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::Retag { .. } |
 116             StatementKind::EscapeToRaw { .. } |
 117             StatementKind::AscribeUserType(..) |
 118             StatementKind::Nop => {
 119                 // safe (at least as emitted during MIR construction)
 120             }
 121
 122             StatementKind::InlineAsm { .. } => {
 123                 self.require_unsafe("use of inline assembly",
 124                     "inline assembly is entirely unchecked and can cause undefined behavior")
 125             },
 126         }
 127         self.super_statement(block, statement, location);
 128     }
 129
 130     fn visit_rvalue(&mut self,
 131                     rvalue: &Rvalue<'tcx>,
 132                     location: Location)
 133     {
 134         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 135             match aggregate {
 136                 &AggregateKind::Array(..) |
 137                 &AggregateKind::Tuple |
 138                 &AggregateKind::Adt(..) => {}
 139                 &AggregateKind::Closure(def_id, _) |
 140                 &AggregateKind::Generator(def_id, _, _) => {
 141                     let UnsafetyCheckResult {
 142                         violations, unsafe_blocks
 143                     } = self.tcx.unsafety_check_result(def_id);
 144                     self.register_violations(&violations, &unsafe_blocks);
 145                 }
 146             }
 147         }
 148         self.super_rvalue(rvalue, location);
 149     }
 150
 151     fn visit_place(&mut self,
 152                     place: &Place<'tcx>,
 153                     context: PlaceContext<'tcx>,
 154                     location: Location) {
 155         if context.is_borrow() {
 156             if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 157                 let source_info = self.source_info;
 158                 let lint_root =
 159                     self.source_scope_local_data[source_info.scope].lint_root;
 160                 self.register_violations(&[UnsafetyViolation {
 161                     source_info,
 162                     description: Symbol::intern("borrow of packed field").as_interned_str(),
 163                     details:
 164                         Symbol::intern("fields of packed structs might be misaligned: \
 165                                         dereferencing a misaligned pointer or even just creating a \
 166                                         misaligned reference is undefined behavior")
 167                             .as_interned_str(),
 168                     kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 169                 }], &[]);
 170             }
 171         }
 172
 173         match place {
 174             &Place::Projection(box Projection {
 175                 ref base, ref elem
 176             }) => {
 177                 let old_source_info = self.source_info;
 178                 if let &Place::Local(local) = base {
 179                     if self.mir.local_decls[local].internal {
 180                         // Internal locals are used in the `move_val_init` desugaring.
 181                         // We want to check unsafety against the source info of the
 182                         // desugaring, rather than the source info of the RHS.
 183                         self.source_info = self.mir.local_decls[local].source_info;
 184                     }
 185                 }
 186                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 187                 match base_ty.sty {
 188                     ty::RawPtr(..) => {
 189                         self.require_unsafe("dereference of raw pointer",
 190                             "raw pointers may be NULL, dangling or unaligned; they can violate \
 191                              aliasing rules and cause data races: all of these are undefined \
 192                              behavior")
 193                     }
 194                     ty::Adt(adt, _) => {
 195                         if adt.is_union() {
 196                             if context == PlaceContext::MutatingUse(MutatingUseContext::Store) ||
 197                                 context == PlaceContext::MutatingUse(MutatingUseContext::Drop) ||
 198                                 context == PlaceContext::MutatingUse(
 199                                     MutatingUseContext::AsmOutput
 200                                 )
 201                             {
 202                                 let elem_ty = match elem {
 203                                     &ProjectionElem::Field(_, ty) => ty,
 204                                     _ => span_bug!(
 205                                         self.source_info.span,
 206                                         "non-field projection {:?} from union?",
 207                                         place)
 208                                 };
 209                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 210                                                             self.source_info.span) {
 211                                     self.require_unsafe(
 212                                         "assignment to non-`Copy` union field",
 213                                         "the previous content of the field will be dropped, which \
 214                                          causes undefined behavior if the field was not properly \
 215                                          initialized")
 216                                 } else {
 217                                     // write to non-move union, safe
 218                                 }
 219                             } else {
 220                                 self.require_unsafe("access to union field",
 221                                     "the field may not be properly initialized: using \
 222                                      uninitialized data will cause undefined behavior")
 223                             }
 224                         }
 225                     }
 226                     _ => {}
 227                 }
 228                 self.source_info = old_source_info;
 229             }
 230             &Place::Local(..) => {
 231                 // locals are safe
 232             }
 233             &Place::Promoted(_) => {
 234                 bug!("unsafety checking should happen before promotion")
 235             }
 236             &Place::Static(box Static { def_id, ty: _ }) => {
 237                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 238                     self.require_unsafe("use of mutable static",
 239                         "mutable statics can be mutated by multiple threads: aliasing violations \
 240                          or data races will cause undefined behavior");
 241                 } else if self.tcx.is_foreign_item(def_id) {
 242                     let source_info = self.source_info;
 243                     let lint_root =
 244                         self.source_scope_local_data[source_info.scope].lint_root;
 245                     self.register_violations(&[UnsafetyViolation {
 246                         source_info,
 247                         description: Symbol::intern("use of extern static").as_interned_str(),
 248                         details:
 249                             Symbol::intern("extern statics are not controlled by the Rust type \
 250                                             system: invalid data, aliasing violations or data \
 251                                             races will cause undefined behavior")
 252                                 .as_interned_str(),
 253                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 254                     }], &[]);
 255                 }
 256             }
 257         };
 258         self.super_place(place, context, location);
 259     }
 260 }
 261
 262 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 263     fn require_unsafe(&mut self,
 264                       description: &'static str,
 265                       details: &'static str)
 266     {
 267         let source_info = self.source_info;
 268         self.register_violations(&[UnsafetyViolation {
 269             source_info,
 270             description: Symbol::intern(description).as_interned_str(),
 271             details: Symbol::intern(details).as_interned_str(),
 272             kind: UnsafetyViolationKind::General,
 273         }], &[]);
 274     }
 275
 276     fn register_violations(&mut self,
 277                            violations: &[UnsafetyViolation],
 278                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 279         if self.min_const_fn {
 280             for violation in violations {
 281                 let mut violation = violation.clone();
 282                 violation.kind = UnsafetyViolationKind::MinConstFn;
 283                 if !self.violations.contains(&violation) {
 284                     self.violations.push(violation)
 285                 }
 286             }
 287         }
 288         let within_unsafe = match self.source_scope_local_data[self.source_info.scope].safety {
 289             Safety::Safe => {
 290                 for violation in violations {
 291                     if !self.violations.contains(violation) {
 292                         self.violations.push(violation.clone())
 293                     }
 294                 }
 295                 false
 296             }
 297             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 298             Safety::ExplicitUnsafe(node_id) => {
 299                 if !violations.is_empty() {
 300                     self.used_unsafe.insert(node_id);
 301                 }
 302                 true
 303             }
 304         };
 305         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 306             (node_id, is_used && !within_unsafe)
 307         }));
 308     }
 309 }
 310
 311 pub(crate) fn provide(providers: &mut Providers) {
 312     *providers = Providers {
 313         unsafety_check_result,
 314         unsafe_derive_on_repr_packed,
 315         ..*providers
 316     };
 317 }
 318
 319 struct UnusedUnsafeVisitor<'a> {
 320     used_unsafe: &'a FxHashSet<ast::NodeId>,
 321     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 322 }
 323
 324 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 325     fn nested_visit_map<'this>(&'this mut self) ->
 326         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 327     {
 328         hir::intravisit::NestedVisitorMap::None
 329     }
 330
 331     fn visit_block(&mut self, block: &'tcx hir::Block) {
 332         hir::intravisit::walk_block(self, block);
 333
 334         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 335             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 336         }
 337     }
 338 }
 339
 340 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 341                                  def_id: DefId,
 342                                  used_unsafe: &FxHashSet<ast::NodeId>,
 343                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 344 {
 345     let body_id =
 346         tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
 347             tcx.hir.maybe_body_owned_by(node_id)
 348         });
 349
 350     let body_id = match body_id {
 351         Some(body) => body,
 352         None => {
 353             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 354             return
 355         }
 356     };
 357     let body = tcx.hir.body(body_id);
 358     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 359            def_id, body, used_unsafe);
 360
 361     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 362     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 363 }
 364
 365 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 366                                    -> UnsafetyCheckResult
 367 {
 368     debug!("unsafety_violations({:?})", def_id);
 369
 370     // NB: this borrow is valid because all the consumers of
 371     // `mir_built` force this.
 372     let mir = &tcx.mir_built(def_id).borrow();
 373
 374     let source_scope_local_data = match mir.source_scope_local_data {
 375         ClearCrossCrate::Set(ref data) => data,
 376         ClearCrossCrate::Clear => {
 377             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 378             return UnsafetyCheckResult {
 379                 violations: Lrc::new([]),
 380                 unsafe_blocks: Lrc::new([])
 381             }
 382         }
 383     };
 384
 385     let param_env = tcx.param_env(def_id);
 386     let mut checker = UnsafetyChecker::new(
 387         tcx.is_const_fn(def_id) && tcx.is_min_const_fn(def_id),
 388         mir, source_scope_local_data, tcx, param_env);
 389     checker.visit_mir(mir);
 390
 391     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 392     UnsafetyCheckResult {
 393         violations: checker.violations.into(),
 394         unsafe_blocks: checker.inherited_blocks.into()
 395     }
 396 }
 397
 398 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 399     let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
 400         Some(node_id) => node_id,
 401         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 402     };
 403
 404     // FIXME: when we make this a hard error, this should have its
 405     // own error code.
 406     let message = if tcx.generics_of(def_id).own_counts().types != 0 {
 407         "#[derive] can't be used on a #[repr(packed)] struct with \
 408          type parameters (error E0133)".to_string()
 409     } else {
 410         "#[derive] can't be used on a #[repr(packed)] struct that \
 411          does not derive Copy (error E0133)".to_string()
 412     };
 413     tcx.lint_node(SAFE_PACKED_BORROWS,
 414                   lint_node_id,
 415                   tcx.def_span(def_id),
 416                   &message);
 417 }
 418
 419 /// Return the NodeId for an enclosing scope that is also `unsafe`
 420 fn is_enclosed(tcx: TyCtxt,
 421                used_unsafe: &FxHashSet<ast::NodeId>,
 422                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 423     let parent_id = tcx.hir.get_parent_node(id);
 424     if parent_id != id {
 425         if used_unsafe.contains(&parent_id) {
 426             Some(("block".to_string(), parent_id))
 427         } else if let Some(Node::Item(&hir::Item {
 428             node: hir::ItemKind::Fn(_, header, _, _),
 429             ..
 430         })) = tcx.hir.find(parent_id) {
 431             match header.unsafety {
 432                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 433                 hir::Unsafety::Normal => None,
 434             }
 435         } else {
 436             is_enclosed(tcx, used_unsafe, parent_id)
 437         }
 438     } else {
 439         None
 440     }
 441 }
 442
 443 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 444     let span = tcx.sess.source_map().def_span(tcx.hir.span(id));
 445     let msg = "unnecessary `unsafe` block";
 446     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 447     db.span_label(span, msg);
 448     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 449         db.span_label(tcx.sess.source_map().def_span(tcx.hir.span(id)),
 450                       format!("because it's nested under this `unsafe` {}", kind));
 451     }
 452     db.emit();
 453 }
 454
 455 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 456     debug!("builtin_derive_def_id({:?})", def_id);
 457     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 458         if tcx.has_attr(impl_def_id, "automatically_derived") {
 459             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 460             Some(impl_def_id)
 461         } else {
 462             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 463             None
 464         }
 465     } else {
 466         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 467         None
 468     }
 469 }
 470
 471 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 472     debug!("check_unsafety({:?})", def_id);
 473
 474     // closures are handled by their parent fn.
 475     if tcx.is_closure(def_id) {
 476         return;
 477     }
 478
 479     let UnsafetyCheckResult {
 480         violations,
 481         unsafe_blocks
 482     } = tcx.unsafety_check_result(def_id);
 483
 484     for &UnsafetyViolation {
 485         source_info, description, details, kind
 486     } in violations.iter() {
 487         // Report an error.
 488         match kind {
 489             UnsafetyViolationKind::General => {
 490                 struct_span_err!(
 491                     tcx.sess, source_info.span, E0133,
 492                     "{} is unsafe and requires unsafe function or block", description)
 493                     .span_label(source_info.span, &description.as_str()[..])
 494                     .note(&details.as_str()[..])
 495                     .emit();
 496             }
 497             UnsafetyViolationKind::MinConstFn => {
 498                 tcx.sess.struct_span_err(
 499                     source_info.span,
 500                     &format!("{} is unsafe and unsafe operations \
 501                             are not allowed in const fn", description))
 502                     .span_label(source_info.span, &description.as_str()[..])
 503                     .note(&details.as_str()[..])
 504                     .emit();
 505             }
 506             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 507                 tcx.lint_node_note(SAFE_EXTERN_STATICS,
 508                               lint_node_id,
 509                               source_info.span,
 510                               &format!("{} is unsafe and requires unsafe function or block \
 511                                         (error E0133)", &description.as_str()[..]),
 512                               &details.as_str()[..]);
 513             }
 514             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 515                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 516                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 517                 } else {
 518                     tcx.lint_node_note(SAFE_PACKED_BORROWS,
 519                                   lint_node_id,
 520                                   source_info.span,
 521                                   &format!("{} is unsafe and requires unsafe function or block \
 522                                             (error E0133)", &description.as_str()[..]),
 523                                   &details.as_str()[..]);
 524                 }
 525             }
 526         }
 527     }
 528
 529     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 530     unsafe_blocks.sort();
 531     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 532         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 533         .collect();
 534     for &(block_id, is_used) in unsafe_blocks {
 535         if !is_used {
 536             report_unused_unsafe(tcx, &used_unsafe, block_id);
 537         }
 538     }
 539 }