From 7867a294cac40da42e50e1f0bb0096300814f234 Mon Sep 17 00:00:00 2001 From: Veera Date: Sun, 22 Sep 2024 19:32:56 -0400 Subject: [PATCH] Add a Lint for Pointer to Integer Transmutes in Consts --- compiler/rustc_lint_defs/src/builtin.rs | 35 +++++++++++++++ compiler/rustc_mir_transform/messages.ftl | 5 +++ compiler/rustc_mir_transform/src/errors.rs | 7 +++ compiler/rustc_mir_transform/src/lib.rs | 2 + library/core/src/ptr/mod.rs | 1 + ...-to-int-transmute-in-consts-issue-87525.rs | 2 +- ...int-transmute-in-consts-issue-87525.stderr | 43 ++++++++++++++++++- 7 files changed, 93 insertions(+), 2 deletions(-) diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs index 25d33126754af..3d7825099d65e 100644 --- a/compiler/rustc_lint_defs/src/builtin.rs +++ b/compiler/rustc_lint_defs/src/builtin.rs @@ -82,6 +82,7 @@ declare_lint_pass! { PRIVATE_INTERFACES, PROC_MACRO_DERIVE_RESOLUTION_FALLBACK, PTR_CAST_ADD_AUTO_TO_OBJECT, + PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE, REDUNDANT_IMPORTS, REDUNDANT_LIFETIMES, @@ -5095,3 +5096,37 @@ declare_lint! { reference: "issue #124535 ", }; } + +declare_lint! { + /// The `ptr_to_integer_transmute_in_consts` lint detects pointer to integer + /// transmute in const functions and associated constants. + /// + /// ### Example + /// + /// ```rust,compile_fail + /// const fn foo(ptr: *const u8) -> usize { + /// unsafe { + /// std::mem::transmute::<*const u8, usize>(ptr) + /// } + /// } + /// ``` + /// + /// {{produces}} + /// + /// ### Explanation + /// + /// Transmuting pointers to integers in a `const` context is undefined behavior. + /// Any attempt to use the resulting integer will abort const-evaluation. + /// + /// But sometimes the compiler might not emit an error for pointer to integer transmutes + /// inside const functions and associated consts because they are evaluated only when referenced. + /// Therefore, this lint serves as an extra layer of defense to prevent any undefined behavior + /// from compiling without any warnings or errors. + /// + /// See [std::mem::transmute] in the reference for more details. + /// + /// [std::mem::transmute]: https://doc.rust-lang.org/std/mem/fn.transmute.html + pub PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS, + Deny, + "detects attempts to transmute a pointer to integer in const context", +} diff --git a/compiler/rustc_mir_transform/messages.ftl b/compiler/rustc_mir_transform/messages.ftl index f9b79d72b0504..b81c090673476 100644 --- a/compiler/rustc_mir_transform/messages.ftl +++ b/compiler/rustc_mir_transform/messages.ftl @@ -27,3 +27,8 @@ mir_transform_unaligned_packed_ref = reference to packed field is unaligned .note = packed structs are only aligned by one byte, and many modern architectures penalize unaligned field accesses .note_ub = creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) .help = copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers) + +mir_transform_undefined_transmute = pointers cannot be transmuted to integers during const eval + .note = at compile-time, pointers do not have an integer value + .note2 = avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior + .help = for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs index 9a93c3a72b1c9..e480537402da1 100644 --- a/compiler/rustc_mir_transform/src/errors.rs +++ b/compiler/rustc_mir_transform/src/errors.rs @@ -121,3 +121,10 @@ pub(crate) struct MustNotSuspendReason { pub span: Span, pub reason: String, } + +#[derive(LintDiagnostic)] +#[diag(mir_transform_undefined_transmute)] +#[note] +#[note(mir_transform_note2)] +#[help] +pub(crate) struct UndefinedTransmute; diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs index 84d07d3833071..626b4584fb27f 100644 --- a/compiler/rustc_mir_transform/src/lib.rs +++ b/compiler/rustc_mir_transform/src/lib.rs @@ -51,6 +51,7 @@ mod add_subtyping_projections; mod check_alignment; mod check_const_item_mutation; mod check_packed_ref; +mod check_undefined_transmutes; // This pass is public to allow external drivers to perform MIR cleanup pub mod cleanup_post_borrowck; mod copy_prop; @@ -293,6 +294,7 @@ fn mir_built(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal> { &Lint(check_packed_ref::CheckPackedRef), &Lint(check_const_item_mutation::CheckConstItemMutation), &Lint(function_item_references::FunctionItemReferences), + &Lint(check_undefined_transmutes::CheckUndefinedTransmutes), // What we need to do constant evaluation. &simplify::SimplifyCfg::Initial, &Lint(sanity_check::SanityCheck), diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs index 08d06cad55d06..8d6560111dad0 100644 --- a/library/core/src/ptr/mod.rs +++ b/library/core/src/ptr/mod.rs @@ -1916,6 +1916,7 @@ pub unsafe fn write_volatile(dst: *mut T, src: T) { /// than trying to adapt this to accommodate that change. /// /// Any questions go to @nagisa. +#[cfg_attr(not(bootstrap), allow(ptr_to_integer_transmute_in_consts))] #[lang = "align_offset"] pub(crate) const unsafe fn align_offset(p: *const T, a: usize) -> usize { // FIXME(#75598): Direct use of these intrinsics improves codegen significantly at opt-level <= diff --git a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs index f8e97904e9e08..e675ca59f425c 100644 --- a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs +++ b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs @@ -62,7 +62,7 @@ const fn zoom(ptr: *const u8) -> usize { //~^ ERROR pointers cannot be transmuted to integers } } - + fn main() { const a: u8 = 10; const value: usize = zoom(&a); diff --git a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr index a57bc8e1e70ec..685b56bf9b259 100644 --- a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr +++ b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr @@ -1,3 +1,14 @@ +error: pointers cannot be transmuted to integers during const eval + --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:61:9 + | +LL | std::mem::transmute(ptr) + | ^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: at compile-time, pointers do not have an integer value + = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior + = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html + = note: `#[deny(ptr_to_integer_transmute_in_consts)]` on by default + error[E0080]: evaluation of constant value failed --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:68:26 | @@ -7,6 +18,36 @@ LL | const value: usize = zoom(&a); = help: this code performed an operation that depends on the underlying bytes representing a pointer = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported -error: aborting due to 1 previous error +error: pointers cannot be transmuted to integers during const eval + --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:3:9 + | +LL | std::mem::transmute(ptr) + | ^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: at compile-time, pointers do not have an integer value + = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior + = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html + +error: pointers cannot be transmuted to integers during const eval + --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:13:13 + | +LL | std::mem::transmute(ptr) + | ^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: at compile-time, pointers do not have an integer value + = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior + = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html + +error: pointers cannot be transmuted to integers during const eval + --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:30:13 + | +LL | std::mem::transmute(ptr) + | ^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: at compile-time, pointers do not have an integer value + = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior + = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html + +error: aborting due to 5 previous errors For more information about this error, try `rustc --explain E0080`.