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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">There's a patch on Phabricator to implement a detector pass, in a more static-analysis mode; it seems to be doing better than the Microsoft option but still
isn't catching everything.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><a href="https://reviews.llvm.org/D43643">https://reviews.llvm.org/D43643</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-dev [mailto:cfe-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>Dallman, John via cfe-dev<br>
<b>Sent:</b> Wednesday, March 21, 2018 5:59 AM<br>
<b>To:</b> 'cfe-dev@lists.llvm.org'<br>
<b>Subject:</b> [cfe-dev] Clang insertion of fence instructions to mitigate Spectre variant 1?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">As far as I've been able to learn, the only way to avoid security vulnerabilities due to Spectre variant 1 (</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">CVE-2017-5753,
“bounds check bypass”) is to insert fences to control the relevant speculative reads. I'm interested in doing this because I work on a numerical modelling library that is used in many applications, which are used to handle valuable information. There's been
at least one piece of malware that specifically targeted one of those applications, so I work at a moderate level of paranoia.
</span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">I've found information about __builtin_load_no_speculate, but inserting those by hand into ten million lines of branchy C code that's under active development is not an attractive
prospect.</span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> </span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">MSVC has recently gained a /QSpectre option that tries to do this for you (<a href="https://blogs.msdn.microsoft.com/vcblog/2018/01/15/spectre-mitigations-in-msvc/"><span style="color:#0563C1">https://blogs.msdn.microsoft.com/vcblog/2018/01/15/spectre-mitigations-in-msvc/</span></a>).
It only handles a very limited range of cases at present (<a href="https://www.paulkocher.com/doc/MicrosoftCompilerSpectreMitigation.html"><span style="color:#0563C1">https://www.paulkocher.com/doc/MicrosoftCompilerSpectreMitigation.html</span></a>), but Microsoft
are working on improving that. Red Hat tell me that there is work underway to add something similar to GCC, although it's probably a year away.
</span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> </span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">While such a capability can't be completely fool-proof, I can well believe that it's possible to do as good a job as bored humans, and it will be much cheaper.
</span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Are there any plans to add something equivalent to Clang?
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> </span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Thanks,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> </span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">--
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">John Dallman<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">DF PL TO OT PC PDE<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Technology & Innovation<o:p></o:p></span></p>
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<p class="MsoNormal"><i><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Nullius in verba</span></i><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> </span><span style="font-size:10.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Siemens Industry Sector<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Siemens Industry Software Limited
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Francis House, 112 Hills Road,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Cambridge CB2 1PH, United Kingdom
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Tel. :+44 (1223) 371554<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Calibri","sans-serif"">Fax :+44 (1223) 371700<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><a href="mailto:john.dallman@siemens.com"><span style="color:#0563C1">john.dallman@siemens.com
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">-----------------<br>
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