From: Matthias Welwarsky <matthias.welwarsky@sysgo.com>
To: Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>
Cc: linux-kernel@vger.kernel.org, x86-ml <x86@kernel.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: x86, possible bug in __memmove() alternatives patching
Date: Sat, 26 Mar 2022 12:39:23 +0100 [thread overview]
Message-ID: <3346653.QJadu78ljV@linux-3513> (raw)
In-Reply-To: <d9d0405e-b118-b028-d26f-fbb8de4e7a0e@intel.com>
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
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next prev parent reply other threads:[~2022-03-26 11:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-25 8:51 x86, possible bug in __memmove() alternatives patching Matthias Welwarsky
2022-03-25 22:07 ` Borislav Petkov
2022-03-26 4:45 ` Dave Hansen
2022-03-26 8:27 ` Borislav Petkov
2022-03-29 22:34 ` Dave Hansen
2022-03-26 11:39 ` Matthias Welwarsky [this message]
2022-03-29 22:33 ` Dave Hansen
2022-03-30 13:56 ` Matthias Welwarsky
2022-03-30 14:44 ` Dave Hansen
2022-03-30 14:54 ` Borislav Petkov
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