new restriction lint: division_remainder_used

clippy_lints/src/declared_lints.rs

@@ -236,6 +236,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::instant_subtraction::MANUAL_INSTANT_ELAPSED_INFO,
     crate::instant_subtraction::UNCHECKED_DURATION_SUBTRACTION_INFO,
     crate::int_plus_one::INT_PLUS_ONE_INFO,
+    crate::integer_division_remainder_used::INTEGER_DIVISION_REMAINDER_USED_INFO,
     crate::invalid_upcast_comparisons::INVALID_UPCAST_COMPARISONS_INFO,
     crate::item_name_repetitions::ENUM_VARIANT_NAMES_INFO,
     crate::item_name_repetitions::MODULE_INCEPTION_INFO,

clippy_lints/src/integer_division_remainder_used.rs

@@ -0,0 +1,50 @@
+use clippy_utils::diagnostics::span_lint;
+use rustc_ast::BinOpKind;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::{self};
+use rustc_session::declare_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for the usage of division (/) and remainder (%) operations
+    /// when performed on any integer types using the default Div and Rem trait implementations.
+    ///
+    /// ### Why is this bad?
+    /// In cryptographic contexts, division can result in timing sidechannel vulnerabilities,
+    /// and needs to be replaced with constant-time code instead (e.g. Barrett reduction).
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let my_div = 10 / 2;
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let my_div = 10 >> 1;
+    /// ```
+    #[clippy::version = "1.78.0"]
+    pub INTEGER_DIVISION_REMAINDER_USED,
+    restriction,
+    "use of disallowed default division and remainder operations"
+}
+
+declare_lint_pass!(IntegerDivisionRemainderUsed => [INTEGER_DIVISION_REMAINDER_USED]);
+
+impl LateLintPass<'_> for IntegerDivisionRemainderUsed {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+        if let ExprKind::Binary(op, lhs, rhs) = &expr.kind
+            && let BinOpKind::Div | BinOpKind::Rem = op.node
+            && let lhs_ty = cx.typeck_results().expr_ty(lhs)
+            && let rhs_ty = cx.typeck_results().expr_ty(rhs)
+            && let ty::Int(_) | ty::Uint(_) = lhs_ty.peel_refs().kind()
+            && let ty::Int(_) | ty::Uint(_) = rhs_ty.peel_refs().kind()
+        {
+            span_lint(
+                cx,
+                INTEGER_DIVISION_REMAINDER_USED,
+                expr.span.source_callsite(),
+                &format!("use of {} has been disallowed in this context", op.node.as_str()),
+            );
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -172,6 +172,7 @@ mod init_numbered_fields;
 mod inline_fn_without_body;
 mod instant_subtraction;
 mod int_plus_one;
+mod integer_division_remainder_used;
 mod invalid_upcast_comparisons;
 mod item_name_repetitions;
 mod items_after_statements;
@@ -1124,6 +1125,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(assigning_clones::AssigningClones));
     store.register_late_pass(|_| Box::new(zero_repeat_side_effects::ZeroRepeatSideEffects));
     store.register_late_pass(|_| Box::new(manual_unwrap_or_default::ManualUnwrapOrDefault));
+    store.register_late_pass(|_| Box::new(integer_division_remainder_used::IntegerDivisionRemainderUsed));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }