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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [coroutines] Use-after-free by access to coroutine frame after await_suspend()"
href="https://bugs.llvm.org/show_bug.cgi?id=46990">46990</a>
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<th>Summary</th>
<td>[coroutines] Use-after-free by access to coroutine frame after await_suspend()
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C2x
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>alexander.vandergrinten@gmail.com
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Created <span class=""><a href="attachment.cgi?id=23813" name="attach_23813" title="Preprocessed source code">attachment 23813</a> <a href="attachment.cgi?id=23813&action=edit" title="Preprocessed source code">[details]</a></span>
Preprocessed source code
With some optimization options (-O2 and -fsanitize=undefined in this case),
LLVM generates instructions that access coroutine frames after calling
await_suspend() but before returning to the caller/resumer of a coroutine. This
leads to use-after-free if the coroutine is freed before control returns to the
caller. Below is a snippet of LLVM code that demonstrates this; the GEP
instructions cause a bogus access.
The preprocessed source is attached (but unfortunately, I was unable to reduce
the bug to a toy example). Compile with:
clang++ -std=c++20 -O2 -fsanitize=undefined -S -emit-llvm -o out.S out.cpp
This bug happens both with Clang 10.0.1 and 11.0.0-rc1.
Relevant LLVM code:
-------------------
invoke void
@_ZN5async14sender_awaiterIN4thor18CopyFromViewSenderEvE13await_suspendENSt12experimental16coroutine_handleIvEE(%"struct.async::sender_awaiter.44"*
nonnull %31, i8* nonnull %2)
to label %725 unwind label %745
725: ; preds = %723
%726 = getelementptr inbounds
%_ZN4thor15loadModuleImageEN7smarter10shared_ptrINS_12AddressSpaceE14BindableHandleEEmN5frigg9SharedPtrINS_10MemoryViewENS5_13SharedControlEEE.Frame,
%_ZN4thor15loadModuleImageEN7smarter10shared_ptrINS_12AddressSpaceE14BindableHandleEEmN5frigg9SharedPtrINS_10MemoryViewENS5_13SharedControlEEE.Frame*
%0, i64 0, i32 32
%727 = getelementptr inbounds
%_ZN4thor15loadModuleImageEN7smarter10shared_ptrINS_12AddressSpaceE14BindableHandleEEmN5frigg9SharedPtrINS_10MemoryViewENS5_13SharedControlEEE.Frame,
%_ZN4thor15loadModuleImageEN7smarter10shared_ptrINS_12AddressSpaceE14BindableHandleEEmN5frigg9SharedPtrINS_10MemoryViewENS5_13SharedControlEEE.Frame*
%0, i64 0, i32 31
br label %856</pre>
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