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Date:   Mon, 23 Mar 2020 15:32:28 +0000
From:   Mark Brown <broonie@kernel.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        Will Deacon <will@kernel.org>,
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        Peter Zijlstra <peterz@infradead.org>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Amit Kachhap <amit.kachhap@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Marc Zyngier <maz@kernel.org>,
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        "H . J . Lu " <hjl.tools@gmail.com>,
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Subject: Re: [PATCH v10 00/13] arm64: Branch Target Identification support
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On Mon, Mar 23, 2020 at 02:55:46PM +0000, Mark Rutland wrote:
> On Mon, Mar 23, 2020 at 02:39:55PM +0000, Catalin Marinas wrote:

> > So this means that the interpreter will have to mprotect(PROT_BTI) the
> > text section of the primary executable.

> Yes, but after fixing up any relocations in that section it's going to
> have to call mprotect() on it anyhow (e.g. in order to make it
> read-only), and in doing so would throw away BTI unless it was BTI
> aware.

Ah, of course - I forgot that's not a read/modify/write cycle.  I'll
send the comment version.

> > That's a valid point. If we have an old dynamic linker and the kernel
> > enabled BTI automatically for the main executable, could things go wrong
> > (e.g. does the PLT need to be BTI-aware)?

> I believe that a PLT in an unguarded page needs no special treatment. A
> PLT within a guarded page needs to be built specially for BTI.

Unguarded stuff is unaffected.

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