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Fix MIR typeck soundness holes #69145

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Feb 20, 2020
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70 changes: 41 additions & 29 deletions src/librustc_mir/borrow_check/type_check/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -309,6 +309,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
);
}
} else {
let tcx = self.tcx();
if let ty::ConstKind::Unevaluated(def_id, substs, promoted) = constant.literal.val {
if let Some(promoted) = promoted {
let check_err = |verifier: &mut TypeVerifier<'a, 'b, 'tcx>,
Expand Down Expand Up @@ -358,10 +359,23 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
);
}
}
} else if let Some(static_def_id) = constant.check_static_ptr(tcx) {
let unnormalized_ty = tcx.type_of(static_def_id);
let locations = location.to_locations();
let normalized_ty = self.cx.normalize(unnormalized_ty, locations);
let literal_ty = constant.literal.ty.builtin_deref(true).unwrap().ty;

if let Err(terr) = self.cx.eq_types(
normalized_ty,
literal_ty,
locations,
ConstraintCategory::Boring,
) {
span_mirbug!(self, constant, "bad static type {:?} ({:?})", constant, terr);
}
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This is another thing where I don't understand why the new static representation doesn't result in correctness by default.

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Could MIR building inject a UserTypeAnnotation for static references/pointers? (note that I don't want to block this PR, any fix here should be equivalent, so we can clean it up later)

}
if let ty::FnDef(def_id, substs) = constant.literal.ty.kind {
let tcx = self.tcx();

if let ty::FnDef(def_id, substs) = constant.literal.ty.kind {
let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
self.cx.normalize_and_prove_instantiated_predicates(
instantiated_predicates,
Expand Down Expand Up @@ -466,33 +480,6 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {

let mut place_ty = PlaceTy::from_ty(self.body.local_decls[place.local].ty);

if place.projection.is_empty() {
if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
let tcx = self.tcx();
let trait_ref = ty::TraitRef {
def_id: tcx.lang_items().copy_trait().unwrap(),
substs: tcx.mk_substs_trait(place_ty.ty, &[]),
};

// To have a `Copy` operand, the type `T` of the
// value must be `Copy`. Note that we prove that `T: Copy`,
// rather than using the `is_copy_modulo_regions`
// test. This is important because
// `is_copy_modulo_regions` ignores the resulting region
// obligations and assumes they pass. This can result in
// bounds from `Copy` impls being unsoundly ignored (e.g.,
// #29149). Note that we decide to use `Copy` before knowing
// whether the bounds fully apply: in effect, the rule is
// that if a value of some type could implement `Copy`, then
// it must.
self.cx.prove_trait_ref(
trait_ref,
location.to_locations(),
ConstraintCategory::CopyBound,
);
}
}

for elem in place.projection.iter() {
if place_ty.variant_index.is_none() {
if place_ty.ty.references_error() {
Expand All @@ -503,6 +490,31 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
place_ty = self.sanitize_projection(place_ty, elem, place, location)
}

if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
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The main change here is that we now do this for all places, right? I wonder why we didn't before? That just seems like a silly oversight to me.

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yes

let tcx = self.tcx();
let trait_ref = ty::TraitRef {
def_id: tcx.lang_items().copy_trait().unwrap(),
substs: tcx.mk_substs_trait(place_ty.ty, &[]),
};

// To have a `Copy` operand, the type `T` of the
// value must be `Copy`. Note that we prove that `T: Copy`,
// rather than using the `is_copy_modulo_regions`
// test. This is important because
// `is_copy_modulo_regions` ignores the resulting region
// obligations and assumes they pass. This can result in
// bounds from `Copy` impls being unsoundly ignored (e.g.,
// #29149). Note that we decide to use `Copy` before knowing
// whether the bounds fully apply: in effect, the rule is
// that if a value of some type could implement `Copy`, then
// it must.
self.cx.prove_trait_ref(
trait_ref,
location.to_locations(),
ConstraintCategory::CopyBound,
);
}

place_ty
}

Expand Down
12 changes: 12 additions & 0 deletions src/test/ui/nll/do-not-ignore-lifetime-bounds-in-copy-proj.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
// Test that the 'static bound from the Copy impl is respected. Regression test for #29149.

#[derive(Clone)]
struct Foo<'a>(&'a u32);
impl Copy for Foo<'static> {}

fn main() {
let s = 2;
let a = (Foo(&s),); //~ ERROR `s` does not live long enough [E0597]
drop(a.0);
drop(a.0);
}
14 changes: 14 additions & 0 deletions src/test/ui/nll/do-not-ignore-lifetime-bounds-in-copy-proj.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
error[E0597]: `s` does not live long enough
--> $DIR/do-not-ignore-lifetime-bounds-in-copy-proj.rs:9:18
|
LL | let a = (Foo(&s),);
| ^^ borrowed value does not live long enough
LL | drop(a.0);
| --- copying this value requires that `s` is borrowed for `'static`
LL | drop(a.0);
LL | }
| - `s` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.
30 changes: 30 additions & 0 deletions src/test/ui/nll/issue-69114-static-mut-ty.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
// Check that borrowck ensures that `static mut` items have the expected type.

static FOO: u8 = 42;
static mut BAR: &'static u8 = &FOO;
static mut BAR_ELIDED: &u8 = &FOO;

fn main() {
unsafe {
println!("{} {}", BAR, BAR_ELIDED);
set_bar();
set_bar_elided();
println!("{} {}", BAR, BAR_ELIDED);
}
}

fn set_bar() {
let n = 42;
unsafe {
BAR = &n;
//~^ ERROR does not live long enough
}
}

fn set_bar_elided() {
let n = 42;
unsafe {
BAR_ELIDED = &n;
//~^ ERROR does not live long enough
}
}
27 changes: 27 additions & 0 deletions src/test/ui/nll/issue-69114-static-mut-ty.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
error[E0597]: `n` does not live long enough
--> $DIR/issue-69114-static-mut-ty.rs:19:15
|
LL | BAR = &n;
| ------^^
| | |
| | borrowed value does not live long enough
| assignment requires that `n` is borrowed for `'static`
...
LL | }
| - `n` dropped here while still borrowed

error[E0597]: `n` does not live long enough
--> $DIR/issue-69114-static-mut-ty.rs:27:22
|
LL | BAR_ELIDED = &n;
| -------------^^
| | |
| | borrowed value does not live long enough
| assignment requires that `n` is borrowed for `'static`
...
LL | }
| - `n` dropped here while still borrowed

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0597`.
9 changes: 9 additions & 0 deletions src/test/ui/nll/issue-69114-static-ty.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
// Check that borrowck ensures that `static` items have the expected type.

static FOO: &'static (dyn Fn(&'static u8) + Send + Sync) = &drop;

fn main() {
let n = 42;
FOO(&n);
//~^ ERROR does not live long enough
}
15 changes: 15 additions & 0 deletions src/test/ui/nll/issue-69114-static-ty.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
error[E0597]: `n` does not live long enough
--> $DIR/issue-69114-static-ty.rs:7:9
|
LL | FOO(&n);
| ----^^-
| | |
| | borrowed value does not live long enough
| argument requires that `n` is borrowed for `'static`
LL |
LL | }
| - `n` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.