linux-kernel - Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20171101141603.4ppgwup4grnmcswe@lakrids.cambridge.arm.com>
Date:   Wed, 1 Nov 2017 14:16:33 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     gengdongjiu <gengdongjiu@...wei.com>
Cc:     Robin Murphy <robin.murphy@....com>, catalin.marinas@....com,
        will.deacon@....com, marc.zyngier@....com,
        christoffer.dall@...aro.org, james.morse@....com,
        ard.biesheuvel@...aro.org, cov@...eaurora.org, Dave.Martin@....com,
        suzuki.poulose@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

On Wed, Nov 01, 2017 at 08:54:44PM +0800, gengdongjiu wrote:
> On 2017/11/1 19:24, Robin Murphy wrote:
> >> +	esb
> >> +alternative_else_nop_endif
> >> +1:
> >> +	.endm
> > Having a branch in here is pretty horrible, and furthermore using label
> > number 1 has a pretty high chance of subtly breaking code where this
> > macro is inserted.
> > 
> > Can we not somehow nest or combine the alternative conditions here?
> 
> I found it will report error if combine the alternative conditions here.
> 
> For example:
> 
> +	.macro	error_synchronize
> +alternative_if ARM64_HAS_IESB
> +alternative_if ARM64_HAS_RAS_EXTN
> +	esb
> +alternative_else_nop_endif
> +alternative_else_nop_endif
> +	.endm
> 
> And even using b.eq/cbz instruction in the alternative instruction in arch/arm64/kernel/entry.S,
> it will report Error.

Alternatives cannot be nested. You need to define a cap like:

  ARM64_HAS_RAS_NOT_IESB

... which is set when ARM64_HAS_RAS_EXTN && !ARM64_HAS_IESB.

Then you can do:

alternative_if ARM64_HAS_RAS_NOT_IESB
	esb
alternative_else_nop_endif

See ARM64_ALT_PAN_NOT_UAO for an example.

That said, as Robin points out we may not even need the alternative.

Thanks,
Mark.