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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UBSan can read past valid memory region"
href="http://llvm.org/bugs/show_bug.cgi?id=20721">20721</a>
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<th>Summary</th>
<td>UBSan can read past valid memory region
</td>
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<th>Product</th>
<td>compiler-rt
</td>
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<th>Version</th>
<td>unspecified
</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>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>compiler-rt
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>y.gribov@samsung.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>It looks like currently when reporting context for memory-related errors, UBSan
may read past the end of valid memory region causing segfaults. The related
code is in renderMemorySnippet (in ubsan_diag.cc):
// Emit data.
for (uptr P = Min; P != Max; ++P) {
// FIXME: Check that the address is readable before printing it.
unsigned char C = *reinterpret_cast<const unsigned char*>(P);
Printf("%s%02x", (P % 8 == 0) ? " " : " ", C);
}
Printf("\n");
Here Max is usually Addr + 28 thus potentially overflowing valid memory range.
Unfortunately I don't have a proper reprocase because the error does not
reproduce on current GCC trunk on x64. But this does appear in GCC autotests
e.g. see <a href="https://gcc.gnu.org/ml/gcc-testresults/2014-08/msg02038.html">https://gcc.gnu.org/ml/gcc-testresults/2014-08/msg02038.html</a> :
FAIL: c-c++-common/ubsan/align-4.c -O2 -flto -fuse-linker-plugin
-fno-fat-lto-objects execution test.</pre>
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</p>
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