[edk2-devel] How to guard CAR's stack overflow
Brian J. Johnson
brian.johnson at hpe.com
Thu Sep 22 21:06:41 UTC 2022
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.
Hope that helps. This is mostly theoretical. I don't actually have a
lot of experience with x86 segment programming.
Brian J. Johnson
------------------------------------------------------------------------
*From:* Tiger Liu(BJ-RD) [mailto:TigerLiu at zhaoxin.com]
*Sent:* Wednesday, September 21, 2022, 10:32 PM
*To:* devel at edk2.groups.io <devel at edk2.groups.io>, Ni, Ray
<ray.ni at intel.com>, brian.johnson at hpe.com <brian.johnson at hpe.com>
*Subject:* [edk2-devel] How to guard CAR's stack overflow
> 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 at hpe.com
> *发送时间:*2022年9月20日7:10
> *收件人:*devel at edk2.groups.io; ray.ni at intel.com; Tiger Liu(BJ-RD)
> <TigerLiu at zhaoxin.com
> *抄送:*Fan, Jeff <fanjianfeng at 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 at intel.com <mailto:ray.ni at intel.com>]
>
> *Sent:*Wednesday, September 14, 2022, 10:25 PM
>
> *To:*devel at edk2.groups.io <devel at edk2.groups.io>
> <mailto:devel at edk2.groups.io>, tigerliu at zhaoxin.com
> <tigerliu at zhaoxin.com> <mailto:tigerliu at zhaoxin.com>
>
> *Cc:*Fan, Jeff <fanjianfeng at byosoft.com.cn>
> <mailto:fanjianfeng at 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 at edk2.groups.io <devel at edk2.groups.io>
> <mailto:devel at edk2.groups.io> *On Behalf Of *Tiger Liu(BJ-RD)
> *Sent:* Thursday, September 15, 2022 8:50 AM
> *To:* devel at 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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