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Miri: add a flag to do recursive validity checking

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This commit is contained in:
Ralf Jung
2024-08-02 10:29:52 +02:00
parent 2cec7a85ed
commit 21c02517c3
14 changed files with 186 additions and 107 deletions
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176
compiler/rustc_const_eval/src/interpret/validity.rs
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@@ -155,8 +155,8 @@ impl CtfeValidationMode {
/// State for tracking recursive validation of references
pub struct RefTracking<T, PATH = ()> {
pub seen: FxHashSet<T>,
pub todo: Vec<(T, PATH)>,
seen: FxHashSet<T>,
todo: Vec<(T, PATH)>,
}
impl<T: Clone + Eq + Hash + std::fmt::Debug, PATH: Default> RefTracking<T, PATH> {
@@ -169,8 +169,11 @@ impl<T: Clone + Eq + Hash + std::fmt::Debug, PATH: Default> RefTracking<T, PATH>
ref_tracking_for_consts.seen.insert(op);
ref_tracking_for_consts
}
pub fn next(&mut self) -> Option<(T, PATH)> {
self.todo.pop()
}
pub fn track(&mut self, op: T, path: impl FnOnce() -> PATH) {
fn track(&mut self, op: T, path: impl FnOnce() -> PATH) {
if self.seen.insert(op.clone()) {
trace!("Recursing below ptr {:#?}", op);
let path = path();
@@ -435,88 +438,96 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
if self.ecx.scalar_may_be_null(Scalar::from_maybe_pointer(place.ptr(), self.ecx))? {
throw_validation_failure!(self.path, NullPtr { ptr_kind })
}
// Do not allow pointers to uninhabited types.
// Do not allow references to uninhabited types.
if place.layout.abi.is_uninhabited() {
let ty = place.layout.ty;
throw_validation_failure!(self.path, PtrToUninhabited { ptr_kind, ty })
}
// Recursive checking
if let Some(ref_tracking) = self.ref_tracking.as_deref_mut() {
// Determine whether this pointer expects to be pointing to something mutable.
let ptr_expected_mutbl = match ptr_kind {
PointerKind::Box => Mutability::Mut,
PointerKind::Ref(mutbl) => {
// We do not take into account interior mutability here since we cannot know if
// there really is an `UnsafeCell` inside `Option<UnsafeCell>` -- so we check
// that in the recursive descent behind this reference (controlled by
// `allow_immutable_unsafe_cell`).
mutbl
}
};
// Proceed recursively even for ZST, no reason to skip them!
// `!` is a ZST and we want to validate it.
if let Ok((alloc_id, _offset, _prov)) = self.ecx.ptr_try_get_alloc_id(place.ptr(), 0) {
if let Some(ctfe_mode) = self.ctfe_mode {
let mut skip_recursive_check = false;
if let Some(GlobalAlloc::Static(did)) = self.ecx.tcx.try_get_global_alloc(alloc_id)
// CTFE imposes restrictions on what references can point to.
if let Ok((alloc_id, _offset, _prov)) =
self.ecx.ptr_try_get_alloc_id(place.ptr(), 0)
{
let DefKind::Static { nested, .. } = self.ecx.tcx.def_kind(did) else { bug!() };
// Special handling for pointers to statics (irrespective of their type).
assert!(!self.ecx.tcx.is_thread_local_static(did));
assert!(self.ecx.tcx.is_static(did));
// Mode-specific checks
match self.ctfe_mode {
Some(
CtfeValidationMode::Static { .. } | CtfeValidationMode::Promoted { .. },
) => {
// We skip recursively checking other statics. These statics must be sound by
// themselves, and the only way to get broken statics here is by using
// unsafe code.
// The reasons we don't check other statics is twofold. For one, in all
// sound cases, the static was already validated on its own, and second, we
// trigger cycle errors if we try to compute the value of the other static
// and that static refers back to us (potentially through a promoted).
// This could miss some UB, but that's fine.
// We still walk nested allocations, as they are fundamentally part of this validation run.
// This means we will also recurse into nested statics of *other*
// statics, even though we do not recurse into other statics directly.
// That's somewhat inconsistent but harmless.
skip_recursive_check = !nested;
}
Some(CtfeValidationMode::Const { .. }) => {
// We can't recursively validate `extern static`, so we better reject them.
if self.ecx.tcx.is_foreign_item(did) {
throw_validation_failure!(self.path, ConstRefToExtern);
if let Some(GlobalAlloc::Static(did)) =
self.ecx.tcx.try_get_global_alloc(alloc_id)
{
let DefKind::Static { nested, .. } = self.ecx.tcx.def_kind(did) else {
bug!()
};
// Special handling for pointers to statics (irrespective of their type).
assert!(!self.ecx.tcx.is_thread_local_static(did));
assert!(self.ecx.tcx.is_static(did));
// Mode-specific checks
match ctfe_mode {
CtfeValidationMode::Static { .. }
| CtfeValidationMode::Promoted { .. } => {
// We skip recursively checking other statics. These statics must be sound by
// themselves, and the only way to get broken statics here is by using
// unsafe code.
// The reasons we don't check other statics is twofold. For one, in all
// sound cases, the static was already validated on its own, and second, we
// trigger cycle errors if we try to compute the value of the other static
// and that static refers back to us (potentially through a promoted).
// This could miss some UB, but that's fine.
// We still walk nested allocations, as they are fundamentally part of this validation run.
// This means we will also recurse into nested statics of *other*
// statics, even though we do not recurse into other statics directly.
// That's somewhat inconsistent but harmless.
skip_recursive_check = !nested;
}
CtfeValidationMode::Const { .. } => {
// We can't recursively validate `extern static`, so we better reject them.
if self.ecx.tcx.is_foreign_item(did) {
throw_validation_failure!(self.path, ConstRefToExtern);
}
}
}
None => {}
}
}
// Dangling and Mutability check.
let (size, _align, alloc_kind) = self.ecx.get_alloc_info(alloc_id);
if alloc_kind == AllocKind::Dead {
// This can happen for zero-sized references. We can't have *any* references to non-existing
// allocations though, interning rejects them all as the rest of rustc isn't happy with them...
// so we throw an error, even though this isn't really UB.
// A potential future alternative would be to resurrect this as a zero-sized allocation
// (which codegen will then compile to an aligned dummy pointer anyway).
throw_validation_failure!(self.path, DanglingPtrUseAfterFree { ptr_kind });
}
// If this allocation has size zero, there is no actual mutability here.
if size != Size::ZERO {
let alloc_actual_mutbl = mutability(self.ecx, alloc_id);
// Mutable pointer to immutable memory is no good.
if ptr_expected_mutbl == Mutability::Mut
&& alloc_actual_mutbl == Mutability::Not
{
throw_validation_failure!(self.path, MutableRefToImmutable);
// Dangling and Mutability check.
let (size, _align, alloc_kind) = self.ecx.get_alloc_info(alloc_id);
if alloc_kind == AllocKind::Dead {
// This can happen for zero-sized references. We can't have *any* references to
// non-existing allocations in const-eval though, interning rejects them all as
// the rest of rustc isn't happy with them... so we throw an error, even though
// this isn't really UB.
// A potential future alternative would be to resurrect this as a zero-sized allocation
// (which codegen will then compile to an aligned dummy pointer anyway).
throw_validation_failure!(self.path, DanglingPtrUseAfterFree { ptr_kind });
}
// In a const, everything must be completely immutable.
if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. })) {
// If this allocation has size zero, there is no actual mutability here.
if size != Size::ZERO {
// Determine whether this pointer expects to be pointing to something mutable.
let ptr_expected_mutbl = match ptr_kind {
PointerKind::Box => Mutability::Mut,
PointerKind::Ref(mutbl) => {
// We do not take into account interior mutability here since we cannot know if
// there really is an `UnsafeCell` inside `Option<UnsafeCell>` -- so we check
// that in the recursive descent behind this reference (controlled by
// `allow_immutable_unsafe_cell`).
mutbl
}
};
// Determine what it actually points to.
let alloc_actual_mutbl = mutability(self.ecx, alloc_id);
// Mutable pointer to immutable memory is no good.
if ptr_expected_mutbl == Mutability::Mut
|| alloc_actual_mutbl == Mutability::Mut
&& alloc_actual_mutbl == Mutability::Not
{
throw_validation_failure!(self.path, ConstRefToMutable);
throw_validation_failure!(self.path, MutableRefToImmutable);
}
// In a const, everything must be completely immutable.
if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. })) {
if ptr_expected_mutbl == Mutability::Mut
|| alloc_actual_mutbl == Mutability::Mut
{
throw_validation_failure!(self.path, ConstRefToMutable);
}
}
}
}
@@ -524,6 +535,15 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
if skip_recursive_check {
return Ok(());
}
} else {
// This is not CTFE, so it's Miri with recursive checking.
// FIXME: we do *not* check behind boxes, since creating a new box first creates it uninitialized
// and then puts the value in there, so briefly we have a box with uninit contents.
// FIXME: should we also skip `UnsafeCell` behind shared references? Currently that is not
// needed since validation reads bypass Stacked Borrows and data race checks.
if matches!(ptr_kind, PointerKind::Box) {
return Ok(());
}
}
let path = &self.path;
ref_tracking.track(place, || {
@@ -1072,11 +1092,23 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
/// `op` is assumed to cover valid memory if it is an indirect operand.
/// It will error if the bits at the destination do not match the ones described by the layout.
#[inline(always)]
pub fn validate_operand(&self, op: &OpTy<'tcx, M::Provenance>) -> InterpResult<'tcx> {
pub fn validate_operand(
&self,
op: &OpTy<'tcx, M::Provenance>,
recursive: bool,
) -> InterpResult<'tcx> {
// Note that we *could* actually be in CTFE here with `-Zextra-const-ub-checks`, but it's
// still correct to not use `ctfe_mode`: that mode is for validation of the final constant
// value, it rules out things like `UnsafeCell` in awkward places. It also can make checking
// recurse through references which, for now, we don't want here, either.
self.validate_operand_internal(op, vec![], None, None)
// value, it rules out things like `UnsafeCell` in awkward places.
if !recursive {
return self.validate_operand_internal(op, vec![], None, None);
}
// Do a recursive check.
let mut ref_tracking = RefTracking::empty();
self.validate_operand_internal(op, vec![], Some(&mut ref_tracking), None)?;
while let Some((mplace, path)) = ref_tracking.todo.pop() {
self.validate_operand_internal(&mplace.into(), path, Some(&mut ref_tracking), None)?;
}
Ok(())
}
}