linux-kernel - Re: [BUG][PATCH] arm64: bti: fix BTI to handle local indirect branches

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Message-ID: <20201005202840.GJ5139@sirena.org.uk>
Date:   Mon, 5 Oct 2020 21:28:40 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
        ardb@...nel.org, will@...nel.org, catalin.marinas@....com,
        davem@...emloft.net, herbert@...dor.apana.org.au,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG][PATCH] arm64: bti: fix BTI to handle local indirect
 branches

On Mon, Oct 05, 2020 at 03:10:42PM -0500, Jeremy Linton wrote:
> On 10/5/20 2:59 PM, Mark Brown wrote:

> > ...this is going to cause problems, SYM_CODE means that we should
> > assemble *exactly* what was written since it's some non-standard thing -
> > we use it for the vectors table for example.  Looking at the code it's
> > not 100% clear that the best approach here isn't just to change the call
> > to a regular function call, this isn't a fast path or anything as far as
> > I can see so it's unclear to me why we need to tail call.

> Well for some workloads its could be AFAIK. OTOH, Ard mentioned dumping the
> tail call too, and I think that is pretty reasonable. So it looks like that
> is a better plan since it also avoids all this SYM_ flailing.

Yeah, I think that's the easiest thing all round.

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