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safe transmute: forbid reference lifetime extension

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Modifies `BikeshedIntrinsicFrom` to forbid lifetime extensions on
references. This static check can be opted out of with the
`Assume::lifetimes` flag.

Fixes #129097
This commit is contained in:
Jack Wrenn
2024-08-14 20:10:28 +00:00
parent 0f442e265c
commit 17995d5cc2
9 changed files with 535 additions and 132 deletions
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13
compiler/rustc_transmute/src/layout/mod.rs
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@@ -63,7 +63,9 @@ pub mod rustc {
use std::fmt::{self, Write};
use rustc_middle::mir::Mutability;
use rustc_middle::ty::{self, Ty};
use rustc_middle::ty::layout::{LayoutCx, LayoutError};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_target::abi::Layout;
/// A reference in the layout.
#[derive(Debug, Hash, Eq, PartialEq, Clone, Copy)]
@@ -120,4 +122,13 @@ pub mod rustc {
self != &Self::Primitive
}
}
pub(crate) fn layout_of<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
ty: Ty<'tcx>,
) -> Result<Layout<'tcx>, &'tcx LayoutError<'tcx>> {
use rustc_middle::ty::layout::LayoutOf;
let ty = cx.tcx.erase_regions(ty);
cx.layout_of(ty).map(|tl| tl.layout)
}
}

141
compiler/rustc_transmute/src/layout/tree.rs
View File

@@ -171,10 +171,12 @@ where
#[cfg(feature = "rustc")]
pub(crate) mod rustc {
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, LayoutError, LayoutOf};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, LayoutError};
use rustc_middle::ty::{self, AdtDef, AdtKind, List, ScalarInt, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::ErrorGuaranteed;
use rustc_target::abi::{FieldsShape, Size, TyAndLayout, Variants};
use rustc_target::abi::{
FieldIdx, FieldsShape, Layout, Size, TyAndLayout, VariantIdx, Variants,
};
use super::Tree;
use crate::layout::rustc::{Def, Ref};
@@ -202,20 +204,18 @@ pub(crate) mod rustc {
}
impl<'tcx> Tree<Def<'tcx>, Ref<'tcx>> {
pub fn from_ty(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
pub fn from_ty(ty: Ty<'tcx>, cx: LayoutCx<'tcx, TyCtxt<'tcx>>) -> Result<Self, Err> {
use rustc_target::abi::HasDataLayout;
let layout = ty_layout(cx, ty);
if let Err(e) = ty_and_layout.ty.error_reported() {
if let Err(e) = ty.error_reported() {
return Err(Err::TypeError(e));
}
let target = cx.tcx.data_layout();
let pointer_size = target.pointer_size;
match ty_and_layout.ty.kind() {
match ty.kind() {
ty::Bool => Ok(Self::bool()),
ty::Float(nty) => {
@@ -233,32 +233,30 @@ pub(crate) mod rustc {
Ok(Self::number(width as _))
}
ty::Tuple(members) => Self::from_tuple(ty_and_layout, members, cx),
ty::Tuple(members) => Self::from_tuple((ty, layout), members, cx),
ty::Array(inner_ty, len) => {
let FieldsShape::Array { stride, count } = &ty_and_layout.fields else {
let FieldsShape::Array { stride, count } = &layout.fields else {
return Err(Err::NotYetSupported);
};
let inner_ty_and_layout = cx.layout_of(*inner_ty)?;
assert_eq!(*stride, inner_ty_and_layout.size);
let elt = Tree::from_ty(inner_ty_and_layout, cx)?;
let inner_layout = ty_layout(cx, *inner_ty);
assert_eq!(*stride, inner_layout.size);
let elt = Tree::from_ty(*inner_ty, cx)?;
Ok(std::iter::repeat(elt)
.take(*count as usize)
.fold(Tree::unit(), |tree, elt| tree.then(elt)))
}
ty::Adt(adt_def, _args_ref) if !ty_and_layout.ty.is_box() => {
match adt_def.adt_kind() {
AdtKind::Struct => Self::from_struct(ty_and_layout, *adt_def, cx),
AdtKind::Enum => Self::from_enum(ty_and_layout, *adt_def, cx),
AdtKind::Union => Self::from_union(ty_and_layout, *adt_def, cx),
}
}
ty::Adt(adt_def, _args_ref) if !ty.is_box() => match adt_def.adt_kind() {
AdtKind::Struct => Self::from_struct((ty, layout), *adt_def, cx),
AdtKind::Enum => Self::from_enum((ty, layout), *adt_def, cx),
AdtKind::Union => Self::from_union((ty, layout), *adt_def, cx),
},
ty::Ref(lifetime, ty, mutability) => {
let ty_and_layout = cx.layout_of(*ty)?;
let align = ty_and_layout.align.abi.bytes_usize();
let size = ty_and_layout.size.bytes_usize();
let layout = ty_layout(cx, *ty);
let align = layout.align.abi.bytes_usize();
let size = layout.size.bytes_usize();
Ok(Tree::Ref(Ref {
lifetime: *lifetime,
ty: *ty,
@@ -274,21 +272,20 @@ pub(crate) mod rustc {
/// Constructs a `Tree` from a tuple.
fn from_tuple(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
members: &'tcx List<Ty<'tcx>>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
match &ty_and_layout.fields {
match &layout.fields {
FieldsShape::Primitive => {
assert_eq!(members.len(), 1);
let inner_ty = members[0];
let inner_ty_and_layout = cx.layout_of(inner_ty)?;
assert_eq!(ty_and_layout.layout, inner_ty_and_layout.layout);
Self::from_ty(inner_ty_and_layout, cx)
let inner_layout = ty_layout(cx, inner_ty);
Self::from_ty(inner_ty, cx)
}
FieldsShape::Arbitrary { offsets, .. } => {
assert_eq!(offsets.len(), members.len());
Self::from_variant(Def::Primitive, None, ty_and_layout, ty_and_layout.size, cx)
Self::from_variant(Def::Primitive, None, (ty, layout), layout.size, cx)
}
FieldsShape::Array { .. } | FieldsShape::Union(_) => Err(Err::NotYetSupported),
}
@@ -300,13 +297,13 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not a struct definition.
fn from_struct(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_struct());
let def = Def::Adt(def);
Self::from_variant(def, None, ty_and_layout, ty_and_layout.size, cx)
Self::from_variant(def, None, (ty, layout), layout.size, cx)
}
/// Constructs a `Tree` from an enum.
@@ -315,19 +312,18 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not an enum definition.
fn from_enum(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_enum());
let layout = ty_and_layout.layout;
// Computes the variant of a given index.
let layout_of_variant = |index| {
let tag = cx.tcx.tag_for_variant((ty_and_layout.ty, index));
let tag = cx.tcx.tag_for_variant((cx.tcx.erase_regions(ty), index));
let variant_def = Def::Variant(def.variant(index));
let variant_ty_and_layout = ty_and_layout.for_variant(&cx, index);
Self::from_variant(variant_def, tag, variant_ty_and_layout, layout.size, cx)
let variant_layout = ty_variant(cx, (ty, layout), index);
Self::from_variant(variant_def, tag, (ty, variant_layout), layout.size, cx)
};
// We consider three kinds of enums, each demanding a different
@@ -385,21 +381,20 @@ pub(crate) mod rustc {
fn from_variant(
def: Def<'tcx>,
tag: Option<ScalarInt>,
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
total_size: Size,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
// This constructor does not support non-`FieldsShape::Arbitrary`
// layouts.
let FieldsShape::Arbitrary { offsets, memory_index } = ty_and_layout.layout.fields()
else {
let FieldsShape::Arbitrary { offsets, memory_index } = layout.fields() else {
return Err(Err::NotYetSupported);
};
// When this function is invoked with enum variants,
// `ty_and_layout.size` does not encompass the entire size of the
// enum. We rely on `total_size` for this.
assert!(ty_and_layout.size <= total_size);
assert!(layout.size <= total_size);
let mut size = Size::ZERO;
let mut struct_tree = Self::def(def);
@@ -412,17 +407,18 @@ pub(crate) mod rustc {
// Append the fields, in memory order, to the layout.
let inverse_memory_index = memory_index.invert_bijective_mapping();
for (memory_idx, field_idx) in inverse_memory_index.iter_enumerated() {
for (memory_idx, &field_idx) in inverse_memory_index.iter_enumerated() {
// Add interfield padding.
let padding_needed = offsets[*field_idx] - size;
let padding_needed = offsets[field_idx] - size;
let padding = Self::padding(padding_needed.bytes_usize());
let field_ty_and_layout = ty_and_layout.field(&cx, field_idx.as_usize());
let field_tree = Self::from_ty(field_ty_and_layout, cx)?;
let field_ty = ty_field(cx, (ty, layout), field_idx);
let field_layout = ty_layout(cx, field_ty);
let field_tree = Self::from_ty(field_ty, cx)?;
struct_tree = struct_tree.then(padding).then(field_tree);
size += padding_needed + field_ty_and_layout.size;
size += padding_needed + field_layout.size;
}
// Add trailing padding.
@@ -457,28 +453,27 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not a union definition.
fn from_union(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_union());
let union_layout = ty_and_layout.layout;
// This constructor does not support non-`FieldsShape::Union`
// layouts. Fields of this shape are all placed at offset 0.
let FieldsShape::Union(fields) = union_layout.fields() else {
let FieldsShape::Union(fields) = layout.fields() else {
return Err(Err::NotYetSupported);
};
let fields = &def.non_enum_variant().fields;
let fields = fields.iter_enumerated().try_fold(
Self::uninhabited(),
|fields, (idx, ref field_def)| {
|fields, (idx, field_def)| {
let field_def = Def::Field(field_def);
let field_ty_and_layout = ty_and_layout.field(&cx, idx.as_usize());
let field = Self::from_ty(field_ty_and_layout, cx)?;
let trailing_padding_needed = union_layout.size - field_ty_and_layout.size;
let field_ty = ty_field(cx, (ty, layout), idx);
let field_layout = ty_layout(cx, field_ty);
let field = Self::from_ty(field_ty, cx)?;
let trailing_padding_needed = layout.size - field_layout.size;
let trailing_padding = Self::padding(trailing_padding_needed.bytes_usize());
let field_and_padding = field.then(trailing_padding);
Result::<Self, Err>::Ok(fields.or(field_and_padding))
@@ -488,4 +483,44 @@ pub(crate) mod rustc {
Ok(Self::def(Def::Adt(def)).then(fields))
}
}
pub(crate) fn ty_layout<'tcx>(cx: LayoutCx<'tcx, TyCtxt<'tcx>>, ty: Ty<'tcx>) -> Layout<'tcx> {
crate::layout::rustc::layout_of(cx, ty).unwrap()
}
fn ty_field<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: FieldIdx,
) -> Ty<'tcx> {
match ty.kind() {
ty::Adt(def, args) => {
match layout.variants {
Variants::Single { index } => {
let field = &def.variant(index).fields[i];
field.ty(cx.tcx, args)
}
// Discriminant field for enums (where applicable).
Variants::Multiple { tag, .. } => {
assert_eq!(i.as_usize(), 0);
ty::layout::PrimitiveExt::to_ty(&tag.primitive(), cx.tcx)
}
}
}
ty::Tuple(fields) => fields[i.as_usize()],
kind @ _ => unimplemented!(
"only a subset of `Ty::ty_and_layout_field`'s functionality is implemented. implementation needed for {:?}",
kind
),
}
}
fn ty_variant<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: VariantIdx,
) -> Layout<'tcx> {
let ty = cx.tcx.erase_regions(ty);
TyAndLayout { ty, layout }.for_variant(&cx, i).layout
}
}

2
compiler/rustc_transmute/src/lib.rs
View File

@@ -9,7 +9,7 @@ pub(crate) use rustc_data_structures::fx::{FxIndexMap as Map, FxIndexSet as Set}
pub mod layout;
mod maybe_transmutable;
#[derive(Default)]
#[derive(Copy, Clone, Debug, Default)]
pub struct Assume {
pub alignment: bool,
pub lifetimes: bool,

7
compiler/rustc_transmute/src/maybe_transmutable/mod.rs
View File

@@ -30,7 +30,7 @@ where
// FIXME: Nix this cfg, so we can write unit tests independently of rustc
#[cfg(feature = "rustc")]
mod rustc {
use rustc_middle::ty::layout::{LayoutCx, LayoutOf};
use rustc_middle::ty::layout::LayoutCx;
use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
use super::*;
@@ -45,10 +45,9 @@ mod rustc {
let layout_cx = LayoutCx { tcx: context, param_env: ParamEnv::reveal_all() };
let layout_of = |ty| {
layout_cx
.layout_of(ty)
crate::layout::rustc::layout_of(layout_cx, ty)
.map_err(|_| Err::NotYetSupported)
.and_then(|tl| Tree::from_ty(tl, layout_cx))
.and_then(|_| Tree::from_ty(ty, layout_cx))
};
// Convert `src` and `dst` from their rustc representations, to `Tree`-based