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     /// mark an `unsafe` block as used, so we don't lint it
  38     used_unsafe: FxHashSet<ast::NodeId>,
  39     inherited_blocks: Vec<(ast::NodeId, bool)>,
  40 }
  41
  42 impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
  43     fn new(
  44         min_const_fn: bool,
  45         mir: &'a Mir<'tcx>,
  46         source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  47         tcx: TyCtxt<'a, 'tcx, 'tcx>,
  48         param_env: ty::ParamEnv<'tcx>,
  49     ) -> Self {
  50         Self {
  51             mir,
  52             min_const_fn,
  53             source_scope_local_data,
  54             violations: vec![],
  55             source_info: SourceInfo {
  56                 span: mir.span,
  57                 scope: OUTERMOST_SOURCE_SCOPE
  58             },
  59             tcx,
  60             param_env,
  61             used_unsafe: Default::default(),
  62             inherited_blocks: vec![],
  63         }
  64     }
  65 }
  66
  67 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  68     fn visit_terminator(&mut self,
  69                         block: BasicBlock,
  70                         terminator: &Terminator<'tcx>,
  71                         location: Location)
  72     {
  73         self.source_info = terminator.source_info;
  74         match terminator.kind {
  75             TerminatorKind::Goto { .. } |
  76             TerminatorKind::SwitchInt { .. } |
  77             TerminatorKind::Drop { .. } |
  78             TerminatorKind::Yield { .. } |
  79             TerminatorKind::Assert { .. } |
  80             TerminatorKind::DropAndReplace { .. } |
  81             TerminatorKind::GeneratorDrop |
  82             TerminatorKind::Resume |
  83             TerminatorKind::Abort |
  84             TerminatorKind::Return |
  85             TerminatorKind::Unreachable |
  86             TerminatorKind::FalseEdges { .. } |
  87             TerminatorKind::FalseUnwind { .. } => {
  88                 // safe (at least as emitted during MIR construction)
  89             }
  90
  91             TerminatorKind::Call { ref func, .. } => {
  92                 let func_ty = func.ty(self.mir, self.tcx);
  93                 let sig = func_ty.fn_sig(self.tcx);
  94                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  95                     self.require_unsafe("call to unsafe function",
  96                         "consult the function's documentation for information on how to avoid \
  97                          undefined behavior", UnsafetyViolationKind::MinConstFn)
  98                 }
  99             }
 100         }
 101         self.super_terminator(block, terminator, location);
 102     }
 103
 104     fn visit_statement(&mut self,
 105                        block: BasicBlock,
 106                        statement: &Statement<'tcx>,
 107                        location: Location)
 108     {
 109         self.source_info = statement.source_info;
 110         match statement.kind {
 111             StatementKind::Assign(..) |
 112             StatementKind::FakeRead(..) |
 113             StatementKind::SetDiscriminant { .. } |
 114             StatementKind::StorageLive(..) |
 115             StatementKind::StorageDead(..) |
 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                     UnsafetyViolationKind::General)
 127             },
 128         }
 129         self.super_statement(block, statement, location);
 130     }
 131
 132     fn visit_rvalue(&mut self,
 133                     rvalue: &Rvalue<'tcx>,
 134                     location: Location)
 135     {
 136         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 137             match aggregate {
 138                 &AggregateKind::Array(..) |
 139                 &AggregateKind::Tuple |
 140                 &AggregateKind::Adt(..) => {}
 141                 &AggregateKind::Closure(def_id, _) |
 142                 &AggregateKind::Generator(def_id, _, _) => {
 143                     let UnsafetyCheckResult {
 144                         violations, unsafe_blocks
 145                     } = self.tcx.unsafety_check_result(def_id);
 146                     self.register_violations(&violations, &unsafe_blocks);
 147                 }
 148             }
 149         }
 150         self.super_rvalue(rvalue, location);
 151     }
 152
 153     fn visit_place(&mut self,
 154                     place: &Place<'tcx>,
 155                     context: PlaceContext<'tcx>,
 156                     location: Location) {
 157         if context.is_borrow() {
 158             if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 159                 let source_info = self.source_info;
 160                 let lint_root =
 161                     self.source_scope_local_data[source_info.scope].lint_root;
 162                 self.register_violations(&[UnsafetyViolation {
 163                     source_info,
 164                     description: Symbol::intern("borrow of packed field").as_interned_str(),
 165                     details:
 166                         Symbol::intern("fields of packed structs might be misaligned: \
 167                                         dereferencing a misaligned pointer or even just creating a \
 168                                         misaligned reference is undefined behavior")
 169                             .as_interned_str(),
 170                     kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 171                 }], &[]);
 172             }
 173         }
 174
 175         match place {
 176             &Place::Projection(box Projection {
 177                 ref base, ref elem
 178             }) => {
 179                 let old_source_info = self.source_info;
 180                 if let &Place::Local(local) = base {
 181                     if self.mir.local_decls[local].internal {
 182                         // Internal locals are used in the `move_val_init` desugaring.
 183                         // We want to check unsafety against the source info of the
 184                         // desugaring, rather than the source info of the RHS.
 185                         self.source_info = self.mir.local_decls[local].source_info;
 186                     }
 187                 }
 188                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 189                 match base_ty.sty {
 190                     ty::RawPtr(..) => {
 191                         self.require_unsafe("dereference of raw pointer",
 192                             "raw pointers may be NULL, dangling or unaligned; they can violate \
 193                              aliasing rules and cause data races: all of these are undefined \
 194                              behavior", UnsafetyViolationKind::General)
 195                     }
 196                     ty::Adt(adt, _) => {
 197                         if adt.is_union() {
 198                             if context == PlaceContext::MutatingUse(MutatingUseContext::Store) ||
 199                                 context == PlaceContext::MutatingUse(MutatingUseContext::Drop) ||
 200                                 context == PlaceContext::MutatingUse(
 201                                     MutatingUseContext::AsmOutput
 202                                 )
 203                             {
 204                                 let elem_ty = match elem {
 205                                     &ProjectionElem::Field(_, ty) => ty,
 206                                     _ => span_bug!(
 207                                         self.source_info.span,
 208                                         "non-field projection {:?} from union?",
 209                                         place)
 210                                 };
 211                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 212                                                             self.source_info.span) {
 213                                     self.require_unsafe(
 214                                         "assignment to non-`Copy` union field",
 215                                         "the previous content of the field will be dropped, which \
 216                                          causes undefined behavior if the field was not properly \
 217                                          initialized", UnsafetyViolationKind::General)
 218                                 } else {
 219                                     // write to non-move union, safe
 220                                 }
 221                             } else {
 222                                 self.require_unsafe("access to union field",
 223                                     "the field may not be properly initialized: using \
 224                                      uninitialized data will cause undefined behavior",
 225                                      UnsafetyViolationKind::General)
 226                             }
 227                         }
 228                     }
 229                     _ => {}
 230                 }
 231                 self.source_info = old_source_info;
 232             }
 233             &Place::Local(..) => {
 234                 // locals are safe
 235             }
 236             &Place::Promoted(_) => {
 237                 bug!("unsafety checking should happen before promotion")
 238             }
 239             &Place::Static(box Static { def_id, ty: _ }) => {
 240                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 241                     self.require_unsafe("use of mutable static",
 242                         "mutable statics can be mutated by multiple threads: aliasing violations \
 243                          or data races will cause undefined behavior",
 244                          UnsafetyViolationKind::General);
 245                 } else if self.tcx.is_foreign_item(def_id) {
 246                     let source_info = self.source_info;
 247                     let lint_root =
 248                         self.source_scope_local_data[source_info.scope].lint_root;
 249                     self.register_violations(&[UnsafetyViolation {
 250                         source_info,
 251                         description: Symbol::intern("use of extern static").as_interned_str(),
 252                         details:
 253                             Symbol::intern("extern statics are not controlled by the Rust type \
 254                                             system: invalid data, aliasing violations or data \
 255                                             races will cause undefined behavior")
 256                                 .as_interned_str(),
 257                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 258                     }], &[]);
 259                 }
 260             }
 261         };
 262         self.super_place(place, context, location);
 263     }
 264 }
 265
 266 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 267     fn require_unsafe(
 268         &mut self,
 269         description: &'static str,
 270         details: &'static str,
 271         kind: UnsafetyViolationKind,
 272     ) {
 273         let source_info = self.source_info;
 274         self.register_violations(&[UnsafetyViolation {
 275             source_info,
 276             description: Symbol::intern(description).as_interned_str(),
 277             details: Symbol::intern(details).as_interned_str(),
 278             kind,
 279         }], &[]);
 280     }
 281
 282     fn register_violations(&mut self,
 283                            violations: &[UnsafetyViolation],
 284                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 285         let safety = self.source_scope_local_data[self.source_info.scope].safety;
 286         let within_unsafe = match (safety, self.min_const_fn) {
 287             // FIXME: erring on the safe side here and disallowing builtin unsafety in const fn
 288             (Safety::BuiltinUnsafe, true) |
 289             // `unsafe` blocks are required even in `const unsafe fn`
 290             (Safety::FnUnsafe, true) |
 291             // `unsafe` blocks are required in safe code
 292             (Safety::Safe, _) => {
 293                 for violation in violations {
 294                     let mut violation = violation.clone();
 295                     if self.min_const_fn {
 296                         // overwrite unsafety violation in const fn with a single hard error kind
 297                         violation.kind = UnsafetyViolationKind::MinConstFn;
 298                     } else if let UnsafetyViolationKind::MinConstFn = violation.kind {
 299                         // outside of const fns we treat `MinConstFn` and `General` the same
 300                         violation.kind = UnsafetyViolationKind::General;
 301                     }
 302                     if !self.violations.contains(&violation) {
 303                         self.violations.push(violation)
 304                     }
 305                 }
 306                 false
 307             }
 308             (Safety::BuiltinUnsafe, false) | (Safety::FnUnsafe, false) => true,
 309             (Safety::ExplicitUnsafe(node_id), _) => {
 310                 if !violations.is_empty() {
 311                     self.used_unsafe.insert(node_id);
 312                 }
 313                 // only some unsafety is allowed in const fn
 314                 if self.min_const_fn {
 315                     for violation in violations {
 316                         match violation.kind {
 317                             // these are allowed
 318                             UnsafetyViolationKind::MinConstFn
 319                                 if self.tcx.sess.features_untracked().min_const_unsafe_fn => {},
 320                             _ => {
 321                                 let mut violation = violation.clone();
 322                                 // overwrite unsafety violation in const fn with a hard error
 323                                 violation.kind = UnsafetyViolationKind::MinConstFn;
 324                                 if !self.violations.contains(&violation) {
 325                                     self.violations.push(violation)
 326                                 }
 327                             },
 328                         }
 329                     }
 330                 }
 331                 true
 332             }
 333         };
 334         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 335             (node_id, is_used && !within_unsafe)
 336         }));
 337     }
 338 }
 339
 340 pub(crate) fn provide(providers: &mut Providers) {
 341     *providers = Providers {
 342         unsafety_check_result,
 343         unsafe_derive_on_repr_packed,
 344         ..*providers
 345     };
 346 }
 347
 348 struct UnusedUnsafeVisitor<'a> {
 349     used_unsafe: &'a FxHashSet<ast::NodeId>,
 350     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 351 }
 352
 353 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 354     fn nested_visit_map<'this>(&'this mut self) ->
 355         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 356     {
 357         hir::intravisit::NestedVisitorMap::None
 358     }
 359
 360     fn visit_block(&mut self, block: &'tcx hir::Block) {
 361         hir::intravisit::walk_block(self, block);
 362
 363         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 364             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 365         }
 366     }
 367 }
 368
 369 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 370                                  def_id: DefId,
 371                                  used_unsafe: &FxHashSet<ast::NodeId>,
 372                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 373 {
 374     let body_id =
 375         tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
 376             tcx.hir.maybe_body_owned_by(node_id)
 377         });
 378
 379     let body_id = match body_id {
 380         Some(body) => body,
 381         None => {
 382             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 383             return
 384         }
 385     };
 386     let body = tcx.hir.body(body_id);
 387     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 388            def_id, body, used_unsafe);
 389
 390     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 391     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 392 }
 393
 394 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 395                                    -> UnsafetyCheckResult
 396 {
 397     debug!("unsafety_violations({:?})", def_id);
 398
 399     // NB: this borrow is valid because all the consumers of
 400     // `mir_built` force this.
 401     let mir = &tcx.mir_built(def_id).borrow();
 402
 403     let source_scope_local_data = match mir.source_scope_local_data {
 404         ClearCrossCrate::Set(ref data) => data,
 405         ClearCrossCrate::Clear => {
 406             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 407             return UnsafetyCheckResult {
 408                 violations: Lrc::new([]),
 409                 unsafe_blocks: Lrc::new([])
 410             }
 411         }
 412     };
 413
 414     let param_env = tcx.param_env(def_id);
 415     let mut checker = UnsafetyChecker::new(
 416         tcx.is_const_fn(def_id) && tcx.is_min_const_fn(def_id),
 417         mir, source_scope_local_data, tcx, param_env);
 418     checker.visit_mir(mir);
 419
 420     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 421     UnsafetyCheckResult {
 422         violations: checker.violations.into(),
 423         unsafe_blocks: checker.inherited_blocks.into()
 424     }
 425 }
 426
 427 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 428     let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
 429         Some(node_id) => node_id,
 430         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 431     };
 432
 433     // FIXME: when we make this a hard error, this should have its
 434     // own error code.
 435     let message = if tcx.generics_of(def_id).own_counts().types != 0 {
 436         "#[derive] can't be used on a #[repr(packed)] struct with \
 437          type parameters (error E0133)".to_string()
 438     } else {
 439         "#[derive] can't be used on a #[repr(packed)] struct that \
 440          does not derive Copy (error E0133)".to_string()
 441     };
 442     tcx.lint_node(SAFE_PACKED_BORROWS,
 443                   lint_node_id,
 444                   tcx.def_span(def_id),
 445                   &message);
 446 }
 447
 448 /// Return the NodeId for an enclosing scope that is also `unsafe`
 449 fn is_enclosed(tcx: TyCtxt,
 450                used_unsafe: &FxHashSet<ast::NodeId>,
 451                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 452     let parent_id = tcx.hir.get_parent_node(id);
 453     if parent_id != id {
 454         if used_unsafe.contains(&parent_id) {
 455             Some(("block".to_string(), parent_id))
 456         } else if let Some(Node::Item(&hir::Item {
 457             node: hir::ItemKind::Fn(_, header, _, _),
 458             ..
 459         })) = tcx.hir.find(parent_id) {
 460             match header.unsafety {
 461                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 462                 hir::Unsafety::Normal => None,
 463             }
 464         } else {
 465             is_enclosed(tcx, used_unsafe, parent_id)
 466         }
 467     } else {
 468         None
 469     }
 470 }
 471
 472 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 473     let span = tcx.sess.source_map().def_span(tcx.hir.span(id));
 474     let msg = "unnecessary `unsafe` block";
 475     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 476     db.span_label(span, msg);
 477     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 478         db.span_label(tcx.sess.source_map().def_span(tcx.hir.span(id)),
 479                       format!("because it's nested under this `unsafe` {}", kind));
 480     }
 481     db.emit();
 482 }
 483
 484 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 485     debug!("builtin_derive_def_id({:?})", def_id);
 486     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 487         if tcx.has_attr(impl_def_id, "automatically_derived") {
 488             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 489             Some(impl_def_id)
 490         } else {
 491             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 492             None
 493         }
 494     } else {
 495         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 496         None
 497     }
 498 }
 499
 500 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 501     debug!("check_unsafety({:?})", def_id);
 502
 503     // closures are handled by their parent fn.
 504     if tcx.is_closure(def_id) {
 505         return;
 506     }
 507
 508     let UnsafetyCheckResult {
 509         violations,
 510         unsafe_blocks
 511     } = tcx.unsafety_check_result(def_id);
 512
 513     for &UnsafetyViolation {
 514         source_info, description, details, kind
 515     } in violations.iter() {
 516         // Report an error.
 517         match kind {
 518             UnsafetyViolationKind::General => {
 519                 struct_span_err!(
 520                     tcx.sess, source_info.span, E0133,
 521                     "{} is unsafe and requires unsafe function or block", description)
 522                     .span_label(source_info.span, &description.as_str()[..])
 523                     .note(&details.as_str()[..])
 524                     .emit();
 525             }
 526             UnsafetyViolationKind::MinConstFn => {
 527                 tcx.sess.struct_span_err(
 528                     source_info.span,
 529                     &format!("{} is unsafe and unsafe operations \
 530                             are not allowed in const fn", description))
 531                     .span_label(source_info.span, &description.as_str()[..])
 532                     .note(&details.as_str()[..])
 533                     .emit();
 534             }
 535             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 536                 tcx.lint_node_note(SAFE_EXTERN_STATICS,
 537                               lint_node_id,
 538                               source_info.span,
 539                               &format!("{} is unsafe and requires unsafe function or block \
 540                                         (error E0133)", &description.as_str()[..]),
 541                               &details.as_str()[..]);
 542             }
 543             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 544                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 545                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 546                 } else {
 547                     tcx.lint_node_note(SAFE_PACKED_BORROWS,
 548                                   lint_node_id,
 549                                   source_info.span,
 550                                   &format!("{} is unsafe and requires unsafe function or block \
 551                                             (error E0133)", &description.as_str()[..]),
 552                                   &details.as_str()[..]);
 553                 }
 554             }
 555         }
 556     }
 557
 558     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 559     unsafe_blocks.sort();
 560     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 561         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 562         .collect();
 563     for &(block_id, is_used) in unsafe_blocks {
 564         if !is_used {
 565             report_unused_unsafe(tcx, &used_unsafe, block_id);
 566         }
 567     }
 568 }