diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/check_unsafety.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/check_unsafety.rs | 619 |
1 files changed, 619 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/check_unsafety.rs b/compiler/rustc_mir_transform/src/check_unsafety.rs new file mode 100644 index 000000000..d564f4801 --- /dev/null +++ b/compiler/rustc_mir_transform/src/check_unsafety.rs @@ -0,0 +1,619 @@ +use rustc_data_structures::fx::FxHashMap; +use rustc_errors::struct_span_err; +use rustc_hir as hir; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_hir::hir_id::HirId; +use rustc_hir::intravisit; +use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor}; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::{self, TyCtxt}; +use rustc_middle::{lint, mir::*}; +use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE}; +use rustc_session::lint::Level; + +use std::collections::hash_map; +use std::ops::Bound; + +pub struct UnsafetyChecker<'a, 'tcx> { + body: &'a Body<'tcx>, + body_did: LocalDefId, + violations: Vec<UnsafetyViolation>, + source_info: SourceInfo, + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + + /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint. + /// + /// The keys are the used `unsafe` blocks, the UnusedUnsafeKind indicates whether + /// or not any of the usages happen at a place that doesn't allow `unsafe_op_in_unsafe_fn`. + used_unsafe_blocks: FxHashMap<HirId, UsedUnsafeBlockData>, +} + +impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> { + fn new( + body: &'a Body<'tcx>, + body_did: LocalDefId, + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + ) -> Self { + Self { + body, + body_did, + violations: vec![], + source_info: SourceInfo::outermost(body.span), + tcx, + param_env, + used_unsafe_blocks: Default::default(), + } + } +} + +impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> { + fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) { + self.source_info = terminator.source_info; + match terminator.kind { + TerminatorKind::Goto { .. } + | TerminatorKind::SwitchInt { .. } + | TerminatorKind::Drop { .. } + | TerminatorKind::Yield { .. } + | TerminatorKind::Assert { .. } + | TerminatorKind::DropAndReplace { .. } + | TerminatorKind::GeneratorDrop + | TerminatorKind::Resume + | TerminatorKind::Abort + | TerminatorKind::Return + | TerminatorKind::Unreachable + | TerminatorKind::FalseEdge { .. } + | TerminatorKind::FalseUnwind { .. } => { + // safe (at least as emitted during MIR construction) + } + + TerminatorKind::Call { ref func, .. } => { + let func_ty = func.ty(self.body, self.tcx); + let func_id = + if let ty::FnDef(func_id, _) = func_ty.kind() { Some(func_id) } else { None }; + let sig = func_ty.fn_sig(self.tcx); + if let hir::Unsafety::Unsafe = sig.unsafety() { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::CallToUnsafeFunction, + ) + } + + if let Some(func_id) = func_id { + self.check_target_features(*func_id); + } + } + + TerminatorKind::InlineAsm { .. } => self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::UseOfInlineAssembly, + ), + } + self.super_terminator(terminator, location); + } + + fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { + self.source_info = statement.source_info; + match statement.kind { + StatementKind::Assign(..) + | StatementKind::FakeRead(..) + | StatementKind::SetDiscriminant { .. } + | StatementKind::Deinit(..) + | StatementKind::StorageLive(..) + | StatementKind::StorageDead(..) + | StatementKind::Retag { .. } + | StatementKind::AscribeUserType(..) + | StatementKind::Coverage(..) + | StatementKind::Nop => { + // safe (at least as emitted during MIR construction) + } + + StatementKind::CopyNonOverlapping(..) => unreachable!(), + } + self.super_statement(statement, location); + } + + fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { + match rvalue { + Rvalue::Aggregate(box ref aggregate, _) => match aggregate { + &AggregateKind::Array(..) | &AggregateKind::Tuple => {} + &AggregateKind::Adt(adt_did, ..) => { + match self.tcx.layout_scalar_valid_range(adt_did) { + (Bound::Unbounded, Bound::Unbounded) => {} + _ => self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::InitializingTypeWith, + ), + } + } + &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => { + let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } = + self.tcx.unsafety_check_result(def_id); + self.register_violations( + violations, + used_unsafe_blocks.iter().map(|(&h, &d)| (h, d)), + ); + } + }, + _ => {} + } + self.super_rvalue(rvalue, location); + } + + fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) { + // On types with `scalar_valid_range`, prevent + // * `&mut x.field` + // * `x.field = y;` + // * `&x.field` if `field`'s type has interior mutability + // because either of these would allow modifying the layout constrained field and + // insert values that violate the layout constraints. + if context.is_mutating_use() || context.is_borrow() { + self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use()); + } + + // Some checks below need the extra meta info of the local declaration. + let decl = &self.body.local_decls[place.local]; + + // Check the base local: it might be an unsafe-to-access static. We only check derefs of the + // temporary holding the static pointer to avoid duplicate errors + // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>. + if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) { + // If the projection root is an artificial local that we introduced when + // desugaring `static`, give a more specific error message + // (avoid the general "raw pointer" clause below, that would only be confusing). + if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info { + if self.tcx.is_mutable_static(def_id) { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::UseOfMutableStatic, + ); + return; + } else if self.tcx.is_foreign_item(def_id) { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::UseOfExternStatic, + ); + return; + } + } + } + + // Check for raw pointer `Deref`. + for (base, proj) in place.iter_projections() { + if proj == ProjectionElem::Deref { + let base_ty = base.ty(self.body, self.tcx).ty; + if base_ty.is_unsafe_ptr() { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::DerefOfRawPointer, + ) + } + } + } + + // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes + // whether we *read* the union field or potentially *write* to it (if this place is being assigned to). + let mut saw_deref = false; + for (base, proj) in place.iter_projections().rev() { + if proj == ProjectionElem::Deref { + saw_deref = true; + continue; + } + + let base_ty = base.ty(self.body, self.tcx).ty; + if base_ty.is_union() { + // If we did not hit a `Deref` yet and the overall place use is an assignment, the + // rules are different. + let assign_to_field = !saw_deref + && matches!( + context, + PlaceContext::MutatingUse( + MutatingUseContext::Store + | MutatingUseContext::Drop + | MutatingUseContext::AsmOutput + ) + ); + // If this is just an assignment, determine if the assigned type needs dropping. + if assign_to_field { + // We have to check the actual type of the assignment, as that determines if the + // old value is being dropped. + let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty; + if assigned_ty.needs_drop(self.tcx, self.param_env) { + // This would be unsafe, but should be outright impossible since we reject such unions. + self.tcx.sess.delay_span_bug( + self.source_info.span, + format!("union fields that need dropping should be impossible: {assigned_ty}") + ); + } + } else { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::AccessToUnionField, + ) + } + } + } + } +} + +impl<'tcx> UnsafetyChecker<'_, 'tcx> { + fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) { + // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such. + assert_ne!(kind, UnsafetyViolationKind::UnsafeFn); + + let source_info = self.source_info; + let lint_root = self.body.source_scopes[self.source_info.scope] + .local_data + .as_ref() + .assert_crate_local() + .lint_root; + self.register_violations( + [&UnsafetyViolation { source_info, lint_root, kind, details }], + [], + ); + } + + fn register_violations<'a>( + &mut self, + violations: impl IntoIterator<Item = &'a UnsafetyViolation>, + new_used_unsafe_blocks: impl IntoIterator<Item = (HirId, UsedUnsafeBlockData)>, + ) { + use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn}; + + let update_entry = |this: &mut Self, hir_id, new_usage| { + match this.used_unsafe_blocks.entry(hir_id) { + hash_map::Entry::Occupied(mut entry) => { + if new_usage == SomeDisallowedInUnsafeFn { + *entry.get_mut() = SomeDisallowedInUnsafeFn; + } + } + hash_map::Entry::Vacant(entry) => { + entry.insert(new_usage); + } + }; + }; + let safety = self.body.source_scopes[self.source_info.scope] + .local_data + .as_ref() + .assert_crate_local() + .safety; + match safety { + // `unsafe` blocks are required in safe code + Safety::Safe => violations.into_iter().for_each(|&violation| { + match violation.kind { + UnsafetyViolationKind::General => {} + UnsafetyViolationKind::UnsafeFn => { + bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context") + } + } + if !self.violations.contains(&violation) { + self.violations.push(violation) + } + }), + // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s + Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| { + violation.kind = UnsafetyViolationKind::UnsafeFn; + if !self.violations.contains(&violation) { + self.violations.push(violation) + } + }), + Safety::BuiltinUnsafe => {} + Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|violation| { + update_entry( + self, + hir_id, + match self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, violation.lint_root).0 + { + Level::Allow => AllAllowedInUnsafeFn(violation.lint_root), + _ => SomeDisallowedInUnsafeFn, + }, + ) + }), + }; + + new_used_unsafe_blocks + .into_iter() + .for_each(|(hir_id, usage_data)| update_entry(self, hir_id, usage_data)); + } + fn check_mut_borrowing_layout_constrained_field( + &mut self, + place: Place<'tcx>, + is_mut_use: bool, + ) { + for (place_base, elem) in place.iter_projections().rev() { + match elem { + // Modifications behind a dereference don't affect the value of + // the pointer. + ProjectionElem::Deref => return, + ProjectionElem::Field(..) => { + let ty = place_base.ty(&self.body.local_decls, self.tcx).ty; + if let ty::Adt(def, _) = ty.kind() { + if self.tcx.layout_scalar_valid_range(def.did()) + != (Bound::Unbounded, Bound::Unbounded) + { + let details = if is_mut_use { + UnsafetyViolationDetails::MutationOfLayoutConstrainedField + + // Check `is_freeze` as late as possible to avoid cycle errors + // with opaque types. + } else if !place + .ty(self.body, self.tcx) + .ty + .is_freeze(self.tcx.at(self.source_info.span), self.param_env) + { + UnsafetyViolationDetails::BorrowOfLayoutConstrainedField + } else { + continue; + }; + self.require_unsafe(UnsafetyViolationKind::General, details); + } + } + } + _ => {} + } + } + } + + /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether + /// the called function has target features the calling function hasn't. + fn check_target_features(&mut self, func_did: DefId) { + // Unsafety isn't required on wasm targets. For more information see + // the corresponding check in typeck/src/collect.rs + if self.tcx.sess.target.options.is_like_wasm { + return; + } + + let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features; + // The body might be a constant, so it doesn't have codegen attributes. + let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features; + + // Is `callee_features` a subset of `calling_features`? + if !callee_features.iter().all(|feature| self_features.contains(feature)) { + self.require_unsafe( + UnsafetyViolationKind::General, + UnsafetyViolationDetails::CallToFunctionWith, + ) + } + } +} + +pub(crate) fn provide(providers: &mut Providers) { + *providers = Providers { + unsafety_check_result: |tcx, def_id| { + if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) { + tcx.unsafety_check_result_for_const_arg(def) + } else { + unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id)) + } + }, + unsafety_check_result_for_const_arg: |tcx, (did, param_did)| { + unsafety_check_result( + tcx, + ty::WithOptConstParam { did, const_param_did: Some(param_did) }, + ) + }, + ..*providers + }; +} + +/// Context information for [`UnusedUnsafeVisitor`] traversal, +/// saves (innermost) relevant context +#[derive(Copy, Clone, Debug)] +enum Context { + Safe, + /// in an `unsafe fn` + UnsafeFn(HirId), + /// in a *used* `unsafe` block + /// (i.e. a block without unused-unsafe warning) + UnsafeBlock(HirId), +} + +struct UnusedUnsafeVisitor<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + used_unsafe_blocks: &'a FxHashMap<HirId, UsedUnsafeBlockData>, + context: Context, + unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>, +} + +impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> { + fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) { + use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn}; + + if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules { + let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) { + (Level::Allow, _) => Some(SomeDisallowedInUnsafeFn), + _ => self.used_unsafe_blocks.get(&block.hir_id).copied(), + }; + let unused_unsafe = match (self.context, used) { + (_, None) => UnusedUnsafe::Unused, + (Context::Safe, Some(_)) + | (Context::UnsafeFn(_), Some(SomeDisallowedInUnsafeFn)) => { + let previous_context = self.context; + self.context = Context::UnsafeBlock(block.hir_id); + intravisit::walk_block(self, block); + self.context = previous_context; + return; + } + (Context::UnsafeFn(hir_id), Some(AllAllowedInUnsafeFn(lint_root))) => { + UnusedUnsafe::InUnsafeFn(hir_id, lint_root) + } + (Context::UnsafeBlock(hir_id), Some(_)) => UnusedUnsafe::InUnsafeBlock(hir_id), + }; + self.unused_unsafes.push((block.hir_id, unused_unsafe)); + } + intravisit::walk_block(self, block); + } + + fn visit_fn( + &mut self, + fk: intravisit::FnKind<'tcx>, + _fd: &'tcx hir::FnDecl<'tcx>, + b: hir::BodyId, + _s: rustc_span::Span, + _id: HirId, + ) { + if matches!(fk, intravisit::FnKind::Closure) { + self.visit_body(self.tcx.hir().body(b)) + } + } +} + +fn check_unused_unsafe( + tcx: TyCtxt<'_>, + def_id: LocalDefId, + used_unsafe_blocks: &FxHashMap<HirId, UsedUnsafeBlockData>, +) -> Vec<(HirId, UnusedUnsafe)> { + let body_id = tcx.hir().maybe_body_owned_by(def_id); + + let Some(body_id) = body_id else { + debug!("check_unused_unsafe({:?}) - no body found", def_id); + return vec![]; + }; + + let body = tcx.hir().body(body_id); + let hir_id = tcx.hir().local_def_id_to_hir_id(def_id); + let context = match tcx.hir().fn_sig_by_hir_id(hir_id) { + Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id), + _ => Context::Safe, + }; + + debug!( + "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})", + def_id, body, context, used_unsafe_blocks + ); + + let mut unused_unsafes = vec![]; + + let mut visitor = UnusedUnsafeVisitor { + tcx, + used_unsafe_blocks, + context, + unused_unsafes: &mut unused_unsafes, + }; + intravisit::Visitor::visit_body(&mut visitor, body); + + unused_unsafes +} + +fn unsafety_check_result<'tcx>( + tcx: TyCtxt<'tcx>, + def: ty::WithOptConstParam<LocalDefId>, +) -> &'tcx UnsafetyCheckResult { + debug!("unsafety_violations({:?})", def); + + // N.B., this borrow is valid because all the consumers of + // `mir_built` force this. + let body = &tcx.mir_built(def).borrow(); + + let param_env = tcx.param_env(def.did); + + let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env); + checker.visit_body(&body); + + let unused_unsafes = (!tcx.is_closure(def.did.to_def_id())) + .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks)); + + tcx.arena.alloc(UnsafetyCheckResult { + violations: checker.violations, + used_unsafe_blocks: checker.used_unsafe_blocks, + unused_unsafes, + }) +} + +fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) { + let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id)); + tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| { + let msg = "unnecessary `unsafe` block"; + let mut db = lint.build(msg); + db.span_label(span, msg); + match kind { + UnusedUnsafe::Unused => {} + UnusedUnsafe::InUnsafeBlock(id) => { + db.span_label( + tcx.sess.source_map().guess_head_span(tcx.hir().span(id)), + "because it's nested under this `unsafe` block", + ); + } + UnusedUnsafe::InUnsafeFn(id, usage_lint_root) => { + db.span_label( + tcx.sess.source_map().guess_head_span(tcx.hir().span(id)), + "because it's nested under this `unsafe` fn", + ) + .note( + "this `unsafe` block does contain unsafe operations, \ + but those are already allowed in an `unsafe fn`", + ); + let (level, source) = + tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root); + assert_eq!(level, Level::Allow); + lint::explain_lint_level_source( + UNSAFE_OP_IN_UNSAFE_FN, + Level::Allow, + source, + &mut db, + ); + } + } + + db.emit(); + }); +} + +pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) { + debug!("check_unsafety({:?})", def_id); + + // closures are handled by their parent fn. + if tcx.is_closure(def_id.to_def_id()) { + return; + } + + let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id); + + for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() { + let (description, note) = details.description_and_note(); + + // Report an error. + let unsafe_fn_msg = + if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" }; + + match kind { + UnsafetyViolationKind::General => { + // once + struct_span_err!( + tcx.sess, + source_info.span, + E0133, + "{} is unsafe and requires unsafe{} block", + description, + unsafe_fn_msg, + ) + .span_label(source_info.span, description) + .note(note) + .emit(); + } + UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir( + UNSAFE_OP_IN_UNSAFE_FN, + lint_root, + source_info.span, + |lint| { + lint.build(&format!( + "{} is unsafe and requires unsafe block (error E0133)", + description, + )) + .span_label(source_info.span, description) + .note(note) + .emit(); + }, + ), + } + } + + for &(block_id, kind) in unused_unsafes.as_ref().unwrap() { + report_unused_unsafe(tcx, kind, block_id); + } +} + +fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool { + tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow +} |