From 774e46505453d45732c4ed8c95de1a6c3d3eb6df Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Tue, 16 Apr 2024 14:13:18 +0200 Subject: [PATCH] Box::into_raw: make Miri understand that this is a box-to-raw cast --- .../newtype_pair_retagging.stack.stderr | 2 +- .../newtype_retagging.stack.stderr | 2 +- tests/pass/issues/issue-miri-3473.rs | 28 +++++++++++++++++++ tests/pass/stacked-borrows/stacked-borrows.rs | 12 ++++++++ 4 files changed, 42 insertions(+), 2 deletions(-) create mode 100644 tests/pass/issues/issue-miri-3473.rs diff --git a/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr b/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr index 867907e98e..c26c7f397b 100644 --- a/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr +++ b/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr @@ -6,7 +6,7 @@ LL | Box(unsafe { Unique::new_unchecked(raw) }, alloc) | = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information -help: was created by a Unique retag at offsets [0x0..0x4] +help: was created by a SharedReadWrite retag at offsets [0x0..0x4] --> $DIR/newtype_pair_retagging.rs:LL:CC | LL | let ptr = Box::into_raw(Box::new(0i32)); diff --git a/tests/fail/both_borrows/newtype_retagging.stack.stderr b/tests/fail/both_borrows/newtype_retagging.stack.stderr index 56715938e9..ae54da70fe 100644 --- a/tests/fail/both_borrows/newtype_retagging.stack.stderr +++ b/tests/fail/both_borrows/newtype_retagging.stack.stderr @@ -6,7 +6,7 @@ LL | Box(unsafe { Unique::new_unchecked(raw) }, alloc) | = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information -help: was created by a Unique retag at offsets [0x0..0x4] +help: was created by a SharedReadWrite retag at offsets [0x0..0x4] --> $DIR/newtype_retagging.rs:LL:CC | LL | let ptr = Box::into_raw(Box::new(0i32)); diff --git a/tests/pass/issues/issue-miri-3473.rs b/tests/pass/issues/issue-miri-3473.rs new file mode 100644 index 0000000000..77b960c1cd --- /dev/null +++ b/tests/pass/issues/issue-miri-3473.rs @@ -0,0 +1,28 @@ +//@revisions: stack tree +//@[tree]compile-flags: -Zmiri-tree-borrows +use std::cell::UnsafeCell; + +#[repr(C)] +#[derive(Default)] +struct Node { + _meta: UnsafeCell, + value: usize, +} + +impl Node { + fn value(&self) -> &usize { + &self.value + } +} + +/// This used to cause Stacked Borrows errors because of trouble around conversion +/// from Box to raw pointer. +fn main() { + unsafe { + let a = Box::into_raw(Box::new(Node::default())); + let ptr = &*a; + *UnsafeCell::raw_get(a.cast::>()) = 2; + assert_eq!(*ptr.value(), 0); + drop(Box::from_raw(a)); + } +} diff --git a/tests/pass/stacked-borrows/stacked-borrows.rs b/tests/pass/stacked-borrows/stacked-borrows.rs index 734411ccc7..43ba490d5b 100644 --- a/tests/pass/stacked-borrows/stacked-borrows.rs +++ b/tests/pass/stacked-borrows/stacked-borrows.rs @@ -20,6 +20,7 @@ fn main() { wide_raw_ptr_in_tuple(); not_unpin_not_protected(); write_does_not_invalidate_all_aliases(); + box_into_raw_allows_interior_mutable_alias(); } // Make sure that reading from an `&mut` does, like reborrowing to `&`, @@ -263,3 +264,14 @@ fn write_does_not_invalidate_all_aliases() { other::lib2(); assert_eq!(*x, 1337); // oops, the value changed! I guess not all pointers were invalidated } + +fn box_into_raw_allows_interior_mutable_alias() { unsafe { + let b = Box::new(std::cell::Cell::new(42)); + let raw = Box::into_raw(b); + let c = &*raw; + let d = raw.cast::(); // bypassing `Cell` -- only okay in Miri tests + // `c` and `d` should permit arbitrary aliasing with each other now. + *d = 1; + c.set(2); + drop(Box::from_raw(raw)); +} }