linux-kernel - Re: [PATCH v5 11/16] x86/vsyscall: Document the fact that vsyscall=emulate disables LASS

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: <576e3c53-6417-4027-8d4c-b9f5703b634f@intel.com>
Date: Tue, 29 Oct 2024 16:41:51 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: Alexander Shishkin <alexander.shishkin@...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>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Alexey Kardashevskiy <aik@....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>, Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v5 11/16] x86/vsyscall: Document the fact that
 vsyscall=emulate disables LASS

On 10/28/2024 9:07 AM, Alexander Shishkin wrote:
> Since EMULATE mode of vsyscall disables LASS, because fixing the LASS
> violations during the EMULATE mode would need complex instruction
> decoding, document this fact in kernel-parameters.txt.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Suggested-by: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 

It might be better to combine this patch with the previous one. Both the
patches are small enough and related to the same thing.

> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1518343bbe22..4091dc48670a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7391,7 +7391,9 @@
>  
>  			emulate     Vsyscalls turn into traps and are emulated
>  			            reasonably safely.  The vsyscall page is
> -				    readable.
> +				    readable.  This also disables the LASS
> +				    feature to allow userspace to poke around
> +				    the vsyscall page.
>  

I am not sure if the person reading this guide would be aware of LASS.
Also the way the sentence is structured it might be easy to misinterpret
its meaning.

How about something like:

emulate     Vsyscalls turn into traps and are emulated
            reasonably safely.  The vsyscall page is
	    readable.  This disables the linear
	    address space separation (LASS) security
	    feature and makes the system less secure.


>  			xonly       [default] Vsyscalls turn into traps and are
>  			            emulated reasonably safely.  The vsyscall