| use crate::MirPass; |
| use rustc_hir::def_id::DefId; |
| use rustc_index::vec::IndexVec; |
| use rustc_middle::mir::*; |
| use rustc_middle::mir::{ |
| interpret::{ConstValue, Scalar}, |
| visit::{PlaceContext, Visitor}, |
| }; |
| use rustc_middle::ty::{Ty, TyCtxt, TypeAndMut}; |
| use rustc_session::Session; |
| |
| pub struct CheckAlignment; |
| |
| impl<'tcx> MirPass<'tcx> for CheckAlignment { |
| fn is_enabled(&self, sess: &Session) -> bool { |
| sess.opts.debug_assertions |
| } |
| |
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { |
| let basic_blocks = body.basic_blocks.as_mut(); |
| let local_decls = &mut body.local_decls; |
| |
| for block in (0..basic_blocks.len()).rev() { |
| let block = block.into(); |
| for statement_index in (0..basic_blocks[block].statements.len()).rev() { |
| let location = Location { block, statement_index }; |
| let statement = &basic_blocks[block].statements[statement_index]; |
| let source_info = statement.source_info; |
| |
| let mut finder = PointerFinder { |
| local_decls, |
| tcx, |
| pointers: Vec::new(), |
| def_id: body.source.def_id(), |
| }; |
| for (pointer, pointee_ty) in finder.find_pointers(statement) { |
| debug!("Inserting alignment check for {:?}", pointer.ty(&*local_decls, tcx).ty); |
| |
| let new_block = split_block(basic_blocks, location); |
| insert_alignment_check( |
| tcx, |
| local_decls, |
| &mut basic_blocks[block], |
| pointer, |
| pointee_ty, |
| source_info, |
| new_block, |
| ); |
| } |
| } |
| } |
| } |
| } |
| |
| impl<'tcx, 'a> PointerFinder<'tcx, 'a> { |
| fn find_pointers(&mut self, statement: &Statement<'tcx>) -> Vec<(Place<'tcx>, Ty<'tcx>)> { |
| self.pointers.clear(); |
| self.visit_statement(statement, Location::START); |
| core::mem::take(&mut self.pointers) |
| } |
| } |
| |
| struct PointerFinder<'tcx, 'a> { |
| local_decls: &'a mut LocalDecls<'tcx>, |
| tcx: TyCtxt<'tcx>, |
| def_id: DefId, |
| pointers: Vec<(Place<'tcx>, Ty<'tcx>)>, |
| } |
| |
| impl<'tcx, 'a> Visitor<'tcx> for PointerFinder<'tcx, 'a> { |
| fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) { |
| if let PlaceContext::NonUse(_) = context { |
| return; |
| } |
| if !place.is_indirect() { |
| return; |
| } |
| |
| let pointer = Place::from(place.local); |
| let pointer_ty = pointer.ty(&*self.local_decls, self.tcx).ty; |
| |
| // We only want to check unsafe pointers |
| if !pointer_ty.is_unsafe_ptr() { |
| trace!("Indirect, but not an unsafe ptr, not checking {:?}", pointer_ty); |
| return; |
| } |
| |
| let Some(pointee) = pointer_ty.builtin_deref(true) else { |
| debug!("Indirect but no builtin deref: {:?}", pointer_ty); |
| return; |
| }; |
| let mut pointee_ty = pointee.ty; |
| if pointee_ty.is_array() || pointee_ty.is_slice() || pointee_ty.is_str() { |
| pointee_ty = pointee_ty.sequence_element_type(self.tcx); |
| } |
| |
| if !pointee_ty.is_sized(self.tcx, self.tcx.param_env_reveal_all_normalized(self.def_id)) { |
| debug!("Unsafe pointer, but unsized: {:?}", pointer_ty); |
| return; |
| } |
| |
| if [self.tcx.types.bool, self.tcx.types.i8, self.tcx.types.u8, self.tcx.types.str_] |
| .contains(&pointee_ty) |
| { |
| debug!("Trivially aligned pointee type: {:?}", pointer_ty); |
| return; |
| } |
| |
| self.pointers.push((pointer, pointee_ty)) |
| } |
| } |
| |
| fn split_block( |
| basic_blocks: &mut IndexVec<BasicBlock, BasicBlockData<'_>>, |
| location: Location, |
| ) -> BasicBlock { |
| let block_data = &mut basic_blocks[location.block]; |
| |
| // Drain every statement after this one and move the current terminator to a new basic block |
| let new_block = BasicBlockData { |
| statements: block_data.statements.split_off(location.statement_index), |
| terminator: block_data.terminator.take(), |
| is_cleanup: block_data.is_cleanup, |
| }; |
| |
| basic_blocks.push(new_block) |
| } |
| |
| fn insert_alignment_check<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>, |
| block_data: &mut BasicBlockData<'tcx>, |
| pointer: Place<'tcx>, |
| pointee_ty: Ty<'tcx>, |
| source_info: SourceInfo, |
| new_block: BasicBlock, |
| ) { |
| // Cast the pointer to a *const () |
| let const_raw_ptr = tcx.mk_ptr(TypeAndMut { ty: tcx.types.unit, mutbl: Mutability::Not }); |
| let rvalue = Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(pointer), const_raw_ptr); |
| let thin_ptr = local_decls.push(LocalDecl::with_source_info(const_raw_ptr, source_info)).into(); |
| block_data |
| .statements |
| .push(Statement { source_info, kind: StatementKind::Assign(Box::new((thin_ptr, rvalue))) }); |
| |
| // Transmute the pointer to a usize (equivalent to `ptr.addr()`) |
| let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize); |
| let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into(); |
| block_data |
| .statements |
| .push(Statement { source_info, kind: StatementKind::Assign(Box::new((addr, rvalue))) }); |
| |
| // Get the alignment of the pointee |
| let alignment = |
| local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into(); |
| let rvalue = Rvalue::NullaryOp(NullOp::AlignOf, pointee_ty); |
| block_data.statements.push(Statement { |
| source_info, |
| kind: StatementKind::Assign(Box::new((alignment, rvalue))), |
| }); |
| |
| // Subtract 1 from the alignment to get the alignment mask |
| let alignment_mask = |
| local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into(); |
| let one = Operand::Constant(Box::new(Constant { |
| span: source_info.span, |
| user_ty: None, |
| literal: ConstantKind::Val( |
| ConstValue::Scalar(Scalar::from_target_usize(1, &tcx)), |
| tcx.types.usize, |
| ), |
| })); |
| block_data.statements.push(Statement { |
| source_info, |
| kind: StatementKind::Assign(Box::new(( |
| alignment_mask, |
| Rvalue::BinaryOp(BinOp::Sub, Box::new((Operand::Copy(alignment), one))), |
| ))), |
| }); |
| |
| // BitAnd the alignment mask with the pointer |
| let alignment_bits = |
| local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into(); |
| block_data.statements.push(Statement { |
| source_info, |
| kind: StatementKind::Assign(Box::new(( |
| alignment_bits, |
| Rvalue::BinaryOp( |
| BinOp::BitAnd, |
| Box::new((Operand::Copy(addr), Operand::Copy(alignment_mask))), |
| ), |
| ))), |
| }); |
| |
| // Check if the alignment bits are all zero |
| let is_ok = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into(); |
| let zero = Operand::Constant(Box::new(Constant { |
| span: source_info.span, |
| user_ty: None, |
| literal: ConstantKind::Val( |
| ConstValue::Scalar(Scalar::from_target_usize(0, &tcx)), |
| tcx.types.usize, |
| ), |
| })); |
| block_data.statements.push(Statement { |
| source_info, |
| kind: StatementKind::Assign(Box::new(( |
| is_ok, |
| Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(alignment_bits), zero.clone()))), |
| ))), |
| }); |
| |
| // Set this block's terminator to our assert, continuing to new_block if we pass |
| block_data.terminator = Some(Terminator { |
| source_info, |
| kind: TerminatorKind::Assert { |
| cond: Operand::Copy(is_ok), |
| expected: true, |
| target: new_block, |
| msg: AssertKind::MisalignedPointerDereference { |
| required: Operand::Copy(alignment), |
| found: Operand::Copy(addr), |
| }, |
| unwind: UnwindAction::Terminate, |
| }, |
| }); |
| } |