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Stacked Borrows: factor the logic determining the new permissions on retag into a separate function

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This commit is contained in:
Ralf Jung 2022-12-05 18:19:18 +01:00
parent 9397ea1368
commit 34c58e897f
3 changed files with 187 additions and 167 deletions
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4
src/tools/miri/src/borrow_tracker/stacked_borrows/diagnostics.rs
View File

@ -459,10 +459,10 @@ impl<'history, 'ecx, 'mir, 'tcx> DiagnosticCx<'history, 'ecx, 'mir, 'tcx> {
Operation::Dealloc(_) => format!(" due to deallocation"),
Operation::Access(AccessOp { kind, tag, .. }) =>
format!(" due to {kind:?} access for {tag:?}"),
Operation::Retag(RetagOp { orig_tag, permission, .. }) => {
Operation::Retag(RetagOp { orig_tag, permission, new_tag, .. }) => {
let permission = permission
.expect("start_grant should set the current permission before popping a tag");
format!(" due to {permission:?} retag from {orig_tag:?}")
format!(" due to {permission:?} retag from {orig_tag:?} (that retag created {new_tag:?})")
}
};

340
src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs
View File

@ -1,13 +1,13 @@
//! Implements "Stacked Borrows". See <https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md>
//! for further information.
pub mod diagnostics;
mod item;
mod stack;
pub mod diagnostics;
use log::trace;
use std::cmp;
use std::fmt::{self, Write};
use std::fmt::Write;
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::mir::{Mutability, RetagKind};
@ -23,9 +23,9 @@ use crate::borrow_tracker::{
};
use crate::*;
use diagnostics::RetagCause;
pub use item::{Item, Permission};
pub use stack::Stack;
use diagnostics::RetagCause;
pub type AllocState = Stacks;
@ -42,30 +42,104 @@ pub struct Stacks {
modified_since_last_gc: bool,
}
/// Indicates which kind of reference is being created.
/// Used by high-level `reborrow` to compute which permissions to grant to the
/// new pointer.
#[derive(Copy, Clone, Hash, PartialEq, Eq)]
enum RefKind {
/// `Box`.
Box,
/// `&mut`.
Unique { two_phase: bool },
/// `&` with or without interior mutability.
Shared,
/// `*mut`/`*const` (raw pointers).
Raw { mutable: bool },
/// Indicates which permissions to grant to the retagged pointer.
#[derive(Clone, Debug)]
enum NewPermission {
Uniform {
perm: Permission,
access: Option<AccessKind>,
protector: Option<ProtectorKind>,
},
FreezeSensitive {
freeze_perm: Permission,
freeze_access: Option<AccessKind>,
freeze_protector: Option<ProtectorKind>,
nonfreeze_perm: Permission,
nonfreeze_access: Option<AccessKind>,
// nonfreeze_protector must always be None
},
}
impl fmt::Display for RefKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
impl NewPermission {
/// A key function: determine the permissions to grant at a retag for the given kind of
/// reference/pointer.
fn from_ref_ty<'tcx>(
ty: ty::Ty<'tcx>,
kind: RetagKind,
cx: &crate::MiriInterpCx<'_, 'tcx>,
) -> Self {
let protector = (kind == RetagKind::FnEntry).then_some(ProtectorKind::StrongProtector);
match ty.kind() {
ty::Ref(_, pointee, Mutability::Mut) => {
if kind == RetagKind::TwoPhase {
// We mostly just give up on 2phase-borrows, and treat these exactly like raw pointers.
assert!(protector.is_none()); // RetagKind can't be both FnEntry and TwoPhase.
NewPermission::Uniform {
perm: Permission::SharedReadWrite,
access: None,
protector: None,
}
} else if pointee.is_unpin(*cx.tcx, cx.param_env()) {
// A regular full mutable reference.
NewPermission::Uniform {
perm: Permission::Unique,
access: Some(AccessKind::Write),
protector,
}
} else {
NewPermission::Uniform {
perm: Permission::SharedReadWrite,
// FIXME: We emit `dereferenceable` for `!Unpin` mutable references, so we
// should do fake accesses here. But then we run into
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/381>, so for now
// we don't do that.
access: None,
protector,
}
}
}
ty::RawPtr(ty::TypeAndMut { mutbl: Mutability::Mut, .. }) => {
assert!(protector.is_none()); // RetagKind can't be both FnEntry and Raw.
// Mutable raw pointer. No access, not protected.
NewPermission::Uniform {
perm: Permission::SharedReadWrite,
access: None,
protector: None,
}
}
ty::Ref(_, _pointee, Mutability::Not) => {
NewPermission::FreezeSensitive {
freeze_perm: Permission::SharedReadOnly,
freeze_access: Some(AccessKind::Read),
freeze_protector: protector,
nonfreeze_perm: Permission::SharedReadWrite,
// Inside UnsafeCell, this does *not* count as an access, as there
// might actually be mutable references further up the stack that
// we have to keep alive.
nonfreeze_access: None,
// We do not protect inside UnsafeCell.
// This fixes https://github.com/rust-lang/rust/issues/55005.
}
}
ty::RawPtr(ty::TypeAndMut { mutbl: Mutability::Not, .. }) => {
assert!(protector.is_none()); // RetagKind can't be both FnEntry and Raw.
// `*const T`, when freshly created, are read-only in the frozen part.
NewPermission::FreezeSensitive {
freeze_perm: Permission::SharedReadOnly,
freeze_access: Some(AccessKind::Read),
freeze_protector: None,
nonfreeze_perm: Permission::SharedReadWrite,
nonfreeze_access: None,
}
}
_ => unreachable!(),
}
}
fn protector(&self) -> Option<ProtectorKind> {
match self {
RefKind::Box => write!(f, "Box"),
RefKind::Unique { two_phase: false } => write!(f, "unique reference"),
RefKind::Unique { two_phase: true } => write!(f, "unique reference (two-phase)"),
RefKind::Shared => write!(f, "shared reference"),
RefKind::Raw { mutable: true } => write!(f, "raw (mutable) pointer"),
RefKind::Raw { mutable: false } => write!(f, "raw (constant) pointer"),
NewPermission::Uniform { protector, .. } => *protector,
NewPermission::FreezeSensitive { freeze_protector, .. } => *freeze_protector,
}
}
}
@ -520,10 +594,9 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
&mut self,
place: &MPlaceTy<'tcx, Provenance>,
size: Size,
kind: RefKind,
retag_cause: RetagCause, // What caused this retag, for diagnostics only
new_perm: NewPermission,
new_tag: BorTag,
protect: Option<ProtectorKind>,
retag_cause: RetagCause, // What caused this retag, for diagnostics only
) -> InterpResult<'tcx, Option<AllocId>> {
let this = self.eval_context_mut();
@ -534,20 +607,16 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
let global = this.machine.borrow_tracker.as_ref().unwrap().borrow();
let ty = place.layout.ty;
if global.tracked_pointer_tags.contains(&new_tag) {
let mut kind_str = format!("{kind}");
match kind {
RefKind::Unique { two_phase: false }
if !ty.is_unpin(*this.tcx, this.param_env()) =>
{
write!(kind_str, " (!Unpin pointee type {ty})").unwrap()
},
RefKind::Shared
if !ty.is_freeze(*this.tcx, this.param_env()) =>
{
write!(kind_str, " (!Freeze pointee type {ty})").unwrap()
},
_ => write!(kind_str, " (pointee type {ty})").unwrap(),
};
let mut kind_str = String::new();
match new_perm {
NewPermission::Uniform { perm, .. } =>
write!(kind_str, "{perm:?} permission").unwrap(),
NewPermission::FreezeSensitive { freeze_perm, .. } if ty.is_freeze(*this.tcx, this.param_env()) =>
write!(kind_str, "{freeze_perm:?} permission").unwrap(),
NewPermission::FreezeSensitive { freeze_perm, nonfreeze_perm, .. } =>
write!(kind_str, "{freeze_perm:?}/{nonfreeze_perm:?} permission for frozen/non-frozen parts").unwrap(),
}
write!(kind_str, " (pointee type {ty})").unwrap();
this.emit_diagnostic(NonHaltingDiagnostic::CreatedPointerTag(
new_tag.inner(),
Some(kind_str),
@ -581,7 +650,7 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
);
let mut dcx = dcx.build(&mut stacked_borrows.history, base_offset);
dcx.log_creation();
if protect.is_some() {
if new_perm.protector().is_some() {
dcx.log_protector();
}
},
@ -594,8 +663,7 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
if size == Size::ZERO {
trace!(
"reborrow of size 0: {} reference {:?} derived from {:?} (pointee {})",
kind,
"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
new_tag,
place.ptr,
place.layout.ty,
@ -632,8 +700,7 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
}
trace!(
"reborrow: {} reference {:?} derived from {:?} (pointee {}): {:?}, size {}",
kind,
"reborrow: reference {:?} derived from {:?} (pointee {}): {:?}, size {}",
new_tag,
orig_tag,
place.layout.ty,
@ -641,7 +708,7 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
size.bytes()
);
if let Some(protect) = protect {
if let Some(protect) = new_perm.protector() {
// See comment in `Stack::item_invalidated` for why we store the tag twice.
this.frame_mut().extra.borrow_tracker.as_mut().unwrap().protected_tags.push(new_tag);
this.machine
@ -653,30 +720,45 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
.insert(new_tag, protect);
}
// Update the stacks.
// Make sure that raw pointers and mutable shared references are reborrowed "weak":
// There could be existing unique pointers reborrowed from them that should remain valid!
let (perm, access) = match kind {
RefKind::Unique { two_phase } => {
// Permission is Unique only if the type is `Unpin` and this is not twophase
if !two_phase && place.layout.ty.is_unpin(*this.tcx, this.param_env()) {
(Permission::Unique, Some(AccessKind::Write))
} else {
// FIXME: We emit `dereferenceable` for `!Unpin` mutable references, so we
// should do fake accesses here. But then we run into
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/381>, so for now
// we don't do that.
(Permission::SharedReadWrite, None)
// Update the stacks, according to the new permission information we are given.
match new_perm {
NewPermission::Uniform { perm, access, protector } => {
assert!(perm != Permission::SharedReadOnly);
// Here we can avoid `borrow()` calls because we have mutable references.
// Note that this asserts that the allocation is mutable -- but since we are creating a
// mutable pointer, that seems reasonable.
let (alloc_extra, machine) = this.get_alloc_extra_mut(alloc_id)?;
let stacked_borrows = alloc_extra.borrow_tracker_sb_mut().get_mut();
let item = Item::new(new_tag, perm, protector.is_some());
let range = alloc_range(base_offset, size);
let global = machine.borrow_tracker.as_ref().unwrap().borrow();
let dcx = DiagnosticCxBuilder::retag(
machine,
retag_cause,
new_tag,
orig_tag,
alloc_range(base_offset, size),
);
stacked_borrows.for_each(range, dcx, |stack, dcx, exposed_tags| {
stack.grant(orig_tag, item, access, &global, dcx, exposed_tags)
})?;
drop(global);
if let Some(access) = access {
assert_eq!(access, AccessKind::Write);
// Make sure the data race model also knows about this.
if let Some(data_race) = alloc_extra.data_race.as_mut() {
data_race.write(alloc_id, range, machine)?;
}
}
}
RefKind::Box => (Permission::Unique, Some(AccessKind::Write)),
RefKind::Raw { mutable: true } => {
// Creating a raw ptr does not count as an access
(Permission::SharedReadWrite, None)
}
RefKind::Shared | RefKind::Raw { mutable: false } => {
// Shared references and *const are a whole different kind of game, the
// permission is not uniform across the entire range!
NewPermission::FreezeSensitive {
freeze_perm,
freeze_access,
freeze_protector,
nonfreeze_perm,
nonfreeze_access,
} => {
// The permission is not uniform across the entire range!
// We need a frozen-sensitive reborrow.
// We have to use shared references to alloc/memory_extra here since
// `visit_freeze_sensitive` needs to access the global state.
@ -686,22 +768,12 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
// Adjust range.
range.start += base_offset;
// We are only ever `SharedReadOnly` inside the frozen bits.
let (perm, access) = if frozen {
(Permission::SharedReadOnly, Some(AccessKind::Read))
let (perm, access, protector) = if frozen {
(freeze_perm, freeze_access, freeze_protector)
} else {
// Inside UnsafeCell, this does *not* count as an access, as there
// might actually be mutable references further up the stack that
// we have to keep alive.
(Permission::SharedReadWrite, None)
(nonfreeze_perm, nonfreeze_access, None)
};
let protected = if frozen {
protect.is_some()
} else {
// We do not protect inside UnsafeCell.
// This fixes https://github.com/rust-lang/rust/issues/55005.
false
};
let item = Item::new(new_tag, perm, protected);
let item = Item::new(new_tag, perm, protector.is_some());
let global = this.machine.borrow_tracker.as_ref().unwrap().borrow();
let dcx = DiagnosticCxBuilder::retag(
&this.machine,
@ -723,34 +795,6 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
}
Ok(())
})?;
return Ok(Some(alloc_id));
}
};
// Here we can avoid `borrow()` calls because we have mutable references.
// Note that this asserts that the allocation is mutable -- but since we are creating a
// mutable pointer, that seems reasonable.
let (alloc_extra, machine) = this.get_alloc_extra_mut(alloc_id)?;
let stacked_borrows = alloc_extra.borrow_tracker_sb_mut().get_mut();
let item = Item::new(new_tag, perm, protect.is_some());
let range = alloc_range(base_offset, size);
let global = machine.borrow_tracker.as_ref().unwrap().borrow();
let dcx = DiagnosticCxBuilder::retag(
machine,
retag_cause,
new_tag,
orig_tag,
alloc_range(base_offset, size),
);
stacked_borrows.for_each(range, dcx, |stack, dcx, exposed_tags| {
stack.grant(orig_tag, item, access, &global, dcx, exposed_tags)
})?;
drop(global);
if let Some(access) = access {
assert_eq!(access, AccessKind::Write);
// Make sure the data race model also knows about this.
if let Some(data_race) = alloc_extra.data_race.as_mut() {
data_race.write(alloc_id, range, machine)?;
}
}
@ -762,9 +806,8 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
fn sb_retag_reference(
&mut self,
val: &ImmTy<'tcx, Provenance>,
kind: RefKind,
retag_cause: RetagCause, // What caused this retag, for diagnostics only
protect: Option<ProtectorKind>,
new_perm: NewPermission,
cause: RetagCause, // What caused this retag, for diagnostics only
) -> InterpResult<'tcx, ImmTy<'tcx, Provenance>> {
let this = self.eval_context_mut();
// We want a place for where the ptr *points to*, so we get one.
@ -782,7 +825,7 @@ trait EvalContextPrivExt<'mir: 'ecx, 'tcx: 'mir, 'ecx>: crate::MiriInterpCxExt<'
let new_tag = this.machine.borrow_tracker.as_mut().unwrap().get_mut().new_ptr();
// Reborrow.
let alloc_id = this.sb_reborrow(&place, size, kind, retag_cause, new_tag, protect)?;
let alloc_id = this.sb_reborrow(&place, size, new_perm, new_tag, cause)?;
// Adjust pointer.
let new_place = place.map_provenance(|p| {
@ -815,25 +858,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
val: &ImmTy<'tcx, Provenance>,
) -> InterpResult<'tcx, ImmTy<'tcx, Provenance>> {
let this = self.eval_context_mut();
let ref_kind = match val.layout.ty.kind() {
ty::Ref(_, _, mutbl) => {
match mutbl {
Mutability::Mut =>
RefKind::Unique { two_phase: kind == RetagKind::TwoPhase },
Mutability::Not => RefKind::Shared,
}
}
ty::RawPtr(tym) => {
RefKind::Raw { mutable: tym.mutbl == Mutability::Mut }
}
_ => unreachable!(),
};
let new_perm = NewPermission::from_ref_ty(val.layout.ty, kind, this);
let retag_cause = match kind {
RetagKind::TwoPhase { .. } => RetagCause::TwoPhase,
RetagKind::FnEntry => unreachable!(),
RetagKind::Raw | RetagKind::Default => RetagCause::Normal,
};
this.sb_retag_reference(&val, ref_kind, retag_cause, None)
this.sb_retag_reference(&val, new_perm, retag_cause)
}
fn sb_retag_place_contents(
@ -844,7 +875,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
let this = self.eval_context_mut();
let retag_fields = this.machine.borrow_tracker.as_mut().unwrap().get_mut().retag_fields;
let retag_cause = match kind {
RetagKind::Raw | RetagKind::TwoPhase { .. } => unreachable!(),
RetagKind::Raw | RetagKind::TwoPhase { .. } => unreachable!(), // these can only happen in `retag_ptr_value`
RetagKind::FnEntry => RetagCause::FnEntry,
RetagKind::Default => RetagCause::Normal,
};
@ -863,12 +894,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
fn retag_ptr_inplace(
&mut self,
place: &PlaceTy<'tcx, Provenance>,
ref_kind: RefKind,
new_perm: NewPermission,
retag_cause: RetagCause,
protector: Option<ProtectorKind>,
) -> InterpResult<'tcx> {
let val = self.ecx.read_immediate(&self.ecx.place_to_op(place)?)?;
let val = self.ecx.sb_retag_reference(&val, ref_kind, retag_cause, protector)?;
let val = self.ecx.sb_retag_reference(&val, new_perm, retag_cause)?;
self.ecx.write_immediate(*val, place)?;
Ok(())
}
@ -885,13 +915,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
fn visit_box(&mut self, place: &PlaceTy<'tcx, Provenance>) -> InterpResult<'tcx> {
// Boxes get a weak protectors, since they may be deallocated.
self.retag_ptr_inplace(
place,
RefKind::Box,
self.retag_cause,
/*protector*/
(self.kind == RetagKind::FnEntry).then_some(ProtectorKind::WeakProtector),
)
let new_perm = NewPermission::Uniform {
perm: Permission::Unique,
access: Some(AccessKind::Write),
protector: (self.kind == RetagKind::FnEntry)
.then_some(ProtectorKind::WeakProtector),
};
self.retag_ptr_inplace(place, new_perm, self.retag_cause)
}
fn visit_value(&mut self, place: &PlaceTy<'tcx, Provenance>) -> InterpResult<'tcx> {
@ -905,20 +935,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
// Check the type of this value to see what to do with it (retag, or recurse).
match place.layout.ty.kind() {
ty::Ref(_, _, mutbl) => {
let ref_kind = match mutbl {
Mutability::Mut =>
RefKind::Unique { two_phase: false },
Mutability::Not => RefKind::Shared,
};
self.retag_ptr_inplace(
place,
ref_kind,
self.retag_cause,
/*protector*/
(self.kind == RetagKind::FnEntry)
.then_some(ProtectorKind::StrongProtector),
)?;
ty::Ref(..) => {
let new_perm =
NewPermission::from_ref_ty(place.layout.ty, self.kind, self.ecx);
self.retag_ptr_inplace(place, new_perm, self.retag_cause)?;
}
ty::RawPtr(..) => {
// We do *not* want to recurse into raw pointers -- wide raw pointers have
@ -972,12 +992,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
let ptr_layout = this.layout_of(this.tcx.mk_mut_ptr(return_place.layout.ty))?;
let val = ImmTy::from_immediate(return_place.to_ref(this), ptr_layout);
// Reborrow it. With protection! That is part of the point.
let val = this.sb_retag_reference(
&val,
RefKind::Unique { two_phase: false },
RetagCause::FnReturn,
/*protector*/ Some(ProtectorKind::StrongProtector),
)?;
let new_perm = NewPermission::Uniform {
perm: Permission::Unique,
access: Some(AccessKind::Write),
protector: Some(ProtectorKind::StrongProtector),
};
let val = this.sb_retag_reference(&val, new_perm, RetagCause::FnReturn)?;
// And use reborrowed pointer for return place.
let return_place = this.ref_to_mplace(&val)?;
this.frame_mut().return_place = return_place.into();

10
src/tools/miri/src/diagnostics.rs
View File

@ -63,9 +63,9 @@ impl MachineStopType for TerminationInfo {}
/// Miri specific diagnostics
pub enum NonHaltingDiagnostic {
/// (new_tag, new_kind, (alloc_id, base_offset, orig_tag))
/// (new_tag, new_perm, (alloc_id, base_offset, orig_tag))
///
/// new_kind is `None` for base tags.
/// new_perm is `None` for base tags.
CreatedPointerTag(NonZeroU64, Option<String>, Option<(AllocId, AllocRange, ProvenanceExtra)>),
/// This `Item` was popped from the borrow stack. The string explains the reason.
PoppedPointerTag(Item, String),
@ -393,10 +393,10 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
let msg = match &e {
CreatedPointerTag(tag, None, _) => format!("created base tag {tag:?}"),
CreatedPointerTag(tag, Some(kind), None) => format!("created {tag:?} for {kind}"),
CreatedPointerTag(tag, Some(kind), Some((alloc_id, range, orig_tag))) =>
CreatedPointerTag(tag, Some(perm), None) => format!("created {tag:?} with {perm} derived from unknown tag"),
CreatedPointerTag(tag, Some(perm), Some((alloc_id, range, orig_tag))) =>
format!(
"created tag {tag:?} for {kind} at {alloc_id:?}{range:?} derived from {orig_tag:?}"
"created tag {tag:?} with {perm} at {alloc_id:?}{range:?} derived from {orig_tag:?}"
),
PoppedPointerTag(item, cause) => format!("popped tracked tag for item {item:?}{cause}"),
CreatedCallId(id) => format!("function call with id {id}"),