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<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">Hi All,<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">Jump Oriented Programming attacks rely on tampering addresses used by indirect call / jmp, e.g. redirect control-flow to non-programmer intended bytes in binary.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">A new target independent command line option –fcf-protection=<branch/return/full/none> instruments control flow protection schemes to handle such attacks.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">X86 Supports Indirect Branch Tracking (IBT) as part of Control-Flow Enforcement Technology (CET).<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">IBT instruments ENDBR instructions (when –fcf-protection=branch is asserted) used to specify valid targets of indirect call / jmp.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">The `nocf_check` attribute indicates that no control-flow check will be performed on the attributed entity.
<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">It disables -fcf-protection=<> for a specific entity to fine grain the HW control flow protection mechanism.
<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">The flag is target independent and currently appertains to a function or function pointer.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">The `nocf_check` attribute has two roles in the context of X86 IBT technology:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:22.5pt;text-indent:-18.0pt;line-height:20.4pt;mso-list:l0 level1 lfo1;background:white">
<![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Appertains to a function - do not add ENDBR instruction at the beginning of the function.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:22.5pt;text-indent:-18.0pt;line-height:20.4pt;mso-list:l0 level1 lfo1;background:white">
<![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Appertains to a function pointer - do not track the target function of this pointer by adding nocf_check prefix to the indirect-call instruction.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">When the CPU decodes `nocf_check` prefix, it will not update IBT state machine, hence, the target addresses of the following indirect jump will not be tracked.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">The naming convention and implementation follow GCC.<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">I will be happy to address any concerns raised by the community regarding the attribute.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">Cheers,<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:9.0pt;background:white">Oren<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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