linux-kernel - Re: [PATCHv8 03/17] x86/alternatives: Disable LASS when patching kernel alternatives

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fd8c912c-89d4-4933-a3f8-f0a38a3c3482@intel.com>
Date: Tue, 1 Jul 2025 11:44:04 -0700
From: Sohil Mehta <sohil.mehta@...el.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>, 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>, Vegard Nossum
	<vegard.nossum@...cle.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: [PATCHv8 03/17] x86/alternatives: Disable LASS when patching
 kernel alternatives

On 7/1/2025 2:58 AM, Kirill A. Shutemov wrote:
>  
> +/*
> + * The CLAC/STAC instructions toggle the enforcement of X86_FEATURE_SMAP and
> + * X86_FEATURE_LASS.
> + *
> + * SMAP enforcement is based on the _PAGE_BIT_USER bit in the page tables: the
> + * kernel is not allowed to touch pages with the bit set unless the AC bit is
> + * set.
> + *
> + * LASS enforcement is based on bit 63 of the virtual address. The kernel is
> + * not allowed to touch memory in the lower half of the virtual address space
> + * unless the AC bit is set.
> + *
> + * Use stac()/clac() when accessing userspace (_PAGE_USER) mappings,
> + * regardless of location.
> + *
> + * Use lass_stac()/lass_clac() when accessing kernel mappings (!_PAGE_USER)
> + * in the lower half of the address space.
> + *
> + * Note: a barrier is implicit in alternative().
> + */
> +
Thank you for incorporating my feedback. I like the updated wording.