Initial work on permissive provenance

src/bin/miri.rs

@@ -30,7 +30,7 @@ use rustc_middle::{
 };
 use rustc_session::{config::ErrorOutputType, search_paths::PathKind, CtfeBacktrace};
 
-use miri::BacktraceStyle;
+use miri::{BacktraceStyle, ProvenanceMode};
 
 struct MiriCompilerCalls {
     miri_config: miri::MiriConfig,
@@ -384,10 +384,14 @@ fn main() {
                     miri_config.tag_raw = true;
                 }
                 "-Zmiri-strict-provenance" => {
-                    miri_config.strict_provenance = true;
+                    miri_config.provenance_mode = ProvenanceMode::Strict;
                     miri_config.tag_raw = true;
                     miri_config.check_number_validity = true;
                 }
+                "-Zmiri-permissive-provenance" => {
+                    miri_config.provenance_mode = ProvenanceMode::Permissive;
+                    miri_config.tag_raw = true;
+                }
                 "-Zmiri-mute-stdout-stderr" => {
                     miri_config.mute_stdout_stderr = true;
                 }

src/eval.rs

@@ -113,9 +113,8 @@ pub struct MiriConfig {
     pub panic_on_unsupported: bool,
     /// Which style to use for printing backtraces.
     pub backtrace_style: BacktraceStyle,
-    /// Whether to enforce "strict provenance" rules. Enabling this means int2ptr casts return
-    /// pointers with an invalid provenance, i.e., not valid for any memory access.
-    pub strict_provenance: bool,
+    /// Which provenance to use for int2ptr casts
+    pub provenance_mode: ProvenanceMode,
     /// Whether to ignore any output by the program. This is helpful when debugging miri
     /// as its messages don't get intermingled with the program messages.
     pub mute_stdout_stderr: bool,
@@ -144,7 +143,7 @@ impl Default for MiriConfig {
             measureme_out: None,
             panic_on_unsupported: false,
             backtrace_style: BacktraceStyle::Short,
-            strict_provenance: false,
+            provenance_mode: ProvenanceMode::Legacy,
             mute_stdout_stderr: false,
         }
     }

src/helpers.rs

@@ -787,8 +787,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     fn mark_immutable(&mut self, mplace: &MemPlace<Tag>) {
         let this = self.eval_context_mut();
         // This got just allocated, so there definitely is a pointer here.
-        this.alloc_mark_immutable(mplace.ptr.into_pointer_or_addr().unwrap().provenance.alloc_id)
-            .unwrap();
+        let provenance = mplace.ptr.into_pointer_or_addr().unwrap().provenance;
+        this.alloc_mark_immutable(provenance.get_alloc_id().unwrap()).unwrap();
     }
 
     fn item_link_name(&self, def_id: DefId) -> Symbol {

src/intptrcast.rs

@@ -4,11 +4,25 @@ use std::collections::hash_map::Entry;
 use log::trace;
 use rand::Rng;
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_target::abi::{HasDataLayout, Size};
 
 use crate::*;
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ProvenanceMode {
+    /// Int2ptr casts return pointers with "wildcard" provenance
+    /// that basically matches that of all exposed pointers
+    /// (and SB tags, if enabled).
+    Permissive,
+    /// Int2ptr casts return pointers with an invalid provenance,
+    /// i.e., not valid for any memory access.
+    Strict,
+    /// Int2ptr casts determine the allocation they point to at cast time.
+    /// All allocations are considered exposed.
+    Legacy,
+}
+
 pub type GlobalState = RefCell<GlobalStateInner>;
 
 #[derive(Clone, Debug)]
@@ -21,35 +35,37 @@ pub struct GlobalStateInner {
     /// they do not have an `AllocExtra`.
     /// This is the inverse of `int_to_ptr_map`.
     base_addr: FxHashMap<AllocId, u64>,
+    /// Whether an allocation has been exposed or not. This cannot be put
+    /// into `AllocExtra` for the same reason as `base_addr`.
+    exposed: FxHashSet<AllocId>,
     /// This is used as a memory address when a new pointer is casted to an integer. It
     /// is always larger than any address that was previously made part of a block.
     next_base_addr: u64,
-    /// Whether to enforce "strict provenance" rules. Enabling this means int2ptr casts return
-    /// pointers with an invalid provenance, i.e., not valid for any memory access.
-    strict_provenance: bool,
+    /// The provenance to use for int2ptr casts
+    provenance_mode: ProvenanceMode,
 }
 
 impl GlobalStateInner {
     pub fn new(config: &MiriConfig) -> Self {
         GlobalStateInner {
             int_to_ptr_map: Vec::default(),
             base_addr: FxHashMap::default(),
+            exposed: FxHashSet::default(),
             next_base_addr: STACK_ADDR,
-            strict_provenance: config.strict_provenance,
+            provenance_mode: config.provenance_mode,
         }
     }
 }
 
 impl<'mir, 'tcx> GlobalStateInner {
-    pub fn ptr_from_addr(addr: u64, ecx: &MiriEvalContext<'mir, 'tcx>) -> Pointer<Option<Tag>> {
-        trace!("Casting 0x{:x} to a pointer", addr);
+    // Returns the exposed `AllocId` that corresponds to the specified addr,
+    // or `None` if the addr is out of bounds
+    fn alloc_id_from_addr(ecx: &MiriEvalContext<'mir, 'tcx>, addr: u64) -> Option<AllocId> {
         let global_state = ecx.machine.intptrcast.borrow();
-
-        if global_state.strict_provenance {
-            return Pointer::new(None, Size::from_bytes(addr));
-        }
+        assert!(global_state.provenance_mode != ProvenanceMode::Strict);
 
         let pos = global_state.int_to_ptr_map.binary_search_by_key(&addr, |(addr, _)| *addr);
+
         let alloc_id = match pos {
             Ok(pos) => Some(global_state.int_to_ptr_map[pos].1),
             Err(0) => None,
@@ -60,6 +76,7 @@ impl<'mir, 'tcx> GlobalStateInner {
                 // This never overflows because `addr >= glb`
                 let offset = addr - glb;
                 // If the offset exceeds the size of the allocation, don't use this `alloc_id`.
+
                 if offset
                     <= ecx
                         .get_alloc_size_and_align(alloc_id, AllocCheck::MaybeDead)
@@ -72,12 +89,65 @@ impl<'mir, 'tcx> GlobalStateInner {
                     None
                 }
             }
-        };
-        // Pointers created from integers are untagged.
-        Pointer::new(
-            alloc_id.map(|alloc_id| Tag { alloc_id, sb: SbTag::Untagged }),
-            Size::from_bytes(addr),
-        )
+        }?;
+
+        // In legacy mode, we consider all allocations exposed.
+        if global_state.provenance_mode == ProvenanceMode::Legacy
+            || global_state.exposed.contains(&alloc_id)
+        {
+            Some(alloc_id)
+        } else {
+            None
+        }
+    }
+
+    pub fn expose_addr(ecx: &MiriEvalContext<'mir, 'tcx>, alloc_id: AllocId) {
+        trace!("Exposing allocation id {:?}", alloc_id);
+
+        let mut global_state = ecx.machine.intptrcast.borrow_mut();
+        if global_state.provenance_mode == ProvenanceMode::Permissive {
+            global_state.exposed.insert(alloc_id);
+        }
+    }
+
+    pub fn ptr_from_addr_transmute(
+        ecx: &MiriEvalContext<'mir, 'tcx>,
+        addr: u64,
+    ) -> Pointer<Option<Tag>> {
+        trace!("Transmuting 0x{:x} to a pointer", addr);
+
+        let global_state = ecx.machine.intptrcast.borrow();
+
+        // In legacy mode, we have to support int2ptr transmutes,
+        // so just pretend they do the same thing as a cast.
+        if global_state.provenance_mode == ProvenanceMode::Legacy {
+            Self::ptr_from_addr_cast(ecx, addr)
+        } else {
+            Pointer::new(None, Size::from_bytes(addr))
+        }
+    }
+
+    pub fn ptr_from_addr_cast(
+        ecx: &MiriEvalContext<'mir, 'tcx>,
+        addr: u64,
+    ) -> Pointer<Option<Tag>> {
+        trace!("Casting 0x{:x} to a pointer", addr);
+
+        let global_state = ecx.machine.intptrcast.borrow();
+
+        if global_state.provenance_mode == ProvenanceMode::Strict {
+            Pointer::new(None, Size::from_bytes(addr))
+        } else if global_state.provenance_mode == ProvenanceMode::Legacy {
+            let alloc_id = Self::alloc_id_from_addr(ecx, addr);
+
+            Pointer::new(
+                alloc_id
+                    .map(|alloc_id| Tag::Concrete(ConcreteTag { alloc_id, sb: SbTag::Untagged })),
+                Size::from_bytes(addr),
+            )
+        } else {
+            Pointer::new(Some(Tag::Wildcard), Size::from_bytes(addr))
+        }
     }
 
     fn alloc_base_addr(ecx: &MiriEvalContext<'mir, 'tcx>, alloc_id: AllocId) -> u64 {
@@ -136,14 +206,27 @@ impl<'mir, 'tcx> GlobalStateInner {
         dl.overflowing_offset(base_addr, offset.bytes()).0
     }
 
-    pub fn abs_ptr_to_rel(ecx: &MiriEvalContext<'mir, 'tcx>, ptr: Pointer<Tag>) -> Size {
+    pub fn abs_ptr_to_rel(
+        ecx: &MiriEvalContext<'mir, 'tcx>,
+        ptr: Pointer<Tag>,
+    ) -> Option<(AllocId, Size)> {
         let (tag, addr) = ptr.into_parts(); // addr is absolute (Tag provenance)
-        let base_addr = GlobalStateInner::alloc_base_addr(ecx, tag.alloc_id);
+
+        let alloc_id = if let Tag::Concrete(concrete) = tag {
+            concrete.alloc_id
+        } else {
+            GlobalStateInner::alloc_id_from_addr(ecx, addr.bytes())?
+        };
+
+        let base_addr = GlobalStateInner::alloc_base_addr(ecx, alloc_id);
 
         // Wrapping "addr - base_addr"
         let dl = ecx.data_layout();
         let neg_base_addr = (base_addr as i64).wrapping_neg();
-        Size::from_bytes(dl.overflowing_signed_offset(addr.bytes(), neg_base_addr).0)
+        Some((
+            alloc_id,
+            Size::from_bytes(dl.overflowing_signed_offset(addr.bytes(), neg_base_addr).0),
+        ))
     }
 
     /// Shifts `addr` to make it aligned with `align` by rounding `addr` to the smallest multiple

src/lib.rs

@@ -78,9 +78,10 @@ pub use crate::eval::{
     create_ecx, eval_entry, AlignmentCheck, BacktraceStyle, IsolatedOp, MiriConfig, RejectOpWith,
 };
 pub use crate::helpers::EvalContextExt as HelpersEvalContextExt;
+pub use crate::intptrcast::ProvenanceMode;
 pub use crate::machine::{
-    AllocExtra, Evaluator, FrameData, MiriEvalContext, MiriEvalContextExt, MiriMemoryKind, Tag,
-    NUM_CPUS, PAGE_SIZE, STACK_ADDR, STACK_SIZE,
+    AllocExtra, ConcreteTag, Evaluator, FrameData, MiriEvalContext, MiriEvalContextExt,
+    MiriMemoryKind, Tag, NUM_CPUS, PAGE_SIZE, STACK_ADDR, STACK_SIZE,
 };
 pub use crate::mono_hash_map::MonoHashMap;
 pub use crate::operator::EvalContextExt as OperatorEvalContextExt;

src/machine.rs

@@ -126,16 +126,22 @@ impl fmt::Display for MiriMemoryKind {
 
 /// Pointer provenance (tag).
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct Tag {
+pub enum Tag {
+    Concrete(ConcreteTag),
+    Wildcard,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct ConcreteTag {
     pub alloc_id: AllocId,
     /// Stacked Borrows tag.
     pub sb: SbTag,
 }
 
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 static_assert_size!(Pointer<Tag>, 24);
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-static_assert_size!(Pointer<Option<Tag>>, 24);
+// #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+// static_assert_size!(Pointer<Option<Tag>>, 24);
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 static_assert_size!(ScalarMaybeUninit<Tag>, 32);
 
@@ -149,18 +155,31 @@ impl Provenance for Tag {
     fn fmt(ptr: &Pointer<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let (tag, addr) = ptr.into_parts(); // address is absolute
         write!(f, "0x{:x}", addr.bytes())?;
-        // Forward `alternate` flag to `alloc_id` printing.
-        if f.alternate() {
-            write!(f, "[{:#?}]", tag.alloc_id)?;
-        } else {
-            write!(f, "[{:?}]", tag.alloc_id)?;
+
+        match tag {
+            Tag::Concrete(tag) => {
+                // Forward `alternate` flag to `alloc_id` printing.
+                if f.alternate() {
+                    write!(f, "[{:#?}]", tag.alloc_id)?;
+                } else {
+                    write!(f, "[{:?}]", tag.alloc_id)?;
+                }
+                // Print Stacked Borrows tag.
+                write!(f, "{:?}", tag.sb)?;
+            }
+            Tag::Wildcard => {
+                write!(f, "[Wildcard]")?;
+            }
         }
-        // Print Stacked Borrows tag.
-        write!(f, "{:?}", tag.sb)
+
+        Ok(())
     }
 
     fn get_alloc_id(self) -> Option<AllocId> {
-        Some(self.alloc_id)
+        match self {
+            Tag::Concrete(concrete) => Some(concrete.alloc_id),
+            Tag::Wildcard => None,
+        }
     }
 }
 
@@ -609,30 +628,41 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for Evaluator<'mir, 'tcx> {
         } else {
             SbTag::Untagged
         };
-        Pointer::new(Tag { alloc_id: ptr.provenance, sb: sb_tag }, Size::from_bytes(absolute_addr))
+        Pointer::new(
+            Tag::Concrete(ConcreteTag { alloc_id: ptr.provenance, sb: sb_tag }),
+            Size::from_bytes(absolute_addr),
+        )
     }
 
     #[inline(always)]
     fn ptr_from_addr_cast(
         ecx: &MiriEvalContext<'mir, 'tcx>,
         addr: u64,
     ) -> Pointer<Option<Self::PointerTag>> {
-        intptrcast::GlobalStateInner::ptr_from_addr(addr, ecx)
+        intptrcast::GlobalStateInner::ptr_from_addr_cast(ecx, addr)
     }
 
     #[inline(always)]
     fn ptr_from_addr_transmute(
         ecx: &MiriEvalContext<'mir, 'tcx>,
         addr: u64,
     ) -> Pointer<Option<Self::PointerTag>> {
-        Self::ptr_from_addr_cast(ecx, addr)
+        intptrcast::GlobalStateInner::ptr_from_addr_transmute(ecx, addr)
     }
 
     #[inline(always)]
     fn expose_ptr(
-        _ecx: &mut InterpCx<'mir, 'tcx, Self>,
-        _ptr: Pointer<Self::PointerTag>,
+        ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        ptr: Pointer<Self::PointerTag>,
     ) -> InterpResult<'tcx> {
+        let tag = ptr.provenance;
+
+        if let Tag::Concrete(concrete) = tag {
+            intptrcast::GlobalStateInner::expose_addr(ecx, concrete.alloc_id);
+        }
+
+        // No need to do anything for wildcard pointers as
+        // their provenances have already been previously exposed.
         Ok(())
     }
 
@@ -643,7 +673,13 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for Evaluator<'mir, 'tcx> {
         ptr: Pointer<Self::PointerTag>,
     ) -> Option<(AllocId, Size, Self::TagExtra)> {
         let rel = intptrcast::GlobalStateInner::abs_ptr_to_rel(ecx, ptr);
-        Some((ptr.provenance.alloc_id, rel, ptr.provenance.sb))
+
+        let sb = match ptr.provenance {
+            Tag::Concrete(ConcreteTag { sb, .. }) => sb,
+            Tag::Wildcard => SbTag::Untagged,
+        };
+
+        rel.map(|(alloc_id, size)| (alloc_id, size, sb))
     }
 
     #[inline(always)]