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tighten CTFE safety net for accesses to globals

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This commit is contained in:
Ralf Jung 2020-04-09 11:32:43 +02:00
parent 11f6096a9e
commit d69c668111
1 changed files with 23 additions and 8 deletions
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31
src/librustc_mir/const_eval/machine.rs
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@ -350,15 +350,30 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter {
static_def_id: Option<DefId>,
is_write: bool,
) -> InterpResult<'tcx> {
if is_write && allocation.mutability == Mutability::Not {
Err(err_ub!(WriteToReadOnly(alloc_id)).into())
} else if is_write {
Err(ConstEvalErrKind::ModifiedGlobal.into())
} else if memory_extra.can_access_statics || static_def_id.is_none() {
// `static_def_id.is_none()` indicates this is not a static, but a const or so.
Ok(())
if is_write {
// Write access. These are never allowed, but we give a targeted error message.
if allocation.mutability == Mutability::Not {
Err(err_ub!(WriteToReadOnly(alloc_id)).into())
} else {
Err(ConstEvalErrKind::ModifiedGlobal.into())
}
} else {
Err(ConstEvalErrKind::ConstAccessesStatic.into())
// Read access. These are usually allowed, with some exceptions.
if memory_extra.can_access_statics {
// This is allowed to read from anything.
Ok(())
} else if allocation.mutability == Mutability::Mut || static_def_id.is_some() {
// This is a potentially dangerous read.
// We *must* error on any access to a mutable global here, as the content of
// this allocation may be different now and at run-time, so if we permit reading
// now we might return the wrong value.
// We conservatively also reject all statics here, but that could be relaxed
// in the future.
Err(ConstEvalErrKind::ConstAccessesStatic.into())
} else {
// Immutable global, this read is fine.
Ok(())
}
}
}
}