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Miri casts: do not blindly rely on dest type
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@RalfJung
RalfJung committed May 24, 2020
1 parent fbc6f2c commit b97ed1a
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Showing 2 changed files with 76 additions and 51 deletions.
122 changes: 73 additions & 49 deletions src/librustc_mir/interpret/cast.rs
View file
@@ -1,6 +1,5 @@
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;
Expand All @@ -12,25 +11,40 @@ use rustc_middle::ty::{self, Ty, TypeAndMut, TypeFoldable};
use rustc_span::symbol::sym;
use rustc_target::abi::{LayoutOf, Size, 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) => {
assert_eq!(
cast_ty, dest.layout.ty,
"mismatch of cast type {} and place type {}",
cast_ty, dest.layout.ty
);
self.unsize_into(src, 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 {
Expand Down Expand Up @@ -61,12 +75,12 @@ 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),
}
}

Expand Down Expand Up @@ -95,21 +109,21 @@ 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.
Expand All @@ -124,69 +138,79 @@ 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() && 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);
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
),
};
}
}

// # 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())
}

pub(super) 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>,
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 checks 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);
Scalar::from_uint(v, dest_layout.size)
let size = match cast_ty.kind {
// FIXME: Isn't there a helper for this? The same pattern occurs below.
Int(t) => {
t.bit_width().map(Size::from_bits).unwrap_or_else(|| self.pointer_size())
}
Uint(t) => {
t.bit_width().map(Size::from_bits).unwrap_or_else(|| self.pointer_size())
}
RawPtr(_) => self.pointer_size(),
_ => bug!(),
};
let v = truncate(v, size);
Scalar::from_uint(v, size)
}

Float(FloatTy::F32) if signed => Scalar::from_f32(Single::from_i128(v as i128).value),
Expand All @@ -200,7 +224,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}

// 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),
}
}

Expand Down Expand Up @@ -283,7 +307,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
src: OpTy<'tcx, M::PointerTag>,
dest: PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
trace!("Unsizing {:?} into {:?}", src, dest);
trace!("Unsizing {:?} of type {} into {:?}", *src, src.layout.ty, dest.layout.ty);
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, .. })) => {
Expand Down
5 changes: 3 additions & 2 deletions src/librustc_mir/interpret/step.rs
View file
Expand Up @@ -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) => {
Expand Down

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