linux-kernel - Re: [PATCH v9 3/3] x86/snp: Convert shared memory back to private on kexec

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f4f780b6-d55b-3342-977b-6b217ab19b1d@amd.com>
Date: Fri, 28 Jun 2024 09:01:30 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kalra, Ashish" <ashish.kalra@....com>, Borislav Petkov <bp@...en8.de>
Cc: tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 x86@...nel.org, rafael@...nel.org, hpa@...or.com, peterz@...radead.org,
 adrian.hunter@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 jun.nakajima@...el.com, rick.p.edgecombe@...el.com, michael.roth@....com,
 seanjc@...gle.com, kai.huang@...el.com, bhe@...hat.com,
 kirill.shutemov@...ux.intel.com, bdas@...hat.com, vkuznets@...hat.com,
 dionnaglaze@...gle.com, anisinha@...hat.com, jroedel@...e.de,
 ardb@...nel.org, dyoung@...hat.com, kexec@...ts.infradead.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 3/3] x86/snp: Convert shared memory back to private on
 kexec

On 6/27/24 23:27, Kalra, Ashish wrote:
> Hello Boris,
> 
> On 6/24/2024 10:59 PM, Borislav Petkov wrote:
>> On Mon, Jun 24, 2024 at 03:57:34PM -0500, Kalra, Ashish wrote:
>>> ...  Hence, added simple static functions make_pte_private() and
>>> set_pte_enc() to make use of the more optimized snp_set_memory_private() to
>>> use the GHCB instead of the MSR protocol. Additionally, make_pte_private()
>>> adds check for GHCB addresses during unshare_all_memory() loop.
>> IOW, what you're saying is: "Boris, what you're asking can't be done."
>>
>> Well, what *you're* asking - for me to maintain crap - can't be done either.
>> So this will stay where it is.
>>
>> Unless you make a genuine effort and refactor the code...
> 
> There is an issue with calling __set_clr_pte_enc() here for the _bss_decrypted section being made private again,
> 
> when calling __set_clr_pte_enc() on _bss_decrypted section pages, clflush_cache_range() will fail as __va()
> 
> on this physical range fails as the bss_decrypted section pages are not in kernel direct map.
> 
> Hence, clflush_cache_range() in __set_clr_pte_enc() causes an implicit page state change which is not resolved as below and causes fatal guest exit :
> 
> qemu-system-x86_64: warning: memory fault: GPA 0x4000000 size 0x1000 flags 0x8 kvm_convert_memory start 0x4000000 size 0x1000 shared_to_private
> 
> ...
> 
> KVM: unknown exit reason 24 EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000 ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000 EIP=00000000 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> 
> ...
> 
> This is the reason why i had to pass the vaddr to set_pte_enc(), added here for kexec code, so that i can use it for clflush_cache_range().
> 
> So for specific cases such as this, where we can't call __set_clr_pte_enc() on _bss_decrypted section, we probably need a separate set_pte_enc().

You can probably add a va parameter, that when not NULL, is used for the
flush. If NULL, then use the __va() macro on the pa.

Thanks,
Tom

> 
> Thanks, Ashish
>