linux-kernel - Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS

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: <bbe9dfb6-88c7-4724-bafd-0524599c9369@intel.com>
Date: Wed, 2 Jul 2025 13:05:17 -0700
From: Sohil Mehta <sohil.mehta@...el.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>, "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 14/17] x86/traps: Handle LASS thrown #SS

On 7/2/2025 6:27 AM, Kirill A. Shutemov wrote:

>>
>> Maybe I've misunderstood something:
>>
>> Is the underlying assumption here that #SS were previously only
>> generated by userspace, but now they can also be generated by the
>> kernel? And we want the kernel generated #SS to behave the same as the #GP?
> 
> It can be generated by both kernel and userspace if RSP gets corrupted.
> 
> So far, do_error_trap() did the trick, handling what has to be handled.
> LASS requires a bit more, though.
> 
Thank you for the information! The discussion in the other thread helped
clarify my confusion about the new FRED specific fixup outside the LASS
check.

IIUC, for kernel generated #SS, the prior code in do_error_trap()
would've done a few things such as notify_die() and
cond_local_irq_enable() before calling die().

The new code now directly calls die_addr(). Are we changing the behavior
for legacy kernel #SS? Also, why don't we need those calls for the new
LASS #SS?

I apologize if the questions seem too naive. I am finding the exception
handling code a bit convoluted to understand. In general, I would
suggest adding some code comments at least for the new code to help
ignorant folks like me looking at this in the future.