linux-kernel - Re: [PATCH 06/24] x86,kvm: Fix indirect calls in emulator

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: <df0ca3ce-3185-d4d7-5467-bee3bbbf7cce@redhat.com>
Date:   Fri, 26 Jan 2018 11:57:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 06/24] x86,kvm: Fix indirect calls in emulator

On 25/01/2018 10:34, Peter Zijlstra wrote:
> On Wed, Jan 24, 2018 at 11:43:05AM +0100, Paolo Bonzini wrote:
>> On 24/01/2018 11:35, Peter Zijlstra wrote:
>>> On Tue, Jan 23, 2018 at 08:48:13PM +0000, David Woodhouse wrote:
>>>> On Tue, 2018-01-23 at 21:28 +0100, Borislav Petkov wrote:
>>>>>
>>>>>>        flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
>>>>>> -     asm("push %[flags]; popf; call *%[fastop]"
>>>>>> -         : "=a"(rc) : [fastop]"r"(fop), [flags]"r"(flags));
>>>>>> +     asm("push %[flags]; popf; " CALL_NOSPEC
>>>>>> +         : "=a"(rc) : [thunk_target]"r"(fop), [flags]"r"(flags));
>>>>>
>>>>> Oh, "thunk_target" is magical.
>>>>
>>>> You can use THUNK_TARGET(fop), which will be "rm" on 32-bit and avoids
>>>> register starvation in some cases (I don't think the hyperv calls
>>>> worked until I did that).
>>>
>>> The reason I didn't use THUNK_TARGET() was exactly because it used "rm"
>>> and the current code did "r" only. I'm happy to change if people can
>>> agree on something ;-)
>>
>> In practice, "fastop" is going to be in a register because of how it's
>> computed, but "rm" is okay.
> 
> OK, so the other occurence in that file uses "+S", which is the SI
> register. That cannot use THUNK_TARGET(), right?

Nope, it reads the output in %esi too.

> So do you want one THUNK_TARGET and one open coded, or keep the patch as
> is (both open coded) ?

Open coded is okay.

Paolo