linux-kernel - Re: [RFC PATCH 0/2] Branch Target Injection (BTI) gadget in minstrel

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Message-ID: <Y1hHhMczQlqi4DxD@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Oct 2022 22:31:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     scott.d.constable@...el.com, daniel.sneddon@...ux.intel.com,
        Jakub Kicinski <kuba@...nel.org>, dave.hansen@...el.com,
        Johannes Berg <johannes@...solutions.net>,
        Paolo Abeni <pabeni@...hat.com>,
        antonio.gomez.iglesias@...ux.intel.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, gregkh@...uxfoundation.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Branch Target Injection (BTI) gadget in minstrel

On Tue, Oct 25, 2022 at 12:38:45PM -0700, Pawan Gupta wrote:

> > I think the focus should be on finding the source sites, not protecting
> > the target sites. Where can an attacker control the register content and
> > have an indirect jump/call.
> 
> That is an interesting approach. I am wondering what mitigation can
> be applied at source?

Limiting the value ranges for example. Or straight up killing the values
if they go unused -- like how we clear the registers in entry.

> LFENCE before an indirect branch can greatly
> reduce the speculation window, but will not completely eliminate it.

Depends on the part; there's a whole bunch of parts where LFENCE is
sufficient.