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Rollup merge of #72525 - RalfJung:miri-cast-checks, r=eddyb

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Miri casts: do not blindly rely on dest type

Make sure that we notice when the MIR is bad and the casted-to and destination type are e.g. of different size, as suggested by @eddyb.
This commit is contained in:
Ralf Jung 2020-05-25 11:01:05 +02:00 committed by GitHub
commit 4a5a6559d3
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2 changed files with 101 additions and 94 deletions
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190
src/librustc_mir/interpret/cast.rs
View File

@ -1,36 +1,47 @@
use std::convert::TryFrom;
use super::{FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy};
use rustc_apfloat::ieee::{Double, Single};
use rustc_apfloat::{Float, FloatConvert};
use rustc_ast::ast::FloatTy;
use rustc_attr as attr;
use rustc_middle::mir::interpret::{InterpResult, PointerArithmetic, Scalar};
use rustc_middle::mir::CastKind;
use rustc_middle::ty::adjustment::PointerCast;
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
use rustc_middle::ty::{self, Ty, TypeAndMut, TypeFoldable};
use rustc_span::symbol::sym;
use rustc_target::abi::{LayoutOf, Size, Variants};
use rustc_target::abi::{Integer, LayoutOf, Variants};
use super::{truncate, FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy};
impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
pub fn cast(
&mut self,
src: OpTy<'tcx, M::PointerTag>,
kind: CastKind,
cast_kind: CastKind,
cast_ty: Ty<'tcx>,
dest: PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
use rustc_middle::mir::CastKind::*;
match kind {
// FIXME: In which cases should we trigger UB when the source is uninit?
match cast_kind {
Pointer(PointerCast::Unsize) => {
self.unsize_into(src, dest)?;
let cast_ty = self.layout_of(cast_ty)?;
self.unsize_into(src, cast_ty, dest)?;
}
Misc | Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer) => {
Misc => {
let src = self.read_immediate(src)?;
let res = self.cast_immediate(src, dest.layout)?;
let res = self.misc_cast(src, cast_ty)?;
self.write_immediate(res, dest)?;
}
Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer) => {
// These are NOPs, but can be wide pointers.
let v = self.read_immediate(src)?;
self.write_immediate(*v, dest)?;
}
Pointer(PointerCast::ReifyFnPointer) => {
// The src operand does not matter, just its type
match src.layout.ty.kind {
@ -61,12 +72,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Pointer(PointerCast::UnsafeFnPointer) => {
let src = self.read_immediate(src)?;
match dest.layout.ty.kind {
match cast_ty.kind {
ty::FnPtr(_) => {
// No change to value
self.write_immediate(*src, dest)?;
}
_ => bug!("fn to unsafe fn cast on {:?}", dest.layout.ty),
_ => bug!("fn to unsafe fn cast on {:?}", cast_ty),
}
}
@ -95,25 +106,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Ok(())
}
fn cast_immediate(
fn misc_cast(
&self,
src: ImmTy<'tcx, M::PointerTag>,
dest_layout: TyAndLayout<'tcx>,
cast_ty: Ty<'tcx>,
) -> InterpResult<'tcx, Immediate<M::PointerTag>> {
use rustc_middle::ty::TyKind::*;
trace!("Casting {:?}: {:?} to {:?}", *src, src.layout.ty, dest_layout.ty);
trace!("Casting {:?}: {:?} to {:?}", *src, src.layout.ty, cast_ty);
match src.layout.ty.kind {
// Floating point
Float(FloatTy::F32) => {
return Ok(self
.cast_from_float(src.to_scalar()?.to_f32()?, dest_layout.ty)?
.into());
return Ok(self.cast_from_float(src.to_scalar()?.to_f32()?, cast_ty).into());
}
Float(FloatTy::F64) => {
return Ok(self
.cast_from_float(src.to_scalar()?.to_f64()?, dest_layout.ty)?
.into());
return Ok(self.cast_from_float(src.to_scalar()?.to_f64()?, cast_ty).into());
}
// The rest is integer/pointer-"like", including fn ptr casts and casts from enums that
// are represented as integers.
@ -128,95 +135,92 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
),
}
// # First handle non-scalar source values.
// Handle cast from a univariant (ZST) enum.
match src.layout.variants {
Variants::Single { index } => {
if let Some(discr) = src.layout.ty.discriminant_for_variant(*self.tcx, index) {
assert!(src.layout.is_zst());
let discr_layout = self.layout_of(discr.ty)?;
return Ok(self
.cast_from_int_like(discr.val, discr_layout, dest_layout)?
.into());
return Ok(self.cast_from_scalar(discr.val, discr_layout, cast_ty).into());
}
}
Variants::Multiple { .. } => {}
}
// Handle casting the metadata away from a fat pointer.
if src.layout.ty.is_unsafe_ptr()
&& dest_layout.ty.is_unsafe_ptr()
&& dest_layout.size != src.layout.size
{
assert_eq!(src.layout.size, 2 * self.memory.pointer_size());
assert_eq!(dest_layout.size, self.memory.pointer_size());
assert!(dest_layout.ty.is_unsafe_ptr());
match *src {
Immediate::ScalarPair(data, _) => return Ok(data.into()),
Immediate::Scalar(..) => bug!(
"{:?} input to a fat-to-thin cast ({:?} -> {:?})",
*src,
src.layout.ty,
dest_layout.ty
),
};
// Handle casting any ptr to raw ptr (might be a fat ptr).
if src.layout.ty.is_any_ptr() && cast_ty.is_unsafe_ptr() {
let dest_layout = self.layout_of(cast_ty)?;
if dest_layout.size == src.layout.size {
// Thin or fat pointer that just hast the ptr kind of target type changed.
return Ok(*src);
} else {
// Casting the metadata away from a fat ptr.
assert_eq!(src.layout.size, 2 * self.memory.pointer_size());
assert_eq!(dest_layout.size, self.memory.pointer_size());
assert!(src.layout.ty.is_unsafe_ptr());
return match *src {
Immediate::ScalarPair(data, _) => Ok(data.into()),
Immediate::Scalar(..) => bug!(
"{:?} input to a fat-to-thin cast ({:?} -> {:?})",
*src,
src.layout.ty,
cast_ty
),
};
}
}
// Handle casting any ptr to raw ptr (might be a fat ptr).
if src.layout.ty.is_any_ptr() && dest_layout.ty.is_unsafe_ptr() {
// The only possible size-unequal case was handled above.
assert_eq!(src.layout.size, dest_layout.size);
return Ok(*src);
}
// # The remaining source values are scalar.
// For all remaining casts, we either
// (a) cast a raw ptr to usize, or
// (b) cast from an integer-like (including bool, char, enums).
// In both cases we want the bits.
let bits = self.force_bits(src.to_scalar()?, src.layout.size)?;
Ok(self.cast_from_int_like(bits, src.layout, dest_layout)?.into())
Ok(self.cast_from_scalar(bits, src.layout, cast_ty).into())
}
fn cast_from_int_like(
pub(super) fn cast_from_scalar(
&self,
v: u128, // raw bits
v: u128, // raw bits (there is no ScalarTy so we separate data+layout)
src_layout: TyAndLayout<'tcx>,
dest_layout: TyAndLayout<'tcx>,
) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
cast_ty: Ty<'tcx>,
) -> Scalar<M::PointerTag> {
// Let's make sure v is sign-extended *if* it has a signed type.
let signed = src_layout.abi.is_signed();
let signed = src_layout.abi.is_signed(); // Also asserts that abi is `Scalar`.
let v = if signed { self.sign_extend(v, src_layout) } else { v };
trace!("cast_from_int: {}, {}, {}", v, src_layout.ty, dest_layout.ty);
trace!("cast_from_scalar: {}, {} -> {}", v, src_layout.ty, cast_ty);
use rustc_middle::ty::TyKind::*;
match dest_layout.ty.kind {
match cast_ty.kind {
Int(_) | Uint(_) | RawPtr(_) => {
let v = self.truncate(v, dest_layout);
Ok(Scalar::from_uint(v, dest_layout.size))
let size = match cast_ty.kind {
Int(t) => Integer::from_attr(self, attr::IntType::SignedInt(t)).size(),
Uint(t) => Integer::from_attr(self, attr::IntType::UnsignedInt(t)).size(),
RawPtr(_) => self.pointer_size(),
_ => bug!(),
};
let v = truncate(v, size);
Scalar::from_uint(v, size)
}
Float(FloatTy::F32) if signed => {
Ok(Scalar::from_f32(Single::from_i128(v as i128).value))
}
Float(FloatTy::F64) if signed => {
Ok(Scalar::from_f64(Double::from_i128(v as i128).value))
}
Float(FloatTy::F32) => Ok(Scalar::from_f32(Single::from_u128(v).value)),
Float(FloatTy::F64) => Ok(Scalar::from_f64(Double::from_u128(v).value)),
Float(FloatTy::F32) if signed => Scalar::from_f32(Single::from_i128(v as i128).value),
Float(FloatTy::F64) if signed => Scalar::from_f64(Double::from_i128(v as i128).value),
Float(FloatTy::F32) => Scalar::from_f32(Single::from_u128(v).value),
Float(FloatTy::F64) => Scalar::from_f64(Double::from_u128(v).value),
Char => {
// `u8` to `char` cast
Ok(Scalar::from_u32(u8::try_from(v).unwrap().into()))
Scalar::from_u32(u8::try_from(v).unwrap().into())
}
// Casts to bool are not permitted by rustc, no need to handle them here.
_ => bug!("invalid int to {:?} cast", dest_layout.ty),
_ => bug!("invalid int to {:?} cast", cast_ty),
}
}
fn cast_from_float<F>(
&self,
f: F,
dest_ty: Ty<'tcx>,
) -> InterpResult<'tcx, Scalar<M::PointerTag>>
fn cast_from_float<F>(&self, f: F, dest_ty: Ty<'tcx>) -> Scalar<M::PointerTag>
where
F: Float + Into<Scalar<M::PointerTag>> + FloatConvert<Single> + FloatConvert<Double>,
{
@ -224,25 +228,25 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
match dest_ty.kind {
// float -> uint
Uint(t) => {
let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits());
let size = Integer::from_attr(self, attr::IntType::UnsignedInt(t)).size();
// `to_u128` is a saturating cast, which is what we need
// (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
let v = f.to_u128(usize::try_from(width).unwrap()).value;
let v = f.to_u128(size.bits_usize()).value;
// This should already fit the bit width
Ok(Scalar::from_uint(v, Size::from_bits(width)))
Scalar::from_uint(v, size)
}
// float -> int
Int(t) => {
let width = t.bit_width().unwrap_or_else(|| self.pointer_size().bits());
let size = Integer::from_attr(self, attr::IntType::SignedInt(t)).size();
// `to_i128` is a saturating cast, which is what we need
// (https://doc.rust-lang.org/nightly/nightly-rustc/rustc_apfloat/trait.Float.html#method.to_i128_r).
let v = f.to_i128(usize::try_from(width).unwrap()).value;
Ok(Scalar::from_int(v, Size::from_bits(width)))
let v = f.to_i128(size.bits_usize()).value;
Scalar::from_int(v, size)
}
// float -> f32
Float(FloatTy::F32) => Ok(Scalar::from_f32(f.convert(&mut false).value)),
Float(FloatTy::F32) => Scalar::from_f32(f.convert(&mut false).value),
// float -> f64
Float(FloatTy::F64) => Ok(Scalar::from_f64(f.convert(&mut false).value)),
Float(FloatTy::F64) => Scalar::from_f64(f.convert(&mut false).value),
// That's it.
_ => bug!("invalid float to {:?} cast", dest_ty),
}
@ -254,11 +258,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
dest: PlaceTy<'tcx, M::PointerTag>,
// The pointee types
source_ty: Ty<'tcx>,
dest_ty: Ty<'tcx>,
cast_ty: Ty<'tcx>,
) -> InterpResult<'tcx> {
// A<Struct> -> A<Trait> conversion
let (src_pointee_ty, dest_pointee_ty) =
self.tcx.struct_lockstep_tails_erasing_lifetimes(source_ty, dest_ty, self.param_env);
self.tcx.struct_lockstep_tails_erasing_lifetimes(source_ty, cast_ty, self.param_env);
match (&src_pointee_ty.kind, &dest_pointee_ty.kind) {
(&ty::Array(_, length), &ty::Slice(_)) => {
@ -286,32 +290,33 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.write_immediate(val, dest)
}
_ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, dest.layout.ty),
_ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, cast_ty),
}
}
fn unsize_into(
&mut self,
src: OpTy<'tcx, M::PointerTag>,
cast_ty: TyAndLayout<'tcx>,
dest: PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
trace!("Unsizing {:?} into {:?}", src, dest);
match (&src.layout.ty.kind, &dest.layout.ty.kind) {
(&ty::Ref(_, s, _), &ty::Ref(_, d, _) | &ty::RawPtr(TypeAndMut { ty: d, .. }))
| (&ty::RawPtr(TypeAndMut { ty: s, .. }), &ty::RawPtr(TypeAndMut { ty: d, .. })) => {
self.unsize_into_ptr(src, dest, s, d)
trace!("Unsizing {:?} of type {} into {:?}", *src, src.layout.ty, cast_ty.ty);
match (&src.layout.ty.kind, &cast_ty.ty.kind) {
(&ty::Ref(_, s, _), &ty::Ref(_, c, _) | &ty::RawPtr(TypeAndMut { ty: c, .. }))
| (&ty::RawPtr(TypeAndMut { ty: s, .. }), &ty::RawPtr(TypeAndMut { ty: c, .. })) => {
self.unsize_into_ptr(src, dest, s, c)
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
if def_a.is_box() || def_b.is_box() {
if !def_a.is_box() || !def_b.is_box() {
bug!("invalid unsizing between {:?} -> {:?}", src.layout, dest.layout);
bug!("invalid unsizing between {:?} -> {:?}", src.layout.ty, cast_ty.ty);
}
return self.unsize_into_ptr(
src,
dest,
src.layout.ty.boxed_ty(),
dest.layout.ty.boxed_ty(),
cast_ty.ty.boxed_ty(),
);
}
@ -319,15 +324,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// Example: `Arc<T>` -> `Arc<Trait>`
// here we need to increase the size of every &T thin ptr field to a fat ptr
for i in 0..src.layout.fields.count() {
let dst_field = self.place_field(dest, i)?;
if dst_field.layout.is_zst() {
let cast_ty_field = cast_ty.field(self, i)?;
if cast_ty_field.is_zst() {
continue;
}
let src_field = self.operand_field(src, i)?;
if src_field.layout.ty == dst_field.layout.ty {
let dst_field = self.place_field(dest, i)?;
if src_field.layout.ty == cast_ty_field.ty {
self.copy_op(src_field, dst_field)?;
} else {
self.unsize_into(src_field, dst_field)?;
self.unsize_into(src_field, cast_ty_field, dst_field)?;
}
}
Ok(())

5
src/librustc_mir/interpret/step.rs
View File

@ -253,9 +253,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), dest)?;
}
Cast(kind, ref operand, _) => {
Cast(cast_kind, ref operand, cast_ty) => {
let src = self.eval_operand(operand, None)?;
self.cast(src, kind, dest)?;
let cast_ty = self.subst_from_current_frame_and_normalize_erasing_regions(cast_ty);
self.cast(src, cast_kind, cast_ty, dest)?;
}
Discriminant(place) => {