1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
|
use crate::MirPass;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_index::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>) {
// This pass emits new panics. If for whatever reason we do not have a panic
// implementation, running this pass may cause otherwise-valid code to not compile.
if tcx.lang_items().get(LangItem::PanicImpl).is_none() {
return;
}
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: Box::new(AssertKind::MisalignedPointerDereference {
required: Operand::Copy(alignment),
found: Operand::Copy(addr),
}),
unwind: UnwindAction::Terminate,
},
});
}
|
