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: Thu, 12 Jan 2023 10:48:33 -0800 [thread overview]
Message-ID: <f8352c29-6b9f-2711-ddf4-223a6806f42f@intel.com> (raw)
In-Reply-To: <9e0a8b20-cb76-b06d-67fb-f8942df5a2f7@intel.com>
On 1/12/23 10:36, Chen, Yian wrote:
> On 1/11/2023 4:37 PM, Dave Hansen wrote:
>> 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.
>>
> It could be something wrong in my Simics simulation environment.
Also, Andy Cooper made a very good point: when the kernel enables
paging, it's running with a low address so that the instruction pointer
stays valid as paging becomes enabled.
But, if LASS were enabled and enforced at that point, you'd get a LASS
fault and go kablooey. Can you see what simics does in that case, and
also make sure we're clearing CR4.LASS when enabling paging? That would
obviate the need to do it later in C code too.
next prev parent reply other threads:[~2023-01-12 19:08 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
2023-01-12 18:36 ` Chen, Yian
2023-01-12 18:48 ` Dave Hansen [this message]
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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