Rollup merge of #82061 - RalfJung:ctfe-read-pointer-as-bytes, r=oli-obk

CTFE validation: catch ReadPointerAsBytes and better error

r? ``@oli-obk``
Fixes #79690
Cc rust-lang/miri#1706

Author: jonas-schievink

compiler/rustc_mir/src/interpret/validity.rs

@@ -21,7 +21,7 @@ use std::hash::Hash;
 
 use super::{
     CheckInAllocMsg, GlobalAlloc, InterpCx, InterpResult, MPlaceTy, Machine, MemPlaceMeta, OpTy,
-    ValueVisitor,
+    ScalarMaybeUninit, ValueVisitor,
 };
 
 macro_rules! throw_validation_failure {
@@ -378,7 +378,11 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         value: OpTy<'tcx, M::PointerTag>,
         kind: &str,
     ) -> InterpResult<'tcx> {
-        let value = self.ecx.read_immediate(value)?;
+        let value = try_validation!(
+            self.ecx.read_immediate(value),
+            self.path,
+            err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
+        );
         // Handle wide pointers.
         // Check metadata early, for better diagnostics
         let place = try_validation!(
@@ -485,6 +489,17 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         Ok(())
     }
 
+    fn read_scalar(
+        &self,
+        op: OpTy<'tcx, M::PointerTag>,
+    ) -> InterpResult<'tcx, ScalarMaybeUninit<M::PointerTag>> {
+        Ok(try_validation!(
+            self.ecx.read_scalar(op),
+            self.path,
+            err_unsup!(ReadPointerAsBytes) => { "(potentially part of) a pointer" } expected { "plain (non-pointer) bytes" },
+        ))
+    }
+
     /// Check if this is a value of primitive type, and if yes check the validity of the value
     /// at that type.  Return `true` if the type is indeed primitive.
     fn try_visit_primitive(
@@ -495,7 +510,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         let ty = value.layout.ty;
         match ty.kind() {
             ty::Bool => {
-                let value = self.ecx.read_scalar(value)?;
+                let value = self.read_scalar(value)?;
                 try_validation!(
                     value.to_bool(),
                     self.path,
@@ -505,7 +520,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 Ok(true)
             }
             ty::Char => {
-                let value = self.ecx.read_scalar(value)?;
+                let value = self.read_scalar(value)?;
                 try_validation!(
                     value.to_char(),
                     self.path,
@@ -515,11 +530,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 Ok(true)
             }
             ty::Float(_) | ty::Int(_) | ty::Uint(_) => {
-                let value = try_validation!(
-                    self.ecx.read_scalar(value),
-                    self.path,
-                    err_unsup!(ReadPointerAsBytes) => { "read of part of a pointer" },
-                );
+                let value = self.read_scalar(value)?;
                 // NOTE: Keep this in sync with the array optimization for int/float
                 // types below!
                 if self.ctfe_mode.is_some() {
@@ -541,9 +552,10 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 // actually enforce the strict rules for raw pointers (mostly because
                 // that lets us re-use `ref_to_mplace`).
                 let place = try_validation!(
-                    self.ecx.ref_to_mplace(self.ecx.read_immediate(value)?),
+                    self.ecx.read_immediate(value).and_then(|i| self.ecx.ref_to_mplace(i)),
                     self.path,
                     err_ub!(InvalidUninitBytes(None)) => { "uninitialized raw pointer" },
+                    err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
                 );
                 if place.layout.is_unsized() {
                     self.check_wide_ptr_meta(place.meta, place.layout)?;
@@ -569,9 +581,13 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 Ok(true)
             }
             ty::FnPtr(_sig) => {
-                let value = self.ecx.read_scalar(value)?;
+                let value = try_validation!(
+                    self.ecx.read_immediate(value),
+                    self.path,
+                    err_unsup!(ReadPointerAsBytes) => { "part of a pointer" } expected { "a proper pointer or integer value" },
+                );
                 let _fn = try_validation!(
-                    value.check_init().and_then(|ptr| self.ecx.memory.get_fn(ptr)),
+                    value.to_scalar().and_then(|ptr| self.ecx.memory.get_fn(ptr)),
                     self.path,
                     err_ub!(DanglingIntPointer(..)) |
                     err_ub!(InvalidFunctionPointer(..)) |
@@ -615,7 +631,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         op: OpTy<'tcx, M::PointerTag>,
         scalar_layout: &Scalar,
     ) -> InterpResult<'tcx> {
-        let value = self.ecx.read_scalar(op)?;
+        let value = self.read_scalar(op)?;
         let valid_range = &scalar_layout.valid_range;
         let (lo, hi) = valid_range.clone().into_inner();
         // Determine the allowed range

src/test/ui/consts/issue-79690.stderr

@@ -2,7 +2,7 @@ error[E0080]: it is undefined behavior to use this value
   --> $DIR/issue-79690.rs:29:1
    |
 LL | const G: Fat = unsafe { Transmute { t: FOO }.u };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered read of part of a pointer at .1.<deref>.size.foo
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered (potentially part of) a pointer at .1.<deref>.size.foo, but expected plain (non-pointer) bytes
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.