lkml.org 
[lkml]   [2022]   [Mar]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: x86, possible bug in __memmove() alternatives patching
Date
On Samstag, 26. März 2022 05:45:24 CET Dave Hansen wrote:
> On 3/25/22 15:07, Borislav Petkov wrote:
> > I know it's is probably a very rare case and Intel recommends having fast
> > string ops enabled, hence the question: would this be considered a bug in
> > the kernel that should be fixed? A potential fix could be to clear FSRM
> > together with ERMS depending on IA32_MISC_ENABLE.
>
> I'd consider it a bug in the hypervisor, personally. ;)

Of course, no doubt about that.

> But, we do try to make the kernel work even the face of funky
> hypervisors that do things that never occur on real hardware. If a nice
> patch to fix this up showed up, I'd definitely take a look.

The question is whether a sequence like this could be relevant:

0) CPU announces feature FSRM through cpuid
1) BIOS/firmware disables fast string ops through IA32_MISC_ENABLE before
loading kernel (for whatever reason)
2) Kernel populates features from cpuid
3) Kernel clears ERMS based on IA32_MISC_ENABLE
4) "alternatives" patching destroys __memmove()

That depends on whether a cpuid instruction after step 1) would still announce
FSRM. If not, then the whole point is moot and no patch needed (unless we want
to guard against hypervisor bugs).

--
Mit freundlichen Grüßen/Best regards,

Matthias Welwarsky
Project Engineer

SYSGO GmbH
Office Mainz
Am Pfaffenstein 8 / D-55270 Klein-Winternheim / Germany
Phone: +49-6136-9948-0 / Fax: +49-6136-9948-10
E-mail: matthias.welwarsky@sysgo.com
_________________________________________________________________________________
Web: https://www.sysgo.com
Blog: https://www.sysgo.com/blog
Events: https://www.sysgo.com/events
Newsletter: https://www.sysgo.com/newsletter
_________________________________________________________________________________
Handelsregister/Commercial Registry: HRB Mainz 90 HRB 48884
Geschäftsführung/Managing Directors: Etienne Butery (CEO), Kai Sablotny (COO)
USt-Id-Nr./VAT-Id-No.: DE 149062328

The protection of your personal data is important to us. Under the following
link
you can see the information in accordance with article 13 GDPR:
https://www.sysgo.com/privacy_policy


\
 
 \ /
  Last update: 2022-03-26 12:40    [W:0.059 / U:2.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site