Add precondition checks to ptr::offset, ptr::add, ptr::sub

rust-lang · Oct 7, 2024 · 6d246e4 · 6d246e4
1 parent 7caad69
commit 6d246e4
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Showing 13 changed files with 277 additions and 43 deletions.
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
@@ -395,6 +395,36 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_offset_nowrap(this: *const (), count: isize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: isize, size: usize) -> bool {
+                // We know `size <= isize::MAX` so the `as` cast here is not lossy.
+                let Some(byte_offset) = count.checked_mul(size as isize) else {
+                    return false;
+                };
+                let (_, overflow) = this.addr().overflowing_add_signed(byte_offset);
+                !overflow
+            }
+
+            const fn comptime(_: *const (), _: isize, _: usize) -> bool {
+                true
+            }
+
+            // We can use const_eval_select here because this is only for UB checks.
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::offset requires the address calculation to not overflow",
+            (
+                this: *const () = self as *const (),
+                count: isize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_offset_nowrap(this, count, size)
+        );
+
         // SAFETY: the caller must uphold the safety contract for `offset`.
         unsafe { intrinsics::offset(self, count) }
     }
@@ -726,7 +756,6 @@ impl<T: ?Sized> *const T {
                 true
             }
 
-            #[allow(unused_unsafe)]
             intrinsics::const_eval_select((this, origin), comptime, runtime)
         }
 
@@ -858,6 +887,34 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: usize, size: usize) -> bool {
+                let Some(byte_offset) = count.checked_mul(size) else {
+                    return false;
+                };
+                let (_, overflow) = this.addr().overflowing_add(byte_offset);
+                byte_offset <= (isize::MAX as usize) && !overflow
+            }
+
+            const fn comptime(_: *const (), _: usize, _: usize) -> bool {
+                true
+            }
+
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::add requires that the address calculation does not overflow",
+            (
+                this: *const () = self as *const (),
+                count: usize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_add_nowrap(this, count, size)
+        );
+
         // SAFETY: the caller must uphold the safety contract for `offset`.
         unsafe { intrinsics::offset(self, count) }
     }
@@ -936,14 +993,41 @@ impl<T: ?Sized> *const T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: usize, size: usize) -> bool {
+                let Some(byte_offset) = count.checked_mul(size) else {
+                    return false;
+                };
+                byte_offset <= (isize::MAX as usize) && this.addr() >= byte_offset
+            }
+
+            const fn comptime(_: *const (), _: usize, _: usize) -> bool {
+                true
+            }
+
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::sub requires that the address calculation does not overflow",
+            (
+                this: *const () = self as *const (),
+                count: usize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_sub_nowrap(this, count, size)
+        );
+
         if T::IS_ZST {
             // Pointer arithmetic does nothing when the pointee is a ZST.
             self
         } else {
             // SAFETY: the caller must uphold the safety contract for `offset`.
             // Because the pointee is *not* a ZST, that means that `count` is
             // at most `isize::MAX`, and thus the negation cannot overflow.
-            unsafe { self.offset((count as isize).unchecked_neg()) }
+            unsafe { intrinsics::offset(self, intrinsics::unchecked_sub(0, count as isize)) }
         }
     }
 

diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
@@ -393,6 +393,37 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_offset_nowrap(this: *const (), count: isize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: isize, size: usize) -> bool {
+                // `size` is the size of a Rust type, so we know that
+                // `size <= isize::MAX` and thus `as` cast here is not lossy.
+                let Some(byte_offset) = count.checked_mul(size as isize) else {
+                    return false;
+                };
+                let (_, overflow) = this.addr().overflowing_add_signed(byte_offset);
+                !overflow
+            }
+
+            const fn comptime(_: *const (), _: isize, _: usize) -> bool {
+                true
+            }
+
+            // We can use const_eval_select here because this is only for UB checks.
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::offset requires the address calculation to not overflow",
+            (
+                this: *const () = self as *const (),
+                count: isize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_offset_nowrap(this, count, size)
+        );
+
         // SAFETY: the caller must uphold the safety contract for `offset`.
         // The obtained pointer is valid for writes since the caller must
         // guarantee that it points to the same allocated object as `self`.
@@ -940,6 +971,34 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: usize, size: usize) -> bool {
+                let Some(byte_offset) = count.checked_mul(size) else {
+                    return false;
+                };
+                let (_, overflow) = this.addr().overflowing_add(byte_offset);
+                byte_offset <= (isize::MAX as usize) && !overflow
+            }
+
+            const fn comptime(_: *const (), _: usize, _: usize) -> bool {
+                true
+            }
+
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::add requires that the address calculation does not overflow",
+            (
+                this: *const () = self as *const (),
+                count: usize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_add_nowrap(this, count, size)
+        );
+
         // SAFETY: the caller must uphold the safety contract for `offset`.
         unsafe { intrinsics::offset(self, count) }
     }
@@ -1018,14 +1077,41 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
+        #[inline]
+        const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
+            #[inline]
+            fn runtime(this: *const (), count: usize, size: usize) -> bool {
+                let Some(byte_offset) = count.checked_mul(size) else {
+                    return false;
+                };
+                byte_offset <= (isize::MAX as usize) && this.addr() >= byte_offset
+            }
+
+            const fn comptime(_: *const (), _: usize, _: usize) -> bool {
+                true
+            }
+
+            intrinsics::const_eval_select((this, count, size), comptime, runtime)
+        }
+
+        ub_checks::assert_unsafe_precondition!(
+            check_language_ub,
+            "ptr::sub requires that the address calculation does not overflow",
+            (
+                this: *const () = self as *const (),
+                count: usize = count,
+                size: usize = size_of::<T>(),
+            ) => runtime_sub_nowrap(this, count, size)
+        );
+
         if T::IS_ZST {
             // Pointer arithmetic does nothing when the pointee is a ZST.
             self
         } else {
             // SAFETY: the caller must uphold the safety contract for `offset`.
             // Because the pointee is *not* a ZST, that means that `count` is
             // at most `isize::MAX`, and thus the negation cannot overflow.
-            unsafe { self.offset((count as isize).unchecked_neg()) }
+            unsafe { intrinsics::offset(self, intrinsics::unchecked_sub(0, count as isize)) }
         }
     }
 

diff --git a/tests/codegen/option-as-slice.rs b/tests/codegen/option-as-slice.rs
@@ -14,7 +14,9 @@ pub fn u64_opt_as_slice(o: &Option<u64>) -> &[u64] {
     // CHECK-NOT: br
     // CHECK-NOT: switch
     // CHECK-NOT: icmp
-    // CHECK: %[[LEN:.+]] = load i64,{{.+}} !range ![[META_U64:.+]], !noundef
+    // CHECK: %[[LEN:.+]] = load i64
+    // CHECK-SAME: !range ![[META_U64:[0-9]+]],
+    // CHECK-SAME: !noundef
     // CHECK-NOT: select
     // CHECK-NOT: br
     // CHECK-NOT: switch
@@ -51,7 +53,9 @@ pub fn u8_opt_as_slice(o: &Option<u8>) -> &[u8] {
     // CHECK-NOT: br
     // CHECK-NOT: switch
     // CHECK-NOT: icmp
-    // CHECK: %[[TAG:.+]] = load i8,{{.+}} !range ![[META_U8:.+]], !noundef
+    // CHECK: %[[TAG:.+]] = load i8
+    // CHECK-SAME: !range ![[META_U8:[0-9]+]],
+    // CHECK-SAME: !noundef
     // CHECK: %[[LEN:.+]] = zext{{.*}} i8 %[[TAG]] to i64
     // CHECK-NOT: select
     // CHECK-NOT: br

diff --git a/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-abort.mir b/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-abort.mir
@@ -10,12 +10,18 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
         scope 2 (inlined std::ptr::const_ptr::<impl *const [u32]>::cast::<u8>) {
         }
         scope 3 (inlined std::ptr::const_ptr::<impl *const u8>::add) {
+            scope 4 (inlined core::ub_checks::check_language_ub) {
+                scope 5 (inlined core::ub_checks::check_language_ub::runtime) {
+                }
+            }
+            scope 6 (inlined std::mem::size_of::<u8>) {
+            }
         }
-        scope 4 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<[u32]>) {
+        scope 7 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<[u32]>) {
             let mut _5: usize;
-            scope 5 (inlined std::ptr::metadata::<[u32]>) {
+            scope 8 (inlined std::ptr::metadata::<[u32]>) {
             }
-            scope 6 (inlined std::ptr::from_raw_parts::<[u32], ()>) {
+            scope 9 (inlined std::ptr::from_raw_parts::<[u32], ()>) {
             }
         }
     }

diff --git a/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-unwind.mir b/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-unwind.mir
@@ -10,12 +10,18 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
         scope 2 (inlined std::ptr::const_ptr::<impl *const [u32]>::cast::<u8>) {
         }
         scope 3 (inlined std::ptr::const_ptr::<impl *const u8>::add) {
+            scope 4 (inlined core::ub_checks::check_language_ub) {
+                scope 5 (inlined core::ub_checks::check_language_ub::runtime) {
+                }
+            }
+            scope 6 (inlined std::mem::size_of::<u8>) {
+            }
         }
-        scope 4 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<[u32]>) {
+        scope 7 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<[u32]>) {
             let mut _5: usize;
-            scope 5 (inlined std::ptr::metadata::<[u32]>) {
+            scope 8 (inlined std::ptr::metadata::<[u32]>) {
             }
-            scope 6 (inlined std::ptr::from_raw_parts::<[u32], ()>) {
+            scope 9 (inlined std::ptr::from_raw_parts::<[u32], ()>) {
             }
         }
     }

diff --git a/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-abort.mir b/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-abort.mir
@@ -10,11 +10,17 @@ fn demo_byte_add_thin(_1: *const u32, _2: usize) -> *const u32 {
         scope 2 (inlined std::ptr::const_ptr::<impl *const u32>::cast::<u8>) {
         }
         scope 3 (inlined std::ptr::const_ptr::<impl *const u8>::add) {
+            scope 4 (inlined core::ub_checks::check_language_ub) {
+                scope 5 (inlined core::ub_checks::check_language_ub::runtime) {
+                }
+            }
+            scope 6 (inlined std::mem::size_of::<u8>) {
+            }
         }
-        scope 4 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<u32>) {
-            scope 5 (inlined std::ptr::metadata::<u32>) {
+        scope 7 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<u32>) {
+            scope 8 (inlined std::ptr::metadata::<u32>) {
             }
-            scope 6 (inlined std::ptr::from_raw_parts::<u32, ()>) {
+            scope 9 (inlined std::ptr::from_raw_parts::<u32, ()>) {
             }
         }
     }

diff --git a/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-unwind.mir b/tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-unwind.mir
@@ -10,11 +10,17 @@ fn demo_byte_add_thin(_1: *const u32, _2: usize) -> *const u32 {
         scope 2 (inlined std::ptr::const_ptr::<impl *const u32>::cast::<u8>) {
         }
         scope 3 (inlined std::ptr::const_ptr::<impl *const u8>::add) {
+            scope 4 (inlined core::ub_checks::check_language_ub) {
+                scope 5 (inlined core::ub_checks::check_language_ub::runtime) {
+                }
+            }
+            scope 6 (inlined std::mem::size_of::<u8>) {
+            }
         }
-        scope 4 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<u32>) {
-            scope 5 (inlined std::ptr::metadata::<u32>) {
+        scope 7 (inlined std::ptr::const_ptr::<impl *const u8>::with_metadata_of::<u32>) {
+            scope 8 (inlined std::ptr::metadata::<u32>) {
             }
-            scope 6 (inlined std::ptr::from_raw_parts::<u32, ()>) {
+            scope 9 (inlined std::ptr::from_raw_parts::<u32, ()>) {
             }
         }
     }