From: Dave Hansen <dave.hansen@intel.com>
To: "Chen, Yian" <yian.chen@intel.com>,
Sohil Mehta <sohil.mehta@intel.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Ravi Shankar <ravi.v.shankar@intel.com>,
Tony Luck <tony.luck@intel.com>, Paul Lai <paul.c.lai@intel.com>
Subject: Re: [PATCH 3/7] x86/cpu: Disable kernel LASS when patching kernel alternatives
Date: Wed, 11 Jan 2023 16:37:17 -0800 [thread overview]
Message-ID: <b9e73d06-bd95-7c54-3ff1-f9e43c9967a4@intel.com> (raw)
In-Reply-To: <ad2da884-c8c8-bc57-e21f-452a08cb10cc@intel.com>
On 1/11/23 16:27, Chen, Yian wrote:
>> It seems we are implicitly relying on the on stac() and clac()
>> calls that are added for SMAP. Have you tried running with SMAP
>> disabled i.e "clearcpuid=smap"?
>>
> Yes, I tested with clearcpuid=smap.
It works by accident, then.
clearcpuid=smap means that the kernel should be running as if
CPUID.(EAX=07H,ECX=0H):EBX.SMAP[bit 20]==0. STAC/CLAC should #UD in
that case.
The only reason that it happens to work is that STAC/CLAC apparently
actually continue to work even if CR4.SMAP==0.
I'm actually a _bit_ surprised by this, but I bet there's a good reason
for it.
In any case, please just make LASS dependent on SMAP. It's the right
thing to do on several levels.
next prev parent reply other threads:[~2023-01-12 0:38 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-10 5:51 [PATCH 0/7] Enable LASS (Linear Address space Separation) Yian Chen
2023-01-10 5:51 ` [PATCH 1/7] x86/cpu: Enumerate LASS CPUID and CR4 bits Yian Chen
2023-01-10 20:14 ` Sohil Mehta
2023-01-11 0:13 ` Dave Hansen
2023-01-11 23:23 ` Chen, Yian
2023-01-12 0:06 ` Luck, Tony
2023-01-12 0:15 ` Chen, Yian
2023-01-11 19:21 ` Chen, Yian
2023-01-10 5:51 ` [PATCH 2/7] x86: Add CONFIG option X86_LASS Yian Chen
2023-01-10 21:05 ` Sohil Mehta
2023-01-12 0:13 ` Chen, Yian
2023-01-10 5:52 ` [PATCH 3/7] x86/cpu: Disable kernel LASS when patching kernel alternatives Yian Chen
2023-01-10 21:04 ` Peter Zijlstra
2023-01-11 1:01 ` Chen, Yian
2023-01-11 9:10 ` Peter Zijlstra
2023-01-10 22:41 ` Sohil Mehta
2023-01-12 0:27 ` Chen, Yian
2023-01-12 0:37 ` Dave Hansen [this message]
2023-01-12 18:36 ` Chen, Yian
2023-01-12 18:48 ` Dave Hansen
2023-02-01 2:25 ` Sohil Mehta
2023-02-01 18:20 ` Dave Hansen
2023-02-01 2:10 ` Sohil Mehta
2023-01-10 5:52 ` [PATCH 4/7] x86/vsyscall: Setup vsyscall to compromise LASS protection Yian Chen
2023-01-11 0:34 ` Sohil Mehta
2023-01-12 1:43 ` Chen, Yian
2023-01-12 2:49 ` Sohil Mehta
2023-01-21 4:09 ` Andy Lutomirski
2023-01-10 5:52 ` [PATCH 5/7] x86/cpu: Enable LASS (Linear Address Space Separation) Yian Chen
2023-01-11 22:22 ` Sohil Mehta
2023-01-12 17:56 ` Chen, Yian
2023-01-12 18:17 ` Dave Hansen
2023-01-13 1:17 ` Sohil Mehta
2023-01-13 19:39 ` Sohil Mehta
2023-01-10 5:52 ` [PATCH 6/7] x86/cpu: Set LASS as pinning sensitive CR4 bit Yian Chen
2023-01-10 5:52 ` [PATCH 7/7] x86/kvm: Expose LASS feature to VM guest Yian Chen
2023-02-07 3:21 ` Wang, Lei
2023-02-09 17:18 ` Sean Christopherson
2023-01-10 19:48 ` [PATCH 0/7] Enable LASS (Linear Address space Separation) Sohil Mehta
2023-01-10 22:57 ` Dave Hansen
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