<UnsafetyViolation>,
  34     source_info: SourceInfo,
  35     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  36     param_env: ty::ParamEnv<'tcx>,
  37     used_unsafe: FxHashSet<ast::NodeId>,
  38     inherited_blocks: Vec<(ast::NodeId, bool)>,
  39 }
  40
  41 impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
  42     fn new(
  43         min_const_fn: bool,
  44         mir: &'a Mir<'tcx>,
  45         source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  46         tcx: TyCtxt<'a, 'tcx, 'tcx>,
  47         param_env: ty::ParamEnv<'tcx>,
  48     ) -> Self {
  49         Self {
  50             mir,
  51             min_const_fn,
  52             source_scope_local_data,
  53             violations: vec![],
  54             source_info: SourceInfo {
  55                 span: mir.span,
  56                 scope: OUTERMOST_SOURCE_SCOPE
  57             },
  58             tcx,
  59             param_env,
  60             used_unsafe: Default::default(),
  61             inherited_blocks: vec![],
  62         }
  63     }
  64 }
  65
  66 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  67     fn visit_terminator(&mut self,
  68                         block: BasicBlock,
  69                         terminator: &Terminator<'tcx>,
  70                         location: Location)
  71     {
  72         self.source_info = terminator.source_info;
  73         match terminator.kind {
  74             TerminatorKind::Goto { .. } |
  75             TerminatorKind::SwitchInt { .. } |
  76             TerminatorKind::Drop { .. } |
  77             TerminatorKind::Yield { .. } |
  78             TerminatorKind::Assert { .. } |
  79             TerminatorKind::DropAndReplace { .. } |
  80             TerminatorKind::GeneratorDrop |
  81             TerminatorKind::Resume |
  82             TerminatorKind::Abort |
  83             TerminatorKind::Return |
  84             TerminatorKind::Unreachable |
  85             TerminatorKind::FalseEdges { .. } |
  86             TerminatorKind::FalseUnwind { .. } => {
  87                 // safe (at least as emitted during MIR construction)
  88             }
  89
  90             TerminatorKind::Call { ref func, .. } => {
  91                 let func_ty = func.ty(self.mir, self.tcx);
  92                 let sig = func_ty.fn_sig(self.tcx);
  93                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  94                     self.require_unsafe("call to unsafe function",
  95                         "consult the function's documentation for information on how to avoid \
  96                          undefined behavior")
  97                 }
  98             }
  99         }
 100         self.super_terminator(block, terminator, location);
 101     }
 102
 103     fn visit_statement(&mut self,
 104                        block: BasicBlock,
 105                        statement: &Statement<'tcx>,
 106                        location: Location)
 107     {
 108         self.source_info = statement.source_info;
 109         match statement.kind {
 110             StatementKind::Assign(..) |
 111             StatementKind::FakeRead(..) |
 112             StatementKind::SetDiscriminant { .. } |
 113             StatementKind::StorageLive(..) |
 114             StatementKind::StorageDead(..) |
 115             StatementKind::EndRegion(..) |
 116             StatementKind::Retag { .. } |
 117             StatementKind::EscapeToRaw { .. } |
 118             StatementKind::AscribeUserType(..) |
 119             StatementKind::Nop => {
 120                 // safe (at least as emitted during MIR construction)
 121             }
 122
 123             StatementKind::InlineAsm { .. } => {
 124                 self.require_unsafe("use of inline assembly",
 125                     "inline assembly is entirely unchecked and can cause undefined behavior")
 126             },
 127         }
 128         self.super_statement(block, statement, location);
 129     }
 130
 131     fn visit_rvalue(&mut self,
 132                     rvalue: &Rvalue<'tcx>,
 133                     location: Location)
 134     {
 135         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 136             match aggregate {
 137                 &AggregateKind::Array(..) |
 138                 &AggregateKind::Tuple |
 139                 &AggregateKind::Adt(..) => {}
 140                 &AggregateKind::Closure(def_id, _) |
 141                 &AggregateKind::Generator(def_id, _, _) => {
 142                     let UnsafetyCheckResult {
 143                         violations, unsafe_blocks
 144                     } = self.tcx.unsafety_check_result(def_id);
 145                     self.register_violations(&violations, &unsafe_blocks);
 146                 }
 147             }
 148         }
 149         self.super_rvalue(rvalue, location);
 150     }
 151
 152     fn visit_place(&mut self,
 153                     place: &Place<'tcx>,
 154                     context: PlaceContext<'tcx>,
 155                     location: Location) {
 156         if context.is_borrow() {
 157             if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 158                 let source_info = self.source_info;
 159                 let lint_root =
 160                     self.source_scope_local_data[source_info.scope].lint_root;
 161                 self.register_violations(&[UnsafetyViolation {
 162                     source_info,
 163                     description: Symbol::intern("borrow of packed field").as_interned_str(),
 164                     details:
 165                         Symbol::intern("fields of packed structs might be misaligned: \
 166                                         dereferencing a misaligned pointer or even just creating a \
 167                                         misaligned reference is undefined behavior")
 168                             .as_interned_str(),
 169                     kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 170                 }], &[]);
 171             }
 172         }
 173
 174         match place {
 175             &Place::Projection(box Projection {
 176                 ref base, ref elem
 177             }) => {
 178                 let old_source_info = self.source_info;
 179                 if let &Place::Local(local) = base {
 180                     if self.mir.local_decls[local].internal {
 181                         // Internal locals are used in the `move_val_init` desugaring.
 182                         // We want to check unsafety against the source info of the
 183                         // desugaring, rather than the source info of the RHS.
 184                         self.source_info = self.mir.local_decls[local].source_info;
 185                     }
 186                 }
 187                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 188                 match base_ty.sty {
 189                     ty::RawPtr(..) => {
 190                         self.require_unsafe("dereference of raw pointer",
 191                             "raw pointers may be NULL, dangling or unaligned; they can violate \
 192                              aliasing rules and cause data races: all of these are undefined \
 193                              behavior")
 194                     }
 195                     ty::Adt(adt, _) => {
 196                         if adt.is_union() {
 197                             if context == PlaceContext::MutatingUse(MutatingUseContext::Store) ||
 198                                 context == PlaceContext::MutatingUse(MutatingUseContext::Drop) ||
 199                                 context == PlaceContext::MutatingUse(
 200                                     MutatingUseContext::AsmOutput
 201                                 )
 202                             {
 203                                 let elem_ty = match elem {
 204                                     &ProjectionElem::Field(_, ty) => ty,
 205                                     _ => span_bug!(
 206                                         self.source_info.span,
 207                                         "non-field projection {:?} from union?",
 208                                         place)
 209                                 };
 210                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 211                                                             self.source_info.span) {
 212                                     self.require_unsafe(
 213                                         "assignment to non-`Copy` union field",
 214                                         "the previous content of the field will be dropped, which \
 215                                          causes undefined behavior if the field was not properly \
 216                                          initialized")
 217                                 } else {
 218                                     // write to non-move union, safe
 219                                 }
 220                             } else {
 221                                 self.require_unsafe("access to union field",
 222                                     "the field may not be properly initialized: using \
 223                                      uninitialized data will cause undefined behavior")
 224                             }
 225                         }
 226                     }
 227                     _ => {}
 228                 }
 229                 self.source_info = old_source_info;
 230             }
 231             &Place::Local(..) => {
 232                 // locals are safe
 233             }
 234             &Place::Promoted(_) => {
 235                 bug!("unsafety checking should happen before promotion")
 236             }
 237             &Place::Static(box Static { def_id, ty: _ }) => {
 238                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 239                     self.require_unsafe("use of mutable static",
 240                         "mutable statics can be mutated by multiple threads: aliasing violations \
 241                          or data races will cause undefined behavior");
 242                 } else if self.tcx.is_foreign_item(def_id) {
 243                     let source_info = self.source_info;
 244                     let lint_root =
 245                         self.source_scope_local_data[source_info.scope].lint_root;
 246                     self.register_violations(&[UnsafetyViolation {
 247                         source_info,
 248                         description: Symbol::intern("use of extern static").as_interned_str(),
 249                         details:
 250                             Symbol::intern("extern statics are not controlled by the Rust type \
 251                                             system: invalid data, aliasing violations or data \
 252                                             races will cause undefined behavior")
 253                                 .as_interned_str(),
 254                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 255                     }], &[]);
 256                 }
 257             }
 258         };
 259         self.super_place(place, context, location);
 260     }
 261 }
 262
 263 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 264     fn require_unsafe(&mut self,
 265                       description: &'static str,
 266                       details: &'static str)
 267     {
 268         let source_info = self.source_info;
 269         self.register_violations(&[UnsafetyViolation {
 270             source_info,
 271             description: Symbol::intern(description).as_interned_str(),
 272             details: Symbol::intern(details).as_interned_str(),
 273             kind: UnsafetyViolationKind::General,
 274         }], &[]);
 275     }
 276
 277     fn register_violations(&mut self,
 278                            violations: &[UnsafetyViolation],
 279                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 280         if self.min_const_fn {
 281             for violation in violations {
 282                 let mut violation = violation.clone();
 283                 violation.kind = UnsafetyViolationKind::MinConstFn;
 284                 if !self.violations.contains(&violation) {
 285                     self.violations.push(violation)
 286                 }
 287             }
 288         }
 289         let within_unsafe = match self.source_scope_local_data[self.source_info.scope].safety {
 290             Safety::Safe => {
 291                 for violation in violations {
 292                     if !self.violations.contains(violation) {
 293                         self.violations.push(violation.clone())
 294                     }
 295                 }
 296                 false
 297             }
 298             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 299             Safety::ExplicitUnsafe(node_id) => {
 300                 if !violations.is_empty() {
 301                     self.used_unsafe.insert(node_id);
 302                 }
 303                 true
 304             }
 305         };
 306         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 307             (node_id, is_used && !within_unsafe)
 308         }));
 309     }
 310 }
 311
 312 pub(crate) fn provide(providers: &mut Providers) {
 313     *providers = Providers {
 314         unsafety_check_result,
 315         unsafe_derive_on_repr_packed,
 316         ..*providers
 317     };
 318 }
 319
 320 struct UnusedUnsafeVisitor<'a> {
 321     used_unsafe: &'a FxHashSet<ast::NodeId>,
 322     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 323 }
 324
 325 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 326     fn nested_visit_map<'this>(&'this mut self) ->
 327         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 328     {
 329         hir::intravisit::NestedVisitorMap::None
 330     }
 331
 332     fn visit_block(&mut self, block: &'tcx hir::Block) {
 333         hir::intravisit::walk_block(self, block);
 334
 335         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 336             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 337         }
 338     }
 339 }
 340
 341 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 342                                  def_id: DefId,
 343                                  used_unsafe: &FxHashSet<ast::NodeId>,
 344                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 345 {
 346     let body_id =
 347         tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
 348             tcx.hir.maybe_body_owned_by(node_id)
 349         });
 350
 351     let body_id = match body_id {
 352         Some(body) => body,
 353         None => {
 354             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 355             return
 356         }
 357     };
 358     let body = tcx.hir.body(body_id);
 359     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 360            def_id, body, used_unsafe);
 361
 362     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 363     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 364 }
 365
 366 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 367                                    -> UnsafetyCheckResult
 368 {
 369     debug!("unsafety_violations({:?})", def_id);
 370
 371     // NB: this borrow is valid because all the consumers of
 372     // `mir_built` force this.
 373     let mir = &tcx.mir_built(def_id).borrow();
 374
 375     let source_scope_local_data = match mir.source_scope_local_data {
 376         ClearCrossCrate::Set(ref data) => data,
 377         ClearCrossCrate::Clear => {
 378             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 379             return UnsafetyCheckResult {
 380                 violations: Lrc::new([]),
 381                 unsafe_blocks: Lrc::new([])
 382             }
 383         }
 384     };
 385
 386     let param_env = tcx.param_env(def_id);
 387     let mut checker = UnsafetyChecker::new(
 388         tcx.is_const_fn(def_id) && tcx.is_min_const_fn(def_id),
 389         mir, source_scope_local_data, tcx, param_env);
 390     checker.visit_mir(mir);
 391
 392     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 393     UnsafetyCheckResult {
 394         violations: checker.violations.into(),
 395         unsafe_blocks: checker.inherited_blocks.into()
 396     }
 397 }
 398
 399 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 400     let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
 401         Some(node_id) => node_id,
 402         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 403     };
 404
 405     // FIXME: when we make this a hard error, this should have its
 406     // own error code.
 407     let message = if tcx.generics_of(def_id).own_counts().types != 0 {
 408         "#[derive] can't be used on a #[repr(packed)] struct with \
 409          type parameters (error E0133)".to_string()
 410     } else {
 411         "#[derive] can't be used on a #[repr(packed)] struct that \
 412          does not derive Copy (error E0133)".to_string()
 413     };
 414     tcx.lint_node(SAFE_PACKED_BORROWS,
 415                   lint_node_id,
 416                   tcx.def_span(def_id),
 417                   &message);
 418 }
 419
 420 /// Return the NodeId for an enclosing scope that is also `unsafe`
 421 fn is_enclosed(tcx: TyCtxt,
 422                used_unsafe: &FxHashSet<ast::NodeId>,
 423                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 424     let parent_id = tcx.hir.get_parent_node(id);
 425     if parent_id != id {
 426         if used_unsafe.contains(&parent_id) {
 427             Some(("block".to_string(), parent_id))
 428         } else if let Some(Node::Item(&hir::Item {
 429             node: hir::ItemKind::Fn(_, header, _, _),
 430             ..
 431         })) = tcx.hir.find(parent_id) {
 432             match header.unsafety {
 433                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 434                 hir::Unsafety::Normal => None,
 435             }
 436         } else {
 437             is_enclosed(tcx, used_unsafe, parent_id)
 438         }
 439     } else {
 440         None
 441     }
 442 }
 443
 444 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 445     let span = tcx.sess.source_map().def_span(tcx.hir.span(id));
 446     let msg = "unnecessary `unsafe` block";
 447     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 448     db.span_label(span, msg);
 449     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 450         db.span_label(tcx.sess.source_map().def_span(tcx.hir.span(id)),
 451                       format!("because it's nested under this `unsafe` {}", kind));
 452     }
 453     db.emit();
 454 }
 455
 456 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 457     debug!("builtin_derive_def_id({:?})", def_id);
 458     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 459         if tcx.has_attr(impl_def_id, "automatically_derived") {
 460             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 461             Some(impl_def_id)
 462         } else {
 463             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 464             None
 465         }
 466     } else {
 467         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 468         None
 469     }
 470 }
 471
 472 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 473     debug!("check_unsafety({:?})", def_id);
 474
 475     // closures are handled by their parent fn.
 476     if tcx.is_closure(def_id) {
 477         return;
 478     }
 479
 480     let UnsafetyCheckResult {
 481         violations,
 482         unsafe_blocks
 483     } = tcx.unsafety_check_result(def_id);
 484
 485     for &UnsafetyViolation {
 486         source_info, description, details, kind
 487     } in violations.iter() {
 488         // Report an error.
 489         match kind {
 490             UnsafetyViolationKind::General => {
 491                 struct_span_err!(
 492                     tcx.sess, source_info.span, E0133,
 493                     "{} is unsafe and requires unsafe function or block", description)
 494                     .span_label(source_info.span, &description.as_str()[..])
 495                     .note(&details.as_str()[..])
 496                     .emit();
 497             }
 498             UnsafetyViolationKind::MinConstFn => {
 499                 tcx.sess.struct_span_err(
 500                     source_info.span,
 501                     &format!("{} is unsafe and unsafe operations \
 502                             are not allowed in const fn", description))
 503                     .span_label(source_info.span, &description.as_str()[..])
 504                     .note(&details.as_str()[..])
 505                     .emit();
 506             }
 507             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 508                 tcx.lint_node_note(SAFE_EXTERN_STATICS,
 509                               lint_node_id,
 510                               source_info.span,
 511                               &format!("{} is unsafe and requires unsafe function or block \
 512                                         (error E0133)", &description.as_str()[..]),
 513                               &details.as_str()[..]);
 514             }
 515             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 516                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 517                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 518                 } else {
 519                     tcx.lint_node_note(SAFE_PACKED_BORROWS,
 520                                   lint_node_id,
 521                                   source_info.span,
 522                                   &format!("{} is unsafe and requires unsafe function or block \
 523                                             (error E0133)", &description.as_str()[..]),
 524                                   &details.as_str()[..]);
 525                 }
 526             }
 527         }
 528     }
 529
 530     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 531     unsafe_blocks.sort();
 532     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 533         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 534         .collect();
 535     for &(block_id, is_used) in unsafe_blocks {
 536         if !is_used {
 537             report_unused_unsafe(tcx, &used_unsafe, block_id);
 538         }
 539     }
 540 }