Auto merge of rust-lang#54461 - RalfJung:pointer-provenance, r=oli-obk

miri engine: basic support for pointer provenance tracking

This enriches pointers with a new member, `tag`, that can be used to do provenance tracking. This is a new type parameter that propagates up through everything. It defaults to `()` (no tag), which is also the value used by CTFE -- but miri will use another type.

The only actually interesting piece here, I think, is what I had to do in the memory's `get`. The problem is that `tcx` (storing the allocations for statics) uses `()` for provenance information. But the machine might need another tag. The machine has a function to do the conversion, but if a conversion actually happened, we need to store the result of this *somewhere* -- we cannot return a pointer into `tcx` as we usually would.
So I introduced `MonoHashMap` which uses `RefCell` to be able to insert new entries even when we just have a shared ref. However, it is important that we can also return shared refs into the map without holding the `RefCell` opan. This is achieved by boxing the values stored in the map, so their addresses remain stable even when the map's table gets reallocated. This is all implemented in `mono_hash_map.rs`.

NOTE: This PR also contains the commits from rust-lang#54380 (comment). Only the [last two commits](https://github.com/rust-lang/rust/pull/54461/files/8e74ee0998a5b11f28d61600dbb881c7168a4a40..HEAD) are new.

Author: bors

src/librustc/ich/impls_ty.rs

@@ -391,10 +391,39 @@ for ::mir::interpret::ConstValue<'gcx> {
     }
 }
 
-impl_stable_hash_for!(struct mir::interpret::Pointer {
-    alloc_id,
-    offset
-});
+impl<'a, Tag> HashStable<StableHashingContext<'a>>
+for ::mir::interpret::Pointer<Tag>
+where Tag: HashStable<StableHashingContext<'a>>
+{
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'a>,
+                                          hasher: &mut StableHasher<W>) {
+        let ::mir::interpret::Pointer { alloc_id, offset, tag } = self;
+        alloc_id.hash_stable(hcx, hasher);
+        offset.hash_stable(hcx, hasher);
+        tag.hash_stable(hcx, hasher);
+    }
+}
+
+impl<'a, Tag> HashStable<StableHashingContext<'a>>
+for ::mir::interpret::Scalar<Tag>
+where Tag: HashStable<StableHashingContext<'a>>
+{
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'a>,
+                                          hasher: &mut StableHasher<W>) {
+        use mir::interpret::Scalar::*;
+
+        mem::discriminant(self).hash_stable(hcx, hasher);
+        match self {
+            Bits { bits, size } => {
+                bits.hash_stable(hcx, hasher);
+                size.hash_stable(hcx, hasher);
+            },
+            Ptr(ptr) => ptr.hash_stable(hcx, hasher),
+        }
+    }
+}
 
 impl<'a> HashStable<StableHashingContext<'a>> for mir::interpret::AllocId {
     fn hash_stable<W: StableHasherResult>(
@@ -449,25 +478,6 @@ impl_stable_hash_for!(enum ::syntax::ast::Mutability {
     Mutable
 });
 
-
-impl<'a> HashStable<StableHashingContext<'a>>
-for ::mir::interpret::Scalar {
-    fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'a>,
-                                          hasher: &mut StableHasher<W>) {
-        use mir::interpret::Scalar::*;
-
-        mem::discriminant(self).hash_stable(hcx, hasher);
-        match *self {
-            Bits { bits, size } => {
-                bits.hash_stable(hcx, hasher);
-                size.hash_stable(hcx, hasher);
-            },
-            Ptr(ptr) => ptr.hash_stable(hcx, hasher),
-        }
-    }
-}
-
 impl_stable_hash_for!(struct ty::Const<'tcx> {
     ty,
     val

src/librustc/mir/interpret/mod.rs

@@ -138,54 +138,82 @@ impl<T: layout::HasDataLayout> PointerArithmetic for T {}
 /// each context.
 ///
 /// Defaults to the index based and loosely coupled AllocId.
+///
+/// Pointer is also generic over the `Tag` associated with each pointer,
+/// which is used to do provenance tracking during execution.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
-pub struct Pointer<Id=AllocId> {
+pub struct Pointer<Tag=(),Id=AllocId> {
     pub alloc_id: Id,
     pub offset: Size,
+    pub tag: Tag,
 }
 
 /// Produces a `Pointer` which points to the beginning of the Allocation
 impl From<AllocId> for Pointer {
+    #[inline(always)]
     fn from(alloc_id: AllocId) -> Self {
         Pointer::new(alloc_id, Size::ZERO)
     }
 }
 
-impl<'tcx> Pointer {
+impl<'tcx> Pointer<()> {
+    #[inline(always)]
     pub fn new(alloc_id: AllocId, offset: Size) -> Self {
-        Pointer { alloc_id, offset }
+        Pointer { alloc_id, offset, tag: () }
+    }
+
+    #[inline(always)]
+    pub fn with_default_tag<Tag>(self) -> Pointer<Tag>
+        where Tag: Default
+    {
+        Pointer::new_with_tag(self.alloc_id, self.offset, Default::default())
+    }
+}
+
+impl<'tcx, Tag> Pointer<Tag> {
+    #[inline(always)]
+    pub fn new_with_tag(alloc_id: AllocId, offset: Size, tag: Tag) -> Self {
+        Pointer { alloc_id, offset, tag }
     }
 
     pub fn wrapping_signed_offset<C: HasDataLayout>(self, i: i64, cx: C) -> Self {
-        Pointer::new(
+        Pointer::new_with_tag(
             self.alloc_id,
             Size::from_bytes(cx.data_layout().wrapping_signed_offset(self.offset.bytes(), i)),
+            self.tag,
         )
     }
 
     pub fn overflowing_signed_offset<C: HasDataLayout>(self, i: i128, cx: C) -> (Self, bool) {
         let (res, over) = cx.data_layout().overflowing_signed_offset(self.offset.bytes(), i);
-        (Pointer::new(self.alloc_id, Size::from_bytes(res)), over)
+        (Pointer::new_with_tag(self.alloc_id, Size::from_bytes(res), self.tag), over)
     }
 
     pub fn signed_offset<C: HasDataLayout>(self, i: i64, cx: C) -> EvalResult<'tcx, Self> {
-        Ok(Pointer::new(
+        Ok(Pointer::new_with_tag(
             self.alloc_id,
             Size::from_bytes(cx.data_layout().signed_offset(self.offset.bytes(), i)?),
+            self.tag,
         ))
     }
 
     pub fn overflowing_offset<C: HasDataLayout>(self, i: Size, cx: C) -> (Self, bool) {
         let (res, over) = cx.data_layout().overflowing_offset(self.offset.bytes(), i.bytes());
-        (Pointer::new(self.alloc_id, Size::from_bytes(res)), over)
+        (Pointer::new_with_tag(self.alloc_id, Size::from_bytes(res), self.tag), over)
     }
 
     pub fn offset<C: HasDataLayout>(self, i: Size, cx: C) -> EvalResult<'tcx, Self> {
-        Ok(Pointer::new(
+        Ok(Pointer::new_with_tag(
             self.alloc_id,
             Size::from_bytes(cx.data_layout().offset(self.offset.bytes(), i.bytes())?),
+            self.tag
         ))
     }
+
+    #[inline]
+    pub fn erase_tag(self) -> Pointer {
+        Pointer { alloc_id: self.alloc_id, offset: self.offset, tag: () }
+    }
 }
 
 
@@ -496,15 +524,15 @@ impl<'tcx, M: fmt::Debug + Eq + Hash + Clone> AllocMap<'tcx, M> {
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
-pub struct Allocation {
+pub struct Allocation<Tag=()> {
     /// The actual bytes of the allocation.
     /// Note that the bytes of a pointer represent the offset of the pointer
     pub bytes: Vec<u8>,
-    /// Maps from byte addresses to allocations.
+    /// Maps from byte addresses to extra data for each pointer.
     /// Only the first byte of a pointer is inserted into the map; i.e.,
     /// every entry in this map applies to `pointer_size` consecutive bytes starting
     /// at the given offset.
-    pub relocations: Relocations,
+    pub relocations: Relocations<Tag>,
     /// Denotes undefined memory. Reading from undefined memory is forbidden in miri
     pub undef_mask: UndefMask,
     /// The alignment of the allocation to detect unaligned reads.
@@ -515,7 +543,7 @@ pub struct Allocation {
     pub mutability: Mutability,
 }
 
-impl Allocation {
+impl<Tag> Allocation<Tag> {
     /// Creates a read-only allocation initialized by the given bytes
     pub fn from_bytes(slice: &[u8], align: Align) -> Self {
         let mut undef_mask = UndefMask::new(Size::ZERO);
@@ -548,29 +576,29 @@ impl Allocation {
 impl<'tcx> ::serialize::UseSpecializedDecodable for &'tcx Allocation {}
 
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
-pub struct Relocations<Id=AllocId>(SortedMap<Size, Id>);
+pub struct Relocations<Tag=(), Id=AllocId>(SortedMap<Size, (Tag, Id)>);
 
-impl<Id> Relocations<Id> {
+impl<Tag, Id> Relocations<Tag, Id> {
     pub fn new() -> Self {
         Relocations(SortedMap::new())
     }
 
     // The caller must guarantee that the given relocations are already sorted
     // by address and contain no duplicates.
-    pub fn from_presorted(r: Vec<(Size, Id)>) -> Self {
+    pub fn from_presorted(r: Vec<(Size, (Tag, Id))>) -> Self {
         Relocations(SortedMap::from_presorted_elements(r))
     }
 }
 
-impl Deref for Relocations {
-    type Target = SortedMap<Size, AllocId>;
+impl<Tag> Deref for Relocations<Tag> {
+    type Target = SortedMap<Size, (Tag, AllocId)>;
 
     fn deref(&self) -> &Self::Target {
         &self.0
     }
 }
 
-impl DerefMut for Relocations {
+impl<Tag> DerefMut for Relocations<Tag> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }

src/librustc/mir/interpret/value.rs

@@ -79,7 +79,47 @@ impl<'tcx> ConstValue<'tcx> {
     }
 }
 
-impl<'tcx> Scalar {
+/// A `Scalar` represents an immediate, primitive value existing outside of a
+/// `memory::Allocation`. It is in many ways like a small chunk of a `Allocation`, up to 8 bytes in
+/// size. Like a range of bytes in an `Allocation`, a `Scalar` can either represent the raw bytes
+/// of a simple value or a pointer into another `Allocation`
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
+pub enum Scalar<Tag=(), Id=AllocId> {
+    /// The raw bytes of a simple value.
+    Bits {
+        /// The first `size` bytes are the value.
+        /// Do not try to read less or more bytes that that. The remaining bytes must be 0.
+        size: u8,
+        bits: u128,
+    },
+
+    /// A pointer into an `Allocation`. An `Allocation` in the `memory` module has a list of
+    /// relocations, but a `Scalar` is only large enough to contain one, so we just represent the
+    /// relocation and its associated offset together as a `Pointer` here.
+    Ptr(Pointer<Tag, Id>),
+}
+
+impl<'tcx> Scalar<()> {
+    #[inline]
+    pub fn with_default_tag<Tag>(self) -> Scalar<Tag>
+        where Tag: Default
+    {
+        match self {
+            Scalar::Ptr(ptr) => Scalar::Ptr(ptr.with_default_tag()),
+            Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
+        }
+    }
+}
+
+impl<'tcx, Tag> Scalar<Tag> {
+    #[inline]
+    pub fn erase_tag(self) -> Scalar {
+        match self {
+            Scalar::Ptr(ptr) => Scalar::Ptr(ptr.erase_tag()),
+            Scalar::Bits { bits, size } => Scalar::Bits { bits, size },
+        }
+    }
+
     #[inline]
     pub fn ptr_null(cx: impl HasDataLayout) -> Self {
         Scalar::Bits {
@@ -208,7 +248,7 @@ impl<'tcx> Scalar {
     }
 
     #[inline]
-    pub fn to_ptr(self) -> EvalResult<'tcx, Pointer> {
+    pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
         match self {
             Scalar::Bits { bits: 0, .. } => err!(InvalidNullPointerUsage),
             Scalar::Bits { .. } => err!(ReadBytesAsPointer),
@@ -317,29 +357,9 @@ impl<'tcx> Scalar {
     }
 }
 
-impl From<Pointer> for Scalar {
+impl<Tag> From<Pointer<Tag>> for Scalar<Tag> {
     #[inline(always)]
-    fn from(ptr: Pointer) -> Self {
+    fn from(ptr: Pointer<Tag>) -> Self {
         Scalar::Ptr(ptr)
     }
 }
-
-/// A `Scalar` represents an immediate, primitive value existing outside of a
-/// `memory::Allocation`. It is in many ways like a small chunk of a `Allocation`, up to 8 bytes in
-/// size. Like a range of bytes in an `Allocation`, a `Scalar` can either represent the raw bytes
-/// of a simple value or a pointer into another `Allocation`
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
-pub enum Scalar<Id=AllocId> {
-    /// The raw bytes of a simple value.
-    Bits {
-        /// The first `size` bytes are the value.
-        /// Do not try to read less or more bytes that that. The remaining bytes must be 0.
-        size: u8,
-        bits: u128,
-    },
-
-    /// A pointer into an `Allocation`. An `Allocation` in the `memory` module has a list of
-    /// relocations, but a `Scalar` is only large enough to contain one, so we just represent the
-    /// relocation and its associated offset together as a `Pointer` here.
-    Ptr(Pointer<Id>),
-}

src/librustc_codegen_llvm/mir/constant.rs

@@ -92,7 +92,7 @@ pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll
     let pointer_size = layout.pointer_size.bytes() as usize;
 
     let mut next_offset = 0;
-    for &(offset, alloc_id) in alloc.relocations.iter() {
+    for &(offset, ((), alloc_id)) in alloc.relocations.iter() {
         let offset = offset.bytes();
         assert_eq!(offset as usize as u64, offset);
         let offset = offset as usize;
@@ -105,7 +105,7 @@ pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll
         ).expect("const_alloc_to_llvm: could not read relocation pointer") as u64;
         llvals.push(scalar_to_llvm(
             cx,
-            Pointer { alloc_id, offset: Size::from_bytes(ptr_offset) }.into(),
+            Pointer::new(alloc_id, Size::from_bytes(ptr_offset)).into(),
             &layout::Scalar {
                 value: layout::Primitive::Pointer,
                 valid_range: 0..=!0