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 for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250706101342.069b5068@pumpkin>
Date: Sun, 6 Jul 2025 10:13:42 +0100
From: David Laight <david.laight.linux@...il.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: "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>, 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>, 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 02/17] x86/asm: Introduce inline memcpy and memset

On Thu, 3 Jul 2025 10:13:44 -0700
Dave Hansen <dave.hansen@...el.com> wrote:

> On 7/1/25 02:58, Kirill A. Shutemov wrote:
> > Extract memcpy and memset functions from copy_user_generic() and
> > __clear_user().
> > 
> > They can be used as inline memcpy and memset instead of the GCC builtins
> > whenever necessary. LASS requires them to handle text_poke.  
> 
> Why are we messing with the normal user copy functions? Code reuse is
> great, but as you're discovering, the user copy code is highly
> specialized and not that easy to reuse for other things.
> 
> Don't we just need a dirt simple chunk of code that does (logically):
> 
> 	stac();
> 	asm("rep stosq...");
> 	clac();
> 
> Performance doesn't matter for text poking, right? It could be stosq or
> anything else that you can inline. It could be a for() loop for all I
> care as long as the compiler doesn't transform it into some out-of-line
> memset. Right?
> 

It doesn't even really matter if there is an out-of-line memset.
All you need to do is 'teach' objtool it isn't a problem.

Is this for the boot-time asm-alternatives?
In that case I wonder why a 'low' address is being used?
With LASS enabled using a low address on a life kernel would make it
harder for another cpu to leverage the writable code page, but
that isn't a requirement of LASS.

If it is being used for later instruction patching you need the
very careful instruction sequences and cpu synchronisation.
In that case I suspect you need to add conditional stac/clac
to the existing patching code (and teach objtool it is all ok).

	David

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ