Auto merge of #2046 - RalfJung:very-strict, r=RalfJung

make strict-provenance imply check-number-validity

I feel like Miri not catching [this example](rust-lang/unsafe-code-guidelines#286 (comment)) with strict provenance checking enabled is surprising.

OTOH, Miri suddenly complaining about uninit data in integers with `-Zmiri-strict-provenance` also might be surprising. Which one is more surprising? I don't know. We *could* go out of our way and have a mode where uninit integers are okay but provenance is not, but I am not sure if that is truly worth it. It'd be quite annoying to implement.

Author: bors

README.md

@@ -297,7 +297,8 @@ environment variable:
 * `-Zmiri-strict-provenance` enables [strict
   provenance](https://github.com/rust-lang/rust/issues/95228) checking in Miri. This means that
   casting an integer to a pointer yields a result with 'invalid' provenance, i.e., with provenance
-  that cannot be used for any memory access. Also implies `-Zmiri-tag-raw-pointers`.
+  that cannot be used for any memory access. Also implies `-Zmiri-tag-raw-pointers` and
+  `-Zmiri-check-number-validity`.
 * `-Zmiri-symbolic-alignment-check` makes the alignment check more strict.  By
   default, alignment is checked by casting the pointer to an integer, and making
   sure that is a multiple of the alignment.  This can lead to cases where a

src/bin/miri.rs

@@ -366,6 +366,7 @@ fn main() {
                 "-Zmiri-strict-provenance" => {
                     miri_config.strict_provenance = true;
                     miri_config.tag_raw = true;
+                    miri_config.check_number_validity = true;
                 }
                 "-Zmiri-track-raw-pointers" => {
                     eprintln!(

tests/compile-fail/strict_provenance_transmute.rs

@@ -0,0 +1,27 @@
+// compile-flags: -Zmiri-strict-provenance
+#![feature(strict_provenance)]
+
+use std::mem;
+
+// This is the example from
+// <https://github.com/rust-lang/unsafe-code-guidelines/issues/286#issuecomment-1085144431>.
+
+unsafe fn deref(left: *const u8, right: *const u8) {
+    let left_int: usize = mem::transmute(left); //~ERROR expected initialized plain (non-pointer) bytes
+    let right_int: usize = mem::transmute(right);
+    if left_int == right_int {
+        // The compiler is allowed to replace `left_int` by `right_int` here...
+        let left_ptr: *const u8 = mem::transmute(left_int);
+        // ...which however means here it could be dereferencing the wrong pointer.
+        let _val = *left_ptr;
+    }
+}
+
+fn main() {
+    let ptr1 = &0u8 as *const u8;
+    let ptr2 = &1u8 as *const u8;
+    unsafe {
+        // Two pointers with the same address but different provenance.
+        deref(ptr1, ptr2.with_addr(ptr1.addr()));
+    }
+}

tests/run-pass/btreemap.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 #![feature(btree_drain_filter)]
 use std::collections::{BTreeMap, BTreeSet};
 use std::mem;

tests/run-pass/concurrency/sync.rs

@@ -1,5 +1,5 @@
 // ignore-windows: Concurrency on Windows is not supported yet.
-// compile-flags: -Zmiri-disable-isolation -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-disable-isolation -Zmiri-strict-provenance
 
 use std::sync::{Arc, Barrier, Condvar, Mutex, Once, RwLock};
 use std::thread;

tests/run-pass/concurrency/thread_locals.rs

@@ -1,5 +1,5 @@
 // ignore-windows: Concurrency on Windows is not supported yet.
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 
 //! The main purpose of this test is to check that if we take a pointer to
 //! thread's `t1` thread-local `A` and send it to another thread `t2`,

tests/run-pass/rc.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 #![feature(new_uninit)]
 #![feature(get_mut_unchecked)]
 

tests/run-pass/slices.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 #![feature(new_uninit)]
 #![feature(slice_as_chunks)]
 #![feature(slice_partition_dedup)]

tests/run-pass/strings.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 
 fn empty() -> &'static str {
     ""

tests/run-pass/vec.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmiri-strict-provenance -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 // Gather all references from a mutable iterator and make sure Miri notices if
 // using them is dangerous.
 fn test_all_refs<'a, T: 'a>(dummy: &mut T, iter: impl Iterator<Item = &'a mut T>) {