fix vec::IntoIter::drop on high-alignment ZST #106084
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The Miri subtree was changed cc @rust-lang/miri Hey! It looks like you've submitted a new PR for the library teams! If this PR contains changes to any Examples of
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RalfJung
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Dec 23, 2022
| self.ptr = self.end; | ||
| // For th ZST case, it is crucial that we mutate `end` here, not `ptr`. | ||
| // `ptr` must stay aligned, while `end` may be unaligned. | ||
| self.end = self.ptr; |
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FWIW I don't think we have a test for this (with a ZST that needs alignment)
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Wouldn't it be better to add the tests to std instead of the miri testsuite then?
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I'm not sure how this test would be written in std in a way that would actually test the behavior except under miri.
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Maybe by adding an unsafe precondition debug assert to drop_in_place?
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I would not be opposed to that, but I don't think it needs to be done in this PR.
RalfJung
commented
Dec 23, 2022
| // which is valid for ZSTs. | ||
| self.ptr = self.ptr.wrapping_byte_add(step_size); | ||
| // See `next` for why we sub `end` here. | ||
| self.end = self.end.wrapping_byte_sub(step_size); |
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FWIW I don't think we have a test for this (with a ZST that needs alignment)
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Subtle, nice catch. @bors r+ rollup |
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matthiaskrgr
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Dec 23, 2022
fix vec::IntoIter::drop on high-alignment ZST This fixes a soundness bug: IntoIter would call `drop_in_place` on an insufficiently aligned pointer. So if a ZST with alignment greater 1 had drop glue, that would be called with an unaligned reference. Since rust-lang#103957, Miri checks alignment even if the type does not have drop glue, which is how this bug was found. r? `@thomcc`
This was referenced Dec 23, 2022
bors
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Dec 24, 2022
…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#105970 (docs/test: add UI test and long-form error docs for E0462) - rust-lang#105975 (rustc: Remove needless lifetimes) - rust-lang#106069 (rustdoc: use a more evocative name for CSS/JS `#titles`) - rust-lang#106084 (fix vec::IntoIter::drop on high-alignment ZST) - rust-lang#106091 (Use correct CSS pseudo-element selector) - rust-lang#106093 (rustdoc: remove no-op CSS from `.docblock-short`) - rust-lang#106102 (Fix `triagebot.toml`) Failed merges: - rust-lang#106028 (docs/test: add UI test and long-form error docs for `E0461`) r? `@ghost` `@rustbot` modify labels: rollup
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There is a way to write a test without Miri: define a ZST with high alignment and give it an impl Drop that checks alignment.
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bors
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Dec 25, 2022
add lib tests for vec::IntoIter alignment issues This adds non-Miri tests for the issue fixed in rust-lang#106084 r? `@thomcc`
Aaron1011
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Jan 6, 2023
fix vec::IntoIter::drop on high-alignment ZST This fixes a soundness bug: IntoIter would call `drop_in_place` on an insufficiently aligned pointer. So if a ZST with alignment greater 1 had drop glue, that would be called with an unaligned reference. Since rust-lang#103957, Miri checks alignment even if the type does not have drop glue, which is how this bug was found. r? ``@thomcc``
Aaron1011
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Jan 6, 2023
…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#105970 (docs/test: add UI test and long-form error docs for E0462) - rust-lang#105975 (rustc: Remove needless lifetimes) - rust-lang#106069 (rustdoc: use a more evocative name for CSS/JS `#titles`) - rust-lang#106084 (fix vec::IntoIter::drop on high-alignment ZST) - rust-lang#106091 (Use correct CSS pseudo-element selector) - rust-lang#106093 (rustdoc: remove no-op CSS from `.docblock-short`) - rust-lang#106102 (Fix `triagebot.toml`) Failed merges: - rust-lang#106028 (docs/test: add UI test and long-form error docs for `E0461`) r? `@ghost` `@rustbot` modify labels: rollup
thomcc
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May 31, 2023
add lib tests for vec::IntoIter alignment issues This adds non-Miri tests for the issue fixed in rust-lang/rust#106084 r? `@thomcc`
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This fixes a soundness bug: IntoIter would call
drop_in_placeon an insufficiently aligned pointer. So if a ZST with alignment greater 1 had drop glue, that would be called with an unaligned reference. Since #103957, Miri checks alignment even if the type does not have drop glue, which is how this bug was found.r? @thomcc