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::maps::Providers;
  16 use rustc::ty::{self, TyCtxt};
  17 use rustc::hir;
  18 use rustc::hir::def_id::DefId;
  19 use rustc::lint::builtin::{SAFE_EXTERN_STATICS, SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
  20 use rustc::mir::*;
  21 use rustc::mir::visit::{PlaceContext, Visitor};
  22
  23 use syntax::ast;
  24 use syntax::symbol::Symbol;
  25
  26 use util;
  27
  28 pub struct UnsafetyChecker<'a, 'tcx: 'a> {
  29     mir: &'a Mir<'tcx>,
  30     visibility_scope_info: &'a IndexVec<VisibilityScope, VisibilityScopeInfo>,
  31     violations: Vec<UnsafetyViolation>,
  32     source_info: SourceInfo,
  33     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  34     param_env: ty::ParamEnv<'tcx>,
  35     used_unsafe: FxHashSet<ast::NodeId>,
  36     inherited_blocks: Vec<(ast::NodeId, bool)>,
  37 }
  38
  39 impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
  40     fn new(mir: &'a Mir<'tcx>,
  41            visibility_scope_info: &'a IndexVec<VisibilityScope, VisibilityScopeInfo>,
  42            tcx: TyCtxt<'a, 'tcx, 'tcx>,
  43            param_env: ty::ParamEnv<'tcx>) -> Self {
  44         Self {
  45             mir,
  46             visibility_scope_info,
  47             violations: vec![],
  48             source_info: SourceInfo {
  49                 span: mir.span,
  50                 scope: ARGUMENT_VISIBILITY_SCOPE
  51             },
  52             tcx,
  53             param_env,
  54             used_unsafe: FxHashSet(),
  55             inherited_blocks: vec![],
  56         }
  57     }
  58 }
  59
  60 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  61     fn visit_terminator(&mut self,
  62                         block: BasicBlock,
  63                         terminator: &Terminator<'tcx>,
  64                         location: Location)
  65     {
  66         self.source_info = terminator.source_info;
  67         match terminator.kind {
  68             TerminatorKind::Goto { .. } |
  69             TerminatorKind::SwitchInt { .. } |
  70             TerminatorKind::Drop { .. } |
  71             TerminatorKind::Yield { .. } |
  72             TerminatorKind::Assert { .. } |
  73             TerminatorKind::DropAndReplace { .. } |
  74             TerminatorKind::GeneratorDrop |
  75             TerminatorKind::Resume |
  76             TerminatorKind::Abort |
  77             TerminatorKind::Return |
  78             TerminatorKind::Unreachable |
  79             TerminatorKind::FalseEdges { .. } |
  80             TerminatorKind::FalseUnwind { .. } => {
  81                 // safe (at least as emitted during MIR construction)
  82             }
  83
  84             TerminatorKind::Call { ref func, .. } => {
  85                 let func_ty = func.ty(self.mir, self.tcx);
  86                 let sig = func_ty.fn_sig(self.tcx);
  87                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  88                     self.require_unsafe("call to unsafe function")
  89                 }
  90             }
  91         }
  92         self.super_terminator(block, terminator, location);
  93     }
  94
  95     fn visit_statement(&mut self,
  96                        block: BasicBlock,
  97                        statement: &Statement<'tcx>,
  98                        location: Location)
  99     {
 100         self.source_info = statement.source_info;
 101         match statement.kind {
 102             StatementKind::Assign(..) |
 103             StatementKind::SetDiscriminant { .. } |
 104             StatementKind::StorageLive(..) |
 105             StatementKind::StorageDead(..) |
 106             StatementKind::EndRegion(..) |
 107             StatementKind::Validate(..) |
 108             StatementKind::UserAssertTy(..) |
 109             StatementKind::Nop => {
 110                 // safe (at least as emitted during MIR construction)
 111             }
 112
 113             StatementKind::InlineAsm { .. } => {
 114                 self.require_unsafe("use of inline assembly")
 115             },
 116         }
 117         self.super_statement(block, statement, location);
 118     }
 119
 120     fn visit_rvalue(&mut self,
 121                     rvalue: &Rvalue<'tcx>,
 122                     location: Location)
 123     {
 124         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 125             match aggregate {
 126                 &AggregateKind::Array(..) |
 127                 &AggregateKind::Tuple |
 128                 &AggregateKind::Adt(..) => {}
 129                 &AggregateKind::Closure(def_id, _) |
 130                 &AggregateKind::Generator(def_id, _, _) => {
 131                     let UnsafetyCheckResult {
 132                         violations, unsafe_blocks
 133                     } = self.tcx.unsafety_check_result(def_id);
 134                     self.register_violations(&violations, &unsafe_blocks);
 135                 }
 136             }
 137         }
 138         self.super_rvalue(rvalue, location);
 139     }
 140
 141     fn visit_place(&mut self,
 142                     place: &Place<'tcx>,
 143                     context: PlaceContext<'tcx>,
 144                     location: Location) {
 145         if let PlaceContext::Borrow { .. } = context {
 146             if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 147                 let source_info = self.source_info;
 148                 let lint_root =
 149                     self.visibility_scope_info[source_info.scope].lint_root;
 150                 self.register_violations(&[UnsafetyViolation {
 151                     source_info,
 152                     description: Symbol::intern("borrow of packed field").as_interned_str(),
 153                     kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 154                 }], &[]);
 155             }
 156         }
 157
 158         match place {
 159             &Place::Projection(box Projection {
 160                 ref base, ref elem
 161             }) => {
 162                 let old_source_info = self.source_info;
 163                 if let &Place::Local(local) = base {
 164                     if self.mir.local_decls[local].internal {
 165                         // Internal locals are used in the `move_val_init` desugaring.
 166                         // We want to check unsafety against the source info of the
 167                         // desugaring, rather than the source info of the RHS.
 168                         self.source_info = self.mir.local_decls[local].source_info;
 169                     }
 170                 }
 171                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 172                 match base_ty.sty {
 173                     ty::TyRawPtr(..) => {
 174                         self.require_unsafe("dereference of raw pointer")
 175                     }
 176                     ty::TyAdt(adt, _) => {
 177                         if adt.is_union() {
 178                             if context == PlaceContext::Store ||
 179                                 context == PlaceContext::AsmOutput ||
 180                                 context == PlaceContext::Drop
 181                             {
 182                                 let elem_ty = match elem {
 183                                     &ProjectionElem::Field(_, ty) => ty,
 184                                     _ => span_bug!(
 185                                         self.source_info.span,
 186                                         "non-field projection {:?} from union?",
 187                                         place)
 188                                 };
 189                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 190                                                             self.source_info.span) {
 191                                     self.require_unsafe(
 192                                         "assignment to non-`Copy` union field")
 193                                 } else {
 194                                     // write to non-move union, safe
 195                                 }
 196                             } else {
 197                                 self.require_unsafe("access to union field")
 198                             }
 199                         }
 200                     }
 201                     _ => {}
 202                 }
 203                 self.source_info = old_source_info;
 204             }
 205             &Place::Local(..) => {
 206                 // locals are safe
 207             }
 208             &Place::Static(box Static { def_id, ty: _ }) => {
 209                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 210                     self.require_unsafe("use of mutable static");
 211                 } else if self.tcx.is_foreign_item(def_id) {
 212                     let source_info = self.source_info;
 213                     let lint_root =
 214                         self.visibility_scope_info[source_info.scope].lint_root;
 215                     self.register_violations(&[UnsafetyViolation {
 216                         source_info,
 217                         description: Symbol::intern("use of extern static").as_interned_str(),
 218                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 219                     }], &[]);
 220                 }
 221             }
 222         };
 223         self.super_place(place, context, location);
 224     }
 225 }
 226
 227 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 228     fn require_unsafe(&mut self,
 229                       description: &'static str)
 230     {
 231         let source_info = self.source_info;
 232         self.register_violations(&[UnsafetyViolation {
 233             source_info,
 234             description: Symbol::intern(description).as_interned_str(),
 235             kind: UnsafetyViolationKind::General,
 236         }], &[]);
 237     }
 238
 239     fn register_violations(&mut self,
 240                            violations: &[UnsafetyViolation],
 241                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 242         let within_unsafe = match self.visibility_scope_info[self.source_info.scope].safety {
 243             Safety::Safe => {
 244                 for violation in violations {
 245                     if !self.violations.contains(violation) {
 246                         self.violations.push(violation.clone())
 247                     }
 248                 }
 249
 250                 false
 251             }
 252             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 253             Safety::ExplicitUnsafe(node_id) => {
 254                 if !violations.is_empty() {
 255                     self.used_unsafe.insert(node_id);
 256                 }
 257                 true
 258             }
 259         };
 260         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 261             (node_id, is_used && !within_unsafe)
 262         }));
 263     }
 264 }
 265
 266 pub(crate) fn provide(providers: &mut Providers) {
 267     *providers = Providers {
 268         unsafety_check_result,
 269         unsafe_derive_on_repr_packed,
 270         ..*providers
 271     };
 272 }
 273
 274 struct UnusedUnsafeVisitor<'a> {
 275     used_unsafe: &'a FxHashSet<ast::NodeId>,
 276     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 277 }
 278
 279 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 280     fn nested_visit_map<'this>(&'this mut self) ->
 281         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 282     {
 283         hir::intravisit::NestedVisitorMap::None
 284     }
 285
 286     fn visit_block(&mut self, block: &'tcx hir::Block) {
 287         hir::intravisit::walk_block(self, block);
 288
 289         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 290             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 291         }
 292     }
 293 }
 294
 295 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 296                                  def_id: DefId,
 297                                  used_unsafe: &FxHashSet<ast::NodeId>,
 298                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 299 {
 300     let body_id =
 301         tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
 302             tcx.hir.maybe_body_owned_by(node_id)
 303         });
 304
 305     let body_id = match body_id {
 306         Some(body) => body,
 307         None => {
 308             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 309             return
 310         }
 311     };
 312     let body = tcx.hir.body(body_id);
 313     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 314            def_id, body, used_unsafe);
 315
 316     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 317     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 318 }
 319
 320 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 321                                    -> UnsafetyCheckResult
 322 {
 323     debug!("unsafety_violations({:?})", def_id);
 324
 325     // NB: this borrow is valid because all the consumers of
 326     // `mir_built` force this.
 327     let mir = &tcx.mir_built(def_id).borrow();
 328
 329     let visibility_scope_info = match mir.visibility_scope_info {
 330         ClearCrossCrate::Set(ref data) => data,
 331         ClearCrossCrate::Clear => {
 332             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 333             return UnsafetyCheckResult {
 334                 violations: Lrc::new([]),
 335                 unsafe_blocks: Lrc::new([])
 336             }
 337         }
 338     };
 339
 340     let param_env = tcx.param_env(def_id);
 341     let mut checker = UnsafetyChecker::new(
 342         mir, visibility_scope_info, tcx, param_env);
 343     checker.visit_mir(mir);
 344
 345     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 346     UnsafetyCheckResult {
 347         violations: checker.violations.into(),
 348         unsafe_blocks: checker.inherited_blocks.into()
 349     }
 350 }
 351
 352 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 353     let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
 354         Some(node_id) => node_id,
 355         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 356     };
 357
 358     // FIXME: when we make this a hard error, this should have its
 359     // own error code.
 360     let message = if !tcx.generics_of(def_id).types.is_empty() {
 361         format!("#[derive] can't be used on a #[repr(packed)] struct with \
 362                  type parameters (error E0133)")
 363     } else {
 364         format!("#[derive] can't be used on a non-Copy #[repr(packed)] struct \
 365                  (error E0133)")
 366     };
 367     tcx.lint_node(SAFE_PACKED_BORROWS,
 368                   lint_node_id,
 369                   tcx.def_span(def_id),
 370                   &message);
 371 }
 372
 373 /// Return the NodeId for an enclosing scope that is also `unsafe`
 374 fn is_enclosed(tcx: TyCtxt,
 375                used_unsafe: &FxHashSet<ast::NodeId>,
 376                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 377     let parent_id = tcx.hir.get_parent_node(id);
 378     if parent_id != id {
 379         if used_unsafe.contains(&parent_id) {
 380             Some(("block".to_string(), parent_id))
 381         } else if let Some(hir::map::NodeItem(&hir::Item {
 382             node: hir::ItemFn(_, fn_unsafety, _, _, _, _),
 383             ..
 384         })) = tcx.hir.find(parent_id) {
 385             match fn_unsafety {
 386                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 387                 hir::Unsafety::Normal => None,
 388             }
 389         } else {
 390             is_enclosed(tcx, used_unsafe, parent_id)
 391         }
 392     } else {
 393         None
 394     }
 395 }
 396
 397 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 398     let span = tcx.sess.codemap().def_span(tcx.hir.span(id));
 399     let msg = "unnecessary `unsafe` block";
 400     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 401     db.span_label(span, msg);
 402     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 403         db.span_label(tcx.sess.codemap().def_span(tcx.hir.span(id)),
 404                       format!("because it's nested under this `unsafe` {}", kind));
 405     }
 406     db.emit();
 407 }
 408
 409 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 410     debug!("builtin_derive_def_id({:?})", def_id);
 411     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 412         if tcx.has_attr(impl_def_id, "automatically_derived") {
 413             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 414             Some(impl_def_id)
 415         } else {
 416             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 417             None
 418         }
 419     } else {
 420         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 421         None
 422     }
 423 }
 424
 425 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 426     debug!("check_unsafety({:?})", def_id);
 427
 428     // closures are handled by their parent fn.
 429     if tcx.is_closure(def_id) {
 430         return;
 431     }
 432
 433     let UnsafetyCheckResult {
 434         violations,
 435         unsafe_blocks
 436     } = tcx.unsafety_check_result(def_id);
 437
 438     for &UnsafetyViolation {
 439         source_info, description, kind
 440     } in violations.iter() {
 441         // Report an error.
 442         match kind {
 443             UnsafetyViolationKind::General => {
 444                 struct_span_err!(
 445                     tcx.sess, source_info.span, E0133,
 446                     "{} requires unsafe function or block", description)
 447                     .span_label(source_info.span, &description.as_str()[..])
 448                     .emit();
 449             }
 450             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 451                 tcx.lint_node(SAFE_EXTERN_STATICS,
 452                               lint_node_id,
 453                               source_info.span,
 454                               &format!("{} requires unsafe function or \
 455                                         block (error E0133)", &description.as_str()[..]));
 456             }
 457             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 458                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 459                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 460                 } else {
 461                     tcx.lint_node(SAFE_PACKED_BORROWS,
 462                                   lint_node_id,
 463                                   source_info.span,
 464                                   &format!("{} requires unsafe function or \
 465                                             block (error E0133)", &description.as_str()[..]));
 466                 }
 467             }
 468         }
 469     }
 470
 471     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 472     unsafe_blocks.sort();
 473     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 474         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 475         .collect();
 476     for &(block_id, is_used) in unsafe_blocks {
 477         if !is_used {
 478             report_unused_unsafe(tcx, &used_unsafe, block_id);
 479         }
 480     }
 481 }