Messages in this thread | | | From | Matthias Welwarsky <> | Subject | Re: x86, possible bug in __memmove() alternatives patching | Date | Sat, 26 Mar 2022 12:39:23 +0100 |
| |
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
| |