Re: [edk2-devel] How to guard CAR's stack overflow

["Tiger Liu(BJ-RD)" <tigerliu@zhaoxin.com>]

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Hi, Johnson:
Thanks for your reply!

I tried and found it seemed causing some other problems.

It hang in eary pei stage.

It seems below code could also cause an exception if using expand-down mode in CAR phase’s stack established.
mov eax, ss:[ebx]
 mov eax, [ebp]
  mov eax, [esp]

Thanks
发件人: Brian J. Johnson <brian.johnson@hpe.com<mailto:brian.johnson@hpe.com>>
发送时间: 2022年9月20日 7:10
收件人: devel@edk2.groups.io<mailto:devel@edk2.groups.io>; ray.ni@intel.com<mailto:ray.ni@intel.com>; Tiger Liu(BJ-RD) <TigerLiu@zhaoxin.com<mailto:TigerLiu@zhaoxin.com>>
抄送: Fan, Jeff <fanjianfeng@byosoft.com.cn<mailto:fanjianfeng@byosoft.com.cn>>
主题: Re: [edk2-devel] How to guard CAR's stack overflow

You could also try modifying the Ia32 segment descriptors to mark the stack segment as an "expand down" type with a limit set just below the low end of the stack area.  That should generate a stack-fault exception if the stack overflows, and wouldn't require building page tables.  See sections 5.1 - 5.3 of the Intel SDM, volume 3.

Brian J. Johnson

________________________________
From: Ni, Ray [mailto:ray.ni@intel.com]
Sent: Wednesday, September 14, 2022, 10:25 PM
To: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io><mailto:devel@edk2.groups.io>, tigerliu@zhaoxin.com<mailto:tigerliu@zhaoxin.com> <tigerliu@zhaoxin.com><mailto:tigerliu@zhaoxin.com>
Cc: Fan, Jeff <fanjianfeng@byosoft.com.cn><mailto:fanjianfeng@byosoft.com.cn>
Subject: [edk2-devel] How to guard CAR's stack overflow

It’s doable.
You need to enable paging and mark the very low 4K area of the stack as not-present.
You could use the UefiCpuPkg/Library/CpuPageTableLib to help you create the 1:1 page table with the specific
4K area as not-present (if you are using x86 processors).

Thanks,
Ray

From: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io><mailto:devel@edk2.groups.io> On Behalf Of Tiger Liu(BJ-RD)
Sent: Thursday, September 15, 2022 8:50 AM
To: devel@edk2.groups.io<mailto:devel@edk2.groups.io>
Subject: [edk2-devel] How to guard CAR's stack overflow

Hi, Experts:
Usually, we use Cache As Ram to setup stack and heap for C language running environment before permanent memory has been initialized.

So, is there a method to guard this phase’s stack overflow?

Note:
I find udk has introduced a method to guard stack overflow after memory has been initialized and discovered.

Thanks

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