linux-kernel - Re: [PATCH v1 1/1] x86/fred: Fix the FRED RSP0 MSR out of sync with its per CPU cache

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] [day] [month] [year] [list]

Message-ID: <a132c883-8399-4936-9f28-0fc28db22641@zytor.com>
Date: Thu, 9 Jan 2025 10:48:32 -0800
From: Xin Li <xin@...or.com>
To: "H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, andrew.cooper3@...rix.com
Subject: Re: [PATCH v1 1/1] x86/fred: Fix the FRED RSP0 MSR out of sync with
 its per CPU cache

On 1/9/2025 1:46 AM, H. Peter Anvin wrote:
> On January 8, 2025 12:14:18 PM PST, Dave Hansen <dave.hansen@...el.com> wrote:
>> On 1/7/25 18:36, Xin Li (Intel) wrote:
>>> +	 * Another option is to leave the FRED RSP0 MSR as-is, because the RESET
>>> +	 * state of FRED MSRs is zero and INIT does not change the value of the
>>> +	 * FRED MSRs in a CPU offline/online cycle.  But it doesn't seem safe to
>>> +	 * depend on the properties of INIT as that's way too many things that
>>> +	 * could cause bugs.
>>
>> Wouldn't that also open us up to kexec problems? If the last kernel
>> (maybe not even Linux) left RSP0 set, then the current kernel might
>> eventually try to run userspace with the old kernel's RSP0 value.
>>
> 
> Yeah, it is a nonstarter. I believe Xin was trying to document the problems with *not* doing this, so someone doesn't have the bright idea to "optimize" this later.
> 

exactly ;)