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…=Nilstrieb

Improve `invalid_reference_casting` lint

This PR is a follow-up to rust-lang#111567 and rust-lang#113422.

This PR does multiple things:
 - First it adds support for deferred de-reference, the goal is to support code like this, where the casting and de-reference are not done on the same expression
    ```rust
    let myself = self as *const Self as *mut Self;
    *myself = Self::Ready(value);
    ```
 - Second it does not lint anymore on SB/TB UB code by only checking assignments (`=`, `+=`, ...) and creation of mutable references `&mut *`
 - Thirdly it greatly improves the diagnostics in particular for cast from `&mut` to `&mut` or assignments
 - ~~And lastly it renames the lint from `cast_ref_to_mut` to `invalid_reference_casting` which is more consistent with the ["rules"](rust-lang/rust-clippy#2845) and also more consistent with what the lint checks~~ *rust-lang#113422

This PR is best reviewed commit by commit.

r? compiler
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bors committed Aug 2, 2023
2 parents 64ad036 + 507d497 commit d170833
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6 changes: 5 additions & 1 deletion compiler/rustc_lint/messages.ftl
Original file line number Diff line number Diff line change
Expand Up @@ -318,7 +318,11 @@ lint_invalid_nan_comparisons_eq_ne = incorrect NaN comparison, NaN cannot be dir
lint_invalid_nan_comparisons_lt_le_gt_ge = incorrect NaN comparison, NaN is not orderable
lint_invalid_reference_casting = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
lint_invalid_reference_casting_assign_to_ref = assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
.label = casting happend here
lint_invalid_reference_casting_borrow_as_mut = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
.label = casting happend here
lint_lintpass_by_hand = implementing `LintPass` by hand
.help = try using `declare_lint_pass!` or `impl_lint_pass!` instead
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_lint/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,7 @@ late_lint_methods!(
BoxPointers: BoxPointers,
PathStatements: PathStatements,
LetUnderscore: LetUnderscore,
InvalidReferenceCasting: InvalidReferenceCasting,
InvalidReferenceCasting: InvalidReferenceCasting::default(),
// Depends on referenced function signatures in expressions
UnusedResults: UnusedResults,
NonUpperCaseGlobals: NonUpperCaseGlobals,
Expand Down
14 changes: 12 additions & 2 deletions compiler/rustc_lint/src/lints.rs
Original file line number Diff line number Diff line change
Expand Up @@ -745,8 +745,18 @@ pub enum InvalidFromUtf8Diag {

// reference_casting.rs
#[derive(LintDiagnostic)]
#[diag(lint_invalid_reference_casting)]
pub struct InvalidReferenceCastingDiag;
pub enum InvalidReferenceCastingDiag {
#[diag(lint_invalid_reference_casting_borrow_as_mut)]
BorrowAsMut {
#[label]
orig_cast: Option<Span>,
},
#[diag(lint_invalid_reference_casting_assign_to_ref)]
AssignToRef {
#[label]
orig_cast: Option<Span>,
},
}

// hidden_unicode_codepoints.rs
#[derive(LintDiagnostic)]
Expand Down
113 changes: 85 additions & 28 deletions compiler/rustc_lint/src/reference_casting.rs
Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
use rustc_ast::Mutability;
use rustc_hir::{Expr, ExprKind, MutTy, TyKind, UnOp};
use rustc_middle::ty;
use rustc_span::sym;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, QPath, StmtKind, UnOp};
use rustc_middle::ty::{self, TypeAndMut};
use rustc_span::{sym, Span};

use crate::{lints::InvalidReferenceCastingDiag, LateContext, LateLintPass, LintContext};

Expand All @@ -12,7 +13,6 @@ declare_lint! {
/// ### Example
///
/// ```rust,compile_fail
/// # #![deny(invalid_reference_casting)]
/// fn x(r: &i32) {
/// unsafe {
/// *(r as *const i32 as *mut i32) += 1;
Expand All @@ -30,46 +30,103 @@ declare_lint! {
/// `UnsafeCell` is the only way to obtain aliasable data that is considered
/// mutable.
INVALID_REFERENCE_CASTING,
Allow,
Deny,
"casts of `&T` to `&mut T` without interior mutability"
}

declare_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
#[derive(Default)]
pub struct InvalidReferenceCasting {
casted: FxHashMap<HirId, Span>,
}

impl_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);

impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
let ExprKind::Unary(UnOp::Deref, e) = &expr.kind else {
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx rustc_hir::Stmt<'tcx>) {
let StmtKind::Local(local) = stmt.kind else {
return;
};
let Local { init: Some(init), els: None, .. } = local else {
return;
};

let e = e.peel_blocks();
let e = if let ExprKind::Cast(e, t) = e.kind
&& let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind {
e
} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
if is_cast_from_const_to_mut(cx, init) {
self.casted.insert(local.pat.hir_id, init.span);
}
}

fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
// &mut <expr>
let inner = if let ExprKind::AddrOf(_, Mutability::Mut, expr) = expr.kind {
expr
// <expr> = ...
} else if let ExprKind::Assign(expr, _, _) = expr.kind {
expr
// <expr> += ...
} else if let ExprKind::AssignOp(_, expr, _) = expr.kind {
expr
} else {
return;
};

let e = e.peel_blocks();
let e = if let ExprKind::Cast(e, t) = e.kind
&& let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind {
e
} else if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::ptr_from_ref, def_id) {
arg
let ExprKind::Unary(UnOp::Deref, e) = &inner.kind else {
return;
};

let orig_cast = if is_cast_from_const_to_mut(cx, e) {
None
} else if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind
&& let Res::Local(hir_id) = &path.res
&& let Some(orig_cast) = self.casted.get(hir_id) {
Some(*orig_cast)
} else {
return;
};

let e = e.peel_blocks();
if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind() {
cx.emit_spanned_lint(INVALID_REFERENCE_CASTING, expr.span, InvalidReferenceCastingDiag);
}
cx.emit_spanned_lint(
INVALID_REFERENCE_CASTING,
expr.span,
if matches!(expr.kind, ExprKind::AddrOf(..)) {
InvalidReferenceCastingDiag::BorrowAsMut { orig_cast }
} else {
InvalidReferenceCastingDiag::AssignToRef { orig_cast }
},
);
}
}

fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
let e = e.peel_blocks();

// <expr> as *mut ...
let e = if let ExprKind::Cast(e, t) = e.kind
&& let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(t.hir_id).kind() {
e
// <expr>.cast_mut()
} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
expr
} else {
return false;
};

let e = e.peel_blocks();

// <expr> as *const ...
let e = if let ExprKind::Cast(e, t) = e.kind
&& let ty::RawPtr(TypeAndMut { mutbl: Mutability::Not, .. }) = cx.typeck_results().node_type(t.hir_id).kind() {
e
// ptr::from_ref(<expr>)
} else if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::ptr_from_ref, def_id) {
arg
} else {
return false;
};

let e = e.peel_blocks();
matches!(cx.typeck_results().node_type(e.hir_id).kind(), ty::Ref(_, _, Mutability::Not))
}
3 changes: 2 additions & 1 deletion library/core/src/cell.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1893,7 +1893,8 @@ impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
/// on an _exclusive_ `UnsafeCell<T>`. Even though `T` and `UnsafeCell<T>` have the
/// same memory layout, the following is not allowed and undefined behavior:
///
/// ```rust,no_run
#[cfg_attr(bootstrap, doc = "```rust,no_run")]
#[cfg_attr(not(bootstrap), doc = "```rust,compile_fail")]
/// # use std::cell::UnsafeCell;
/// unsafe fn not_allowed<T>(ptr: &UnsafeCell<T>) -> &mut T {
/// let t = ptr as *const UnsafeCell<T> as *mut T;
Expand Down
2 changes: 2 additions & 0 deletions src/tools/miri/tests/fail/both_borrows/illegal_write1.rs
Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
//@revisions: stack tree
//@[tree]compile-flags: -Zmiri-tree-borrows

#![allow(invalid_reference_casting)]

fn main() {
let target = Box::new(42); // has an implicit raw
let xref = &*target;
Expand Down
2 changes: 2 additions & 0 deletions src/tools/miri/tests/fail/stacked_borrows/illegal_write3.rs
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
#![allow(invalid_reference_casting)]

fn main() {
let target = 42;
// Make sure raw ptr with raw tag cannot mutate frozen location without breaking the shared ref.
Expand Down
1 change: 1 addition & 0 deletions tests/ui/const-generics/issues/issue-100313.rs
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ impl <const B: &'static bool> T<B> {
unsafe {
*(B as *const bool as *mut bool) = false;
//~^ ERROR evaluation of constant value failed [E0080]
//~| ERROR assigning to `&T` is undefined behavior
}
}
}
Expand Down
12 changes: 10 additions & 2 deletions tests/ui/const-generics/issues/issue-100313.stderr
Original file line number Diff line number Diff line change
@@ -1,3 +1,11 @@
error: assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
--> $DIR/issue-100313.rs:10:13
|
LL | *(B as *const bool as *mut bool) = false;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[deny(invalid_reference_casting)]` on by default

error[E0080]: evaluation of constant value failed
--> $DIR/issue-100313.rs:10:13
|
Expand All @@ -10,11 +18,11 @@ note: inside `T::<&true>::set_false`
LL | *(B as *const bool as *mut bool) = false;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: inside `_`
--> $DIR/issue-100313.rs:18:5
--> $DIR/issue-100313.rs:19:5
|
LL | x.set_false();
| ^^^^^^^^^^^^^

error: aborting due to previous error
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0080`.
94 changes: 57 additions & 37 deletions tests/ui/lint/reference_casting.rs
Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
// check-fail

#![feature(ptr_from_ref)]
#![deny(invalid_reference_casting)]

extern "C" {
// N.B., mutability can be easily incorrect in FFI calls -- as
Expand All @@ -10,42 +9,63 @@ extern "C" {
fn int_ffi(c: *mut i32);
}

fn main() {
unsafe fn ref_to_mut() {
let num = &3i32;

let _num = &mut *(num as *const i32 as *mut i32);
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *(num as *const i32).cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *std::ptr::from_ref(num).cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *std::ptr::from_ref({ num }).cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *{ std::ptr::from_ref(num) }.cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *(std::ptr::from_ref({ num }) as *mut i32);
//~^ ERROR casting `&T` to `&mut T` is undefined behavior

let deferred = num as *const i32 as *mut i32;
let _num = &mut *deferred;
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
}

unsafe fn assign_to_ref() {
let s = String::from("Hello");
let a = &s;
unsafe {
let num = &3i32;
let mut_num = &mut 3i32;

(*(a as *const _ as *mut String)).push_str(" world");
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*(a as *const _ as *mut _) = String::from("Replaced");
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*(a as *const _ as *mut String) += " world";
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *(num as *const i32 as *mut i32);
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = &mut *(num as *const i32).cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
let _num = *{ num as *const i32 }.cast_mut();
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*std::ptr::from_ref(num).cast_mut() += 1;
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*std::ptr::from_ref({ num }).cast_mut() += 1;
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*{ std::ptr::from_ref(num) }.cast_mut() += 1;
//~^ ERROR casting `&T` to `&mut T` is undefined behavior
*(std::ptr::from_ref({ num }) as *mut i32) += 1;
//~^ ERROR casting `&T` to `&mut T` is undefined behavior

// Shouldn't be warned against
println!("{}", *(num as *const _ as *const i16));
println!("{}", *(mut_num as *mut _ as *mut i16));
ffi(a.as_ptr() as *mut _);
int_ffi(num as *const _ as *mut _);
int_ffi(&3 as *const _ as *mut _);
let mut value = 3;
let value: *const i32 = &mut value;
*(value as *const i16 as *mut i16) = 42;
}
let num = &3i32;

*(a as *const _ as *mut _) = String::from("Replaced");
//~^ ERROR assigning to `&T` is undefined behavior
*(a as *const _ as *mut String) += " world";
//~^ ERROR assigning to `&T` is undefined behavior
*std::ptr::from_ref(num).cast_mut() += 1;
//~^ ERROR assigning to `&T` is undefined behavior
*std::ptr::from_ref({ num }).cast_mut() += 1;
//~^ ERROR assigning to `&T` is undefined behavior
*{ std::ptr::from_ref(num) }.cast_mut() += 1;
//~^ ERROR assigning to `&T` is undefined behavior
*(std::ptr::from_ref({ num }) as *mut i32) += 1;
//~^ ERROR assigning to `&T` is undefined behavior
let value = num as *const i32 as *mut i32;
*value = 1;
//~^ ERROR assigning to `&T` is undefined behavior
}

unsafe fn no_warn() {
let num = &3i32;
let mut_num = &mut 3i32;
let a = &String::from("ffi");

*(num as *const i32 as *mut i32);
println!("{}", *(num as *const _ as *const i16));
println!("{}", *(mut_num as *mut _ as *mut i16));
ffi(a.as_ptr() as *mut _);
int_ffi(num as *const _ as *mut _);
int_ffi(&3 as *const _ as *mut _);
let mut value = 3;
let value: *const i32 = &mut value;
*(value as *const i16 as *mut i16) = 42;
}

fn main() {}
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