From: Mathias Krause <minipli@grsecurity.net>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] x86/cpufeatures: Make X86_FEATURE_SHSTK clearcpuid-able
Date: Fri, 15 May 2026 18:11:46 +0200 [thread overview]
Message-ID: <a3bf1f73-2f17-4745-8693-c9336e9010d1@grsecurity.net> (raw)
In-Reply-To: <20260514165922.GGagX_amNCc0mZcz4d@fat_crate.local>
On 5/14/26 18:59, Borislav Petkov wrote:
> On Thu, May 14, 2026 at 06:09:32PM +0200, Mathias Krause wrote:
>> Allow X86_FEATURE_SHST to be disabled through the kernel commandline via
>> 'clearcpuid=shstk' as 'nousershstk' would still enable CR4.CET even if
>> no CET features are in use.
>
> clearcpuid= taints the kernel because that cmdline option is not supposed to
> be used except for debugging crap... and alas people are still using it. No
> wonder... :-\
Funny to see how x86 maintainer options completely disagree on this, see
https://lore.kernel.org/lkml/739e4dd0-84a3-4b37-8cc3-b7ec59737010@intel.com/
>
> Anyway, "nousershstk" should disable the CR4 bit too.
>
No, it should not, as that's only for the user portion
(X86_FEATURE_USER_SHSTK != X86_FEATURE_SHSTK).
Even though there is (currently) no kernel level shadow stack support,
KVM may still want to pass it down to guests for their usage -- even if
the host *userland* shouldn't make use of it because of "nousershstk".
Thanks,
Mathias
next prev parent reply other threads:[~2026-05-15 16:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-14 16:09 Mathias Krause
2026-05-14 16:59 ` Borislav Petkov
2026-05-14 17:07 ` Edgecombe, Rick P
2026-05-14 17:12 ` Borislav Petkov
2026-05-14 17:15 ` Borislav Petkov
2026-05-14 18:23 ` Edgecombe, Rick P
2026-05-14 22:38 ` Borislav Petkov
2026-05-15 16:20 ` Mathias Krause
2026-05-14 17:30 ` Dave Hansen
2026-05-14 18:25 ` Edgecombe, Rick P
2026-05-15 16:11 ` Mathias Krause [this message]
2026-05-15 16:21 ` Edgecombe, Rick P
2026-05-16 15:27 ` Borislav Petkov
2026-05-19 21:08 ` Mathias Krause
2026-05-14 17:01 ` Edgecombe, Rick P
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