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

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Message-ID: <1b96b0ca-5c14-4271-86c1-c305bf052b16@oracle.com>
Date: Thu, 26 Jun 2025 11:35:21 +0200
From: Vegard Nossum <vegard.nossum@...cle.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>
Cc: 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 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).
> 
> Just using standard defconfig and booting in qemu/KVM with 2G RAM.
> 
> Bisect lands on "x86/asm: Introduce inline memcpy and memset".

I think the newly added mulq to rep_stos_alternative clobbers %rdx, at
least this patch fixed it for me:

diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
index 5cd0f18a431fe..bc096526432a1 100644
--- a/arch/x86/include/asm/string.h
+++ b/arch/x86/include/asm/string.h
@@ -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;
  }
@@ -44,7 +44,7 @@ static __always_inline void *__inline_memset(void 
*addr, int v, size_t len)
                      _ASM_EXTABLE_UA(1b, 2b)
                      : "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT
                      : "a" ((uint8_t)v)
-                    : "memory", _ASM_SI);
+                    : "memory", _ASM_SI, _ASM_DX);

         return ret + len;
  }
diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index ca94828def624..77cfd75718623 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -64,6 +64,7 @@ EXPORT_SYMBOL_GPL(clear_page_erms)
   *
   * Output:
   * rcx: uncleared bytes or 0 if successful.
+ * rdx: clobbered
   */
  SYM_FUNC_START(rep_stos_alternative)
         ANNOTATE_NOENDBR

Thanks,


Vegard