linux-kernel - Re: [PATCHv7 00/16] x86: Enable Linear Address Space Separation support

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Message-ID: <0d315950-89d3-4fd1-acfa-d38c9190b36b@oracle.com>
Date: Thu, 26 Jun 2025 15:15:36 +0200
From: Vegard Nossum <vegard.nossum@...cle.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Xiongwei Song <xiongwei.song@...driver.com>,
        Xin Li <xin3.li@...el.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Michael Roth <michael.roth@....com>, Tony Luck <tony.luck@...el.com>,
        Alexey Kardashevskiy <aik@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>, Sohil Mehta <sohil.mehta@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Kai Huang <kai.huang@...el.com>, Sandipan Das <sandipan.das@....com>,
        Breno Leitao <leitao@...ian.org>,
        Rick Edgecombe
 <rick.p.edgecombe@...el.com>,
        Alexei Starovoitov <ast@...nel.org>, Hou Tao <houtao1@...wei.com>,
        Juergen Gross <jgross@...e.com>, Kees Cook <kees@...nel.org>,
        Eric Biggers <ebiggers@...gle.com>, Jason Gunthorpe <jgg@...pe.ca>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>, Yuntao Wang <ytcoode@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Tejun Heo <tj@...nel.org>, Changbin Du <changbin.du@...wei.com>,
        Huang Shijie <shijie@...amperecomputing.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv7 00/16] x86: Enable Linear Address Space Separation
 support


On 26/06/2025 14:47, Kirill A. Shutemov wrote:
> On Thu, Jun 26, 2025 at 11:35:21AM +0200, Vegard Nossum wrote:
>> On 26/06/2025 11:22, Vegard Nossum wrote:
>>> On 25/06/2025 14:50, Kirill A. Shutemov wrote:
>>>> Linear Address Space Separation (LASS) is a security feature that
>>>> intends to
>>>> prevent malicious virtual address space accesses across user/kernel mode.
>>>
>>> I applied these patches on top of tip/master and when I try to boot it
>>> fails with errno 12 (ENOMEM - Cannot allocate memory):
>>>
>>> [    1.517526] Kernel panic - not syncing: Requested init /bin/bash
>>> failed (error -12).
> 
> For some reason, I failed to reproduce it. What is your toolchain?

$ gcc --version
gcc (GCC) 11.4.1 20230605 (Red Hat 11.4.1-2.1.0.1)

I tried to diff vmlinux with and without the clobber change and I see a
bunch of changed functions, the first one I looked at is calling
put_user() -- I guess anything could be affected, really.

>> @@ -28,7 +28,7 @@ static __always_inline void *__inline_memcpy(void *to,
>> const void *from, size_t
>>                       "2:\n\t"
>>                       _ASM_EXTABLE_UA(1b, 2b)
>>                       :"+c" (len), "+D" (to), "+S" (from),
>> ASM_CALL_CONSTRAINT
>> -                    : : "memory", _ASM_AX);
>> +                    : : "memory", _ASM_AX, _ASM_DX);
>>
>>          return ret + len;
>>   }
> 
> This part is not needed. rep_movs_alternative() doesn't touch RDX.

True, I didn't look closely enough...

> I will fold the patch below.

Thanks,


Vegard