linux-kernel - Re: [PATCH v2 13/24] drm/etnaviv: reject timeouts with tv_nsec >= NSEC_PER

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Date:   Mon, 20 Jan 2020 18:47:56 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Guido Günther <agx@...xcpu.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>, y2038@...ts.linaro.org,
        etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Emil Velikov <emil.velikov@...labora.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 13/24] drm/etnaviv: reject timeouts with tv_nsec >=
 NSEC_PER_SEC

On Fr, 2020-01-17 at 16:47 +0100, Guido Günther wrote:
> Hi,
> On Fri, Dec 13, 2019 at 09:53:41PM +0100, Arnd Bergmann wrote:
> > Most kernel interfaces that take a timespec require normalized
> > representation with tv_nsec between 0 and NSEC_PER_SEC.
> > 
> > Passing values larger than 0x100000000ull further behaves differently
> > on 32-bit and 64-bit kernels, and can cause the latter to spend a long
> > time counting seconds in timespec64_sub()/set_normalized_timespec64().
> > 
> > Reject those large values at the user interface to enforce sane and
> > portable behavior.
> > 
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  drivers/gpu/drm/etnaviv/etnaviv_drv.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > index 1f9c01be40d7..95d72dc00280 100644
> > --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
> > @@ -297,6 +297,9 @@ static int etnaviv_ioctl_gem_cpu_prep(struct drm_device *dev, void *data,
> >  	if (args->op & ~(ETNA_PREP_READ | ETNA_PREP_WRITE | ETNA_PREP_NOSYNC))
> >  		return -EINVAL;
> >  
> > +	if (args->timeout.tv_nsec > NSEC_PER_SEC)
> > +		return -EINVAL;
> > +
> >  	obj = drm_gem_object_lookup(file, args->handle);
> >  	if (!obj)
> >  		return -ENOENT;
> > @@ -360,6 +363,9 @@ static int etnaviv_ioctl_wait_fence(struct drm_device *dev, void *data,
> >  	if (args->flags & ~(ETNA_WAIT_NONBLOCK))
> >  		return -EINVAL;
> >  
> > +	if (args->timeout.tv_nsec > NSEC_PER_SEC)
> > +		return -EINVAL;
> > +
> >  	if (args->pipe >= ETNA_MAX_PIPES)
> >  		return -EINVAL;
> >  
> > @@ -411,6 +417,9 @@ static int etnaviv_ioctl_gem_wait(struct drm_device *dev, void *data,
> >  	if (args->flags & ~(ETNA_WAIT_NONBLOCK))
> >  		return -EINVAL;
> >  
> > +	if (args->timeout.tv_nsec > NSEC_PER_SEC)
> > +		return -EINVAL;
> > +
> >  	if (args->pipe >= ETNA_MAX_PIPES)
> >  		return -EINVAL;
> > 
> 
> This breaks rendering here on arm64/gc7000 due to
> 
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_PREP or DRM_IOCTL_MSM_GEM_CPU_PREP, 0xfffff7888680) = -1 EINVAL (Invalid argument)
> ioctl(6, DRM_IOCTL_ETNAVIV_GEM_CPU_FINI or DRM_IOCTL_QXL_CLIENTCAP, 0xfffff78885e0) = 0
> 
> This is due to
> 
>     get_abs_timeout(&req.timeout, 5000000000);
> 
> in etna_bo_cpu_prep which can exceed NSEC_PER_SEC.
> 
> Should i send a patch to revert that change since it breaks existing userspace?

No need to revert. This patch has not been applied to the etnaviv tree
yet, I guess it's just in one of Arnds branches feeding into -next.

That part of userspace is pretty dumb, as it misses to renormalize
tv_nsec when it overflows the second boundary. So if what I see is
correct it should be enough to allow 2 * NSEC_PER_SEC, which should
both reject broken large timeout and keep existing userspace working.

Regards,
Lucas