linux-kernel - Re: [PATCH v8 31/33] x86/fred: BUG() when ERETU with %rsp not equal to that when the ring 3 event was just delivered

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Date:   Mon, 05 Jun 2023 16:15:18 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, peterz@...radead.org, andrew.cooper3@...rix.com,
        seanjc@...gle.com, pbonzini@...hat.com, ravi.v.shankar@...el.com,
        jiangshanlai@...il.com, shan.kang@...el.com
Subject: Re: [PATCH v8 31/33] x86/fred: BUG() when ERETU with %rsp not equal
 to that when the ring 3 event was just delivered

On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
> A FRED stack frame generated by a ring 3 event should never be messed up, and
> the first thing we must make sure is that at the time an ERETU instruction is
> executed, %rsp must have the same address as that when the user level event
> was just delivered.
>
> However we don't want to bother the normal code path of ERETU because it's on
> the hotest code path, a good choice is to do this check when ERETU
> faults.

Which might be not catching bugs where the wrong frame makes ERETU not
fault.

We have CONFIG_DEBUG_ENTRY for catching this at the proper place.

Thanks,

        tglx