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<div class="moz-cite-prefix">
<div class="moz-cite-prefix">I've never tried protecting the stack
like this, so I'm not sure exactly what you're running in to.
The documentation says the base address is specified a bit
differently for expand-down descriptors. It needs to point to
the page below the stack (lower addresses.) The descriptors for
the other segments would still need to cover the entire address
space (limit 0xFFFF, page-granular, expand-up.) And you'd need
to use a different segment selector (and hence a different GDT
entry) for the stack segment (ss register) than for the regular
data segments. Most of the early PEI code I've seen uses the
same selector for ds, ef, fs, gs, and ss.<br>
</div>
<div class="moz-cite-prefix"><br>
<div>Hope that helps. This is mostly theoretical. I don't
actually have a lot of experience with x86 segment
programming.</div>
<div><br>
</div>
<div>Brian J. Johnson<br>
<hr id="rwhMsgHdrDivider" style="border:0;border-top:1px solid
#B5C4DF;padding:0;margin:10px 0 5px 0;width:100%;">
<div style="font-family:sans-serif !important; color:#000000
!important; font-size:11pt !important;"><b>From:</b> Tiger
Liu(BJ-RD) [<a class="moz-txt-link-freetext" href="mailto:TigerLiu@zhaoxin.com">mailto:TigerLiu@zhaoxin.com</a>]</div>
<div style="font-family:sans-serif !important; color:#000000
!important; font-size:11pt !important;"><b>Sent:</b>
Wednesday, September 21, 2022, 10:32 PM</div>
<div style="font-family:sans-serif !important; color:#000000
!important; font-size:11pt !important;"><b>To:</b>
<a class="moz-txt-link-abbreviated" href="mailto:devel@edk2.groups.io">devel@edk2.groups.io</a> <a class="moz-txt-link-rfc2396E" href="mailto:devel@edk2.groups.io"><devel@edk2.groups.io></a>, Ni, Ray
<a class="moz-txt-link-rfc2396E" href="mailto:ray.ni@intel.com"><ray.ni@intel.com></a>, <a class="moz-txt-link-abbreviated" href="mailto:brian.johnson@hpe.com">brian.johnson@hpe.com</a>
<a class="moz-txt-link-rfc2396E" href="mailto:brian.johnson@hpe.com"><brian.johnson@hpe.com></a></div>
<div style="font-family:sans-serif !important; color:#000000
!important; font-size:11pt !important;"><b>Subject:</b>
[edk2-devel] How to guard CAR's stack overflow</div>
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<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US">Hi, Johnson:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US">Thanks for your reply!<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US">I tried and found it
seemed causing some other problems.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US">It hang in eary pei
stage.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:left" align="left"><span style="color:#1F497D" lang="EN-US">It seems below code could
also cause an exception if using expand-down mode in CAR
phase’s stack established.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">mov
eax, ss:[ebx]
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"> mov
eax, [ebp]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
mov eax, [esp]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Thanks<o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal" style="text-align:left" align="left"><b><span style="font-size:11.0pt">发件人<span lang="EN-US">:</span></span></b><span style="font-size:11.0pt" lang="EN-US"> Brian J. Johnson
<<a href="mailto:brian.johnson@hpe.com" moz-do-not-send="true" class="moz-txt-link-freetext">brian.johnson@hpe.com</a>
<br>
</span><b><span style="font-size:11.0pt">发送时间<span lang="EN-US">:</span></span></b><span style="font-size:11.0pt" lang="EN-US"> 2022</span><span style="font-size:11.0pt">年<span lang="EN-US">9</span>月<span lang="EN-US">20</span>日<span lang="EN-US"> 7:10<br>
</span><b>收件人<span lang="EN-US">:</span></b><span lang="EN-US"> <a href="mailto:devel@edk2.groups.io" moz-do-not-send="true" class="moz-txt-link-freetext"> devel@edk2.groups.io</a>; <a href="mailto:ray.ni@intel.com" moz-do-not-send="true" class="moz-txt-link-freetext">ray.ni@intel.com</a>;
Tiger Liu(BJ-RD) <<a href="mailto:TigerLiu@zhaoxin.com" moz-do-not-send="true" class="moz-txt-link-freetext">TigerLiu@zhaoxin.com</a><br>
</span><b>抄送<span lang="EN-US">:</span></b><span lang="EN-US"> Fan, Jeff <<a href="mailto:fanjianfeng@byosoft.com.cn" moz-do-not-send="true" class="moz-txt-link-freetext">fanjianfeng@byosoft.com.cn</a><br>
</span><b>主题<span lang="EN-US">:</span></b><span lang="EN-US"> Re: [edk2-devel] How to guard CAR's
stack overflow<o:p></o:p></span></span></p>
</div>
</div>
<p class="MsoNormal" style="text-align:left" align="left"><span lang="EN-US"><o:p> </o:p></span></p>
<div>
<div id="rwhMsgHeader">
<p class="MsoNormal" style="text-align:left" align="left"><span lang="EN-US">You could also try modifying the Ia32
segment descriptors to
<span style="background:yellow;mso-highlight:yellow">mark
the stack segment as an "expand down" type with a
limit set just below the low end of the stack area</span>.
That should generate a stack-fault exception if the
stack overflows, and wouldn't require building page
tables. <span style="background:aqua;mso-highlight:aqua">See
sections 5.1 - 5.3 of the Intel SDM, volume 3.</span></span><span style="font-size:12.0pt" lang="EN-US"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US">Brian J. Johnson<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<div style="margin-top:7.5pt;margin-bottom:3.75pt">
<div class="MsoNormal" style="text-align:center" align="center"><span lang="EN-US">
<hr width="100%" size="3" align="center">
</span></div>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Ni,
Ray [<a href="mailto:ray.ni@intel.com" moz-do-not-send="true">mailto:ray.ni@intel.com</a>]<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><b><span lang="EN-US">Sent:</span></b><span lang="EN-US">
Wednesday, September 14, 2022, 10:25 PM<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><b><span lang="EN-US">To:</span></b><span lang="EN-US"> <a href="mailto:devel@edk2.groups.io" moz-do-not-send="true" class="moz-txt-link-freetext"> devel@edk2.groups.io</a> <a href="mailto:devel@edk2.groups.io" moz-do-not-send="true"><devel@edk2.groups.io></a>,
<a href="mailto:tigerliu@zhaoxin.com" moz-do-not-send="true" class="moz-txt-link-freetext">tigerliu@zhaoxin.com</a>
<a href="mailto:tigerliu@zhaoxin.com" moz-do-not-send="true"> <tigerliu@zhaoxin.com></a><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><b><span lang="EN-US">Cc:</span></b><span lang="EN-US"> Fan,
Jeff <a href="mailto:fanjianfeng@byosoft.com.cn" moz-do-not-send="true"> <fanjianfeng@byosoft.com.cn></a><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><b><span lang="EN-US">Subject:</span></b><span lang="EN-US">
[edk2-devel] How to guard CAR's stack overflow<o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="mso-margin-top-alt:7.5pt;margin-right:0cm;margin-bottom:3.75pt;margin-left:0cm"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
</div>
<blockquote style="border:none !important; margin-left:0px
!important; margin-right:0px !important; margin-top:0px
!important; padding-left:0px !important; padding-right:0px
!important">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">It’s doable.</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">You need to enable paging and mark the very
low 4K area of the stack as not-present.</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">You could use the
UefiCpuPkg/Library/CpuPageTableLib to help you create the
1:1 page table with the specific<br>
4K area as not-present (if you are using x86 processors).</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US"> </span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">Thanks,</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">Ray</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US"> </span><span lang="EN-US"><o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal" style="text-align:left" align="left"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif" lang="EN-US">
<a href="mailto:devel@edk2.groups.io" moz-do-not-send="true" class="moz-txt-link-freetext">devel@edk2.groups.io</a>
<a href="mailto:devel@edk2.groups.io" moz-do-not-send="true"> <devel@edk2.groups.io></a> <b>On Behalf Of </b>Tiger
Liu(BJ-RD)<br>
<b>Sent:</b> Thursday, September 15, 2022 8:50 AM<br>
<b>To:</b> <a href="mailto:devel@edk2.groups.io" moz-do-not-send="true" class="moz-txt-link-freetext">devel@edk2.groups.io</a><br>
<b>Subject:</b> [edk2-devel] How to guard CAR's stack
overflow</span><span lang="EN-US"><o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal" style="text-align:left" align="left"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Hi, Experts:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Usually, we use Cache
As Ram to setup stack and heap for C language running
environment before permanent memory has been initialized.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">So, is there a method
to guard this phase</span>’<span lang="EN-US">s stack
overflow?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Note:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I find udk has
introduced a method to guard stack overflow after memory
has been initialized and discovered.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt;text-align:left" align="left"><span style="font-size:12.0pt;font-family:宋体" lang="EN-US"> </span><span lang="EN-US"><o:p></o:p></span></p>
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