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 May 2018 17:36:55 +0200
Date: Wed, 9 May 2018 17:36:55 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 5/5] SSB extra v2 5
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To: speck@linutronix.de
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On Mon, 7 May 2018, speck for Dave Hansen wrote:
> On 05/07/2018 05:36 PM, speck for Andi Kleen wrote:
> >> +	/* To mitigate speculative-store-bypass, we only need
> >> +	 * mitigation for programs that write to memory.  Mark that
> >> +	 * the program needs mitigation if loaded without
> >> +	 * CAP_SYS_ADMIN:
> >> +	 */
> >> +	if (env->saw_memory_write && !capable(CAP_SYS_ADMIN))
> >> +		env->prog->need_mitigation = true;
> > Flag should have a more descriptive name specific to SSB. 
> > I bet this won't be the last mitigation needed for EBPF :|
> 
> For now, it *is* generic, though.  It's whether the mitigation function
> gets injected into the call path or not.
> 
> Once we have multiple things we have to mitigate for at entry/exit, we
> may need to add some other flags to the bpf_prog that say exactly what
> mitigations we need, like a "bfp_prog->does_memory_write" that
> explicitly tells us if we need the SSB mitigation.

Now looking at the overhead of this SSB hardware mitigation stuff I really
wonder what's the state on investigating software mitigations for BPF.

The magic PDF talks about that, but has anyone looked at that?

Thanks,

	tglx