linux-kernel - Re: [PATCH v2 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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]

Date:   Mon, 29 Mar 2021 15:02:15 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

On 3/29/21 2:55 PM, Kuppuswamy, Sathyanarayanan wrote:
>>
>> MONITOR is a privileged instruction, right?  So we can only end up in
>> here if the kernel screws up and isn't reading CPUID correctly, right?
>>
>> That dosen't seem to me like something we want to suppress.  This needs
>> a warning, at least.  I assume that having a MONITOR instruction
>> immediately return doesn't do any harm.
> Agree. Since we are not supposed to come here, I will use BUG.

"This is unexpected" is a WARN()able offense.

"This is unexpected and might be corrupting data" is where we want to
use BUG().

Does broken MONITOR risk data corruption?

>>> +    case EXIT_REASON_MWAIT_INSTRUCTION:
>>> +        /* MWAIT is supressed, not supposed to reach here. */
>>> +        WARN(1, "MWAIT unexpected #VE Exception\n");
>>> +        return -EFAULT;
>>
>> How is MWAIT "supppressed"?
> I am clearing the MWAIT feature flag in early init code. We should also
> disable this feature in firmware. setup_clear_cpu_cap(X86_FEATURE_MWAIT);

I'd be more explicit about that.  Maybe even reference the code that
clears the X86_FEATURE.