linux-kernel - Re: [PATCH 4/5] iommu: Regulate errno in ->attach

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <YyGjtsB2Yq4fQICS@myrica>
Date:   Wed, 14 Sep 2022 10:49:42 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Nicolin Chen <nicolinc@...dia.com>, joro@...tes.org,
        suravee.suthikulpanit@....com, will@...nel.org,
        robin.murphy@....com, robdclark@...il.com, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, agross@...nel.org,
        bjorn.andersson@...aro.org, konrad.dybcio@...ainline.org,
        matthias.bgg@...il.com, heiko@...ech.de, orsonzhai@...il.com,
        baolin.wang@...ux.alibaba.com, zhang.lyra@...il.com,
        thierry.reding@...il.com, sricharan@...eaurora.org,
        yong.wu@...iatek.com, vdumpa@...dia.com, jonathanh@...dia.com,
        tglx@...utronix.de, shameerali.kolothum.thodi@...wei.com,
        thunder.leizhen@...wei.com, christophe.jaillet@...adoo.fr,
        yangyingliang@...wei.com, jon@...id-run.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-tegra@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 4/5] iommu: Regulate errno in ->attach_dev callback
 functions

On Wed, Sep 14, 2022 at 06:11:06AM -0300, Jason Gunthorpe wrote:
> On Tue, Sep 13, 2022 at 01:27:03PM +0100, Jean-Philippe Brucker wrote:
> > I think in the future it will be too easy to forget about the constrained
> > return value of attach() while modifying some other part of the driver,
> > and let an external helper return EINVAL. So I'd rather not propagate ret
> > from outside of viommu_domain_attach() and finalise().
> 
> Fortunately, if -EINVAL is wrongly returned it only creates an
> inefficiency, not a functional problem. So we do not need to be
> precise here.

Ah fair. In that case the attach_dev() documentation should indicate that
EINVAL is a hint, so that callers don't rely on it (currently words "must"
and "exclusively" indicate that returning EINVAL for anything other than
device-domain incompatibility is unacceptable). The virtio-iommu
implementation may well return EINVAL from the virtio stack or from the
host response.

Thanks,
Jean

> 
> > Since we can't guarantee that APIs like virtio or ida won't ever return
> > EINVAL, we should set all return values:
> 
> I dislike this alot, it squashes all return codes to try to optimize
> an obscure failure path :(
> 
> Jason