diff options
Diffstat (limited to 'compiler/rustc_const_eval/src')
| -rw-r--r-- | compiler/rustc_const_eval/src/lib.rs | 6 | ||||
| -rw-r--r-- | compiler/rustc_const_eval/src/might_permit_raw_init.rs | 44 | ||||
| -rw-r--r-- | compiler/rustc_const_eval/src/util/might_permit_raw_init.rs | 151 | ||||
| -rw-r--r-- | compiler/rustc_const_eval/src/util/mod.rs | 2 |
4 files changed, 155 insertions, 48 deletions
diff --git a/compiler/rustc_const_eval/src/lib.rs b/compiler/rustc_const_eval/src/lib.rs index ebdaf61e439..230f841cf4d 100644 --- a/compiler/rustc_const_eval/src/lib.rs +++ b/compiler/rustc_const_eval/src/lib.rs @@ -32,7 +32,6 @@ extern crate rustc_middle; pub mod const_eval; mod errors; pub mod interpret; -mod might_permit_raw_init; pub mod transform; pub mod util; @@ -61,7 +60,6 @@ pub fn provide(providers: &mut Providers) { const_eval::deref_mir_constant(tcx, param_env, value) }; providers.permits_uninit_init = - |tcx, ty| might_permit_raw_init::might_permit_raw_init(tcx, ty, InitKind::Uninit); - providers.permits_zero_init = - |tcx, ty| might_permit_raw_init::might_permit_raw_init(tcx, ty, InitKind::Zero); + |tcx, ty| util::might_permit_raw_init(tcx, ty, InitKind::UninitMitigated0x01Fill); + providers.permits_zero_init = |tcx, ty| util::might_permit_raw_init(tcx, ty, InitKind::Zero); } diff --git a/compiler/rustc_const_eval/src/might_permit_raw_init.rs b/compiler/rustc_const_eval/src/might_permit_raw_init.rs deleted file mode 100644 index 37ffa19ccd6..00000000000 --- a/compiler/rustc_const_eval/src/might_permit_raw_init.rs +++ /dev/null @@ -1,44 +0,0 @@ -use crate::const_eval::CompileTimeInterpreter; -use crate::interpret::{InterpCx, MemoryKind, OpTy}; -use rustc_middle::ty::layout::LayoutCx; -use rustc_middle::ty::{layout::TyAndLayout, ParamEnv, TyCtxt}; -use rustc_session::Limit; -use rustc_target::abi::InitKind; - -pub fn might_permit_raw_init<'tcx>( - tcx: TyCtxt<'tcx>, - ty: TyAndLayout<'tcx>, - kind: InitKind, -) -> bool { - let strict = tcx.sess.opts.unstable_opts.strict_init_checks; - - if strict { - let machine = CompileTimeInterpreter::new( - Limit::new(0), - /*can_access_statics:*/ false, - /*check_alignment:*/ true, - ); - - let mut cx = InterpCx::new(tcx, rustc_span::DUMMY_SP, ParamEnv::reveal_all(), machine); - - let allocated = cx - .allocate(ty, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap)) - .expect("OOM: failed to allocate for uninit check"); - - if kind == InitKind::Zero { - cx.write_bytes_ptr( - allocated.ptr, - std::iter::repeat(0_u8).take(ty.layout.size().bytes_usize()), - ) - .expect("failed to write bytes for zero valid check"); - } - - let ot: OpTy<'_, _> = allocated.into(); - - // Assume that if it failed, it's a validation failure. - cx.validate_operand(&ot).is_ok() - } else { - let layout_cx = LayoutCx { tcx, param_env: ParamEnv::reveal_all() }; - ty.might_permit_raw_init(&layout_cx, kind) - } -} diff --git a/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs b/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs new file mode 100644 index 00000000000..6ca71223391 --- /dev/null +++ b/compiler/rustc_const_eval/src/util/might_permit_raw_init.rs @@ -0,0 +1,151 @@ +use rustc_middle::ty::layout::{LayoutCx, LayoutOf, TyAndLayout}; +use rustc_middle::ty::{ParamEnv, TyCtxt}; +use rustc_session::Limit; +use rustc_target::abi::{Abi, FieldsShape, InitKind, Scalar, Variants}; + +use crate::const_eval::CompileTimeInterpreter; +use crate::interpret::{InterpCx, MemoryKind, OpTy}; + +/// Determines if this type permits "raw" initialization by just transmuting some memory into an +/// instance of `T`. +/// +/// `init_kind` indicates if the memory is zero-initialized or left uninitialized. We assume +/// uninitialized memory is mitigated by filling it with 0x01, which reduces the chance of causing +/// LLVM UB. +/// +/// By default we check whether that operation would cause *LLVM UB*, i.e., whether the LLVM IR we +/// generate has UB or not. This is a mitigation strategy, which is why we are okay with accepting +/// Rust UB as long as there is no risk of miscompilations. The `strict_init_checks` can be set to +/// do a full check against Rust UB instead (in which case we will also ignore the 0x01-filling and +/// to the full uninit check). +pub fn might_permit_raw_init<'tcx>( + tcx: TyCtxt<'tcx>, + ty: TyAndLayout<'tcx>, + kind: InitKind, +) -> bool { + if tcx.sess.opts.unstable_opts.strict_init_checks { + might_permit_raw_init_strict(ty, tcx, kind) + } else { + let layout_cx = LayoutCx { tcx, param_env: ParamEnv::reveal_all() }; + might_permit_raw_init_lax(ty, &layout_cx, kind) + } +} + +/// Implements the 'strict' version of the `might_permit_raw_init` checks; see that function for +/// details. +fn might_permit_raw_init_strict<'tcx>( + ty: TyAndLayout<'tcx>, + tcx: TyCtxt<'tcx>, + kind: InitKind, +) -> bool { + let machine = CompileTimeInterpreter::new( + Limit::new(0), + /*can_access_statics:*/ false, + /*check_alignment:*/ true, + ); + + let mut cx = InterpCx::new(tcx, rustc_span::DUMMY_SP, ParamEnv::reveal_all(), machine); + + let allocated = cx + .allocate(ty, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap)) + .expect("OOM: failed to allocate for uninit check"); + + if kind == InitKind::Zero { + cx.write_bytes_ptr( + allocated.ptr, + std::iter::repeat(0_u8).take(ty.layout.size().bytes_usize()), + ) + .expect("failed to write bytes for zero valid check"); + } + + let ot: OpTy<'_, _> = allocated.into(); + + // Assume that if it failed, it's a validation failure. + // This does *not* actually check that references are dereferenceable, but since all types that + // require dereferenceability also require non-null, we don't actually get any false negatives + // due to this. + cx.validate_operand(&ot).is_ok() +} + +/// Implements the 'lax' (default) version of the `might_permit_raw_init` checks; see that function for +/// details. +fn might_permit_raw_init_lax<'tcx>( + this: TyAndLayout<'tcx>, + cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, + init_kind: InitKind, +) -> bool { + let scalar_allows_raw_init = move |s: Scalar| -> bool { + match init_kind { + InitKind::Zero => { + // The range must contain 0. + s.valid_range(cx).contains(0) + } + InitKind::UninitMitigated0x01Fill => { + // The range must include an 0x01-filled buffer. + let mut val: u128 = 0x01; + for _ in 1..s.size(cx).bytes() { + // For sizes >1, repeat the 0x01. + val = (val << 8) | 0x01; + } + s.valid_range(cx).contains(val) + } + } + }; + + // Check the ABI. + let valid = match this.abi { + Abi::Uninhabited => false, // definitely UB + Abi::Scalar(s) => scalar_allows_raw_init(s), + Abi::ScalarPair(s1, s2) => scalar_allows_raw_init(s1) && scalar_allows_raw_init(s2), + Abi::Vector { element: s, count } => count == 0 || scalar_allows_raw_init(s), + Abi::Aggregate { .. } => true, // Fields are checked below. + }; + if !valid { + // This is definitely not okay. + return false; + } + + // Special magic check for references and boxes (i.e., special pointer types). + if let Some(pointee) = this.ty.builtin_deref(false) { + let pointee = cx.layout_of(pointee.ty).expect("need to be able to compute layouts"); + // We need to ensure that the LLVM attributes `aligned` and `dereferenceable(size)` are satisfied. + if pointee.align.abi.bytes() > 1 { + // 0x01-filling is not aligned. + return false; + } + if pointee.size.bytes() > 0 { + // A 'fake' integer pointer is not sufficiently dereferenceable. + return false; + } + } + + // If we have not found an error yet, we need to recursively descend into fields. + match &this.fields { + FieldsShape::Primitive | FieldsShape::Union { .. } => {} + FieldsShape::Array { .. } => { + // Arrays never have scalar layout in LLVM, so if the array is not actually + // accessed, there is no LLVM UB -- therefore we can skip this. + } + FieldsShape::Arbitrary { offsets, .. } => { + for idx in 0..offsets.len() { + if !might_permit_raw_init_lax(this.field(cx, idx), cx, init_kind) { + // We found a field that is unhappy with this kind of initialization. + return false; + } + } + } + } + + match &this.variants { + Variants::Single { .. } => { + // All fields of this single variant have already been checked above, there is nothing + // else to do. + } + Variants::Multiple { .. } => { + // We cannot tell LLVM anything about the details of this multi-variant layout, so + // invalid values "hidden" inside the variant cannot cause LLVM trouble. + } + } + + true +} diff --git a/compiler/rustc_const_eval/src/util/mod.rs b/compiler/rustc_const_eval/src/util/mod.rs index a1876bed83e..7a05cfd235f 100644 --- a/compiler/rustc_const_eval/src/util/mod.rs +++ b/compiler/rustc_const_eval/src/util/mod.rs @@ -3,8 +3,10 @@ mod alignment; mod call_kind; pub mod collect_writes; mod find_self_call; +mod might_permit_raw_init; pub use self::aggregate::expand_aggregate; pub use self::alignment::is_disaligned; pub use self::call_kind::{call_kind, CallDesugaringKind, CallKind}; pub use self::find_self_call::find_self_call; +pub use self::might_permit_raw_init::might_permit_raw_init; |