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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-s390 <linux-s390@vger.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	Jan Kara <jack@suse.cz>, Kees Cook <keescook@chromium.org>,
	KVM list <kvm@vger.kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>,
	LKML <linux-kernel@vger.kernel.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Linux MM <linux-mm@kvack.org>,
	J??r??me Glisse <jglisse@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>
Subject: Re: [PATCH v4 08/15] mm: Add unsafe_follow_pfn
Date: Thu, 29 Oct 2020 10:23:09 +0100
Message-ID: <CAKMK7uGVUf9RfTHKa8fpTUgGQ5iy+5toK+tQYp0TokKU=iM8pQ@mail.gmail.com> (raw)
In-Reply-To: <20201029085644.GA25658@infradead.org>

On Thu, Oct 29, 2020 at 9:56 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> > +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
> > +     unsigned long *pfn)
>
> The one tab indent here looks weird, normally tis would be two tabs
> or aligned aftetthe opening brace.
>
> > +{
> > +#ifdef CONFIG_STRICT_FOLLOW_PFN
> > +     pr_info("unsafe follow_pfn usage rejected, see CONFIG_STRICT_FOLLOW_PFN\n");
> > +     return -EINVAL;
> > +#else
> > +     WARN_ONCE(1, "unsafe follow_pfn usage\n");
> > +     add_taint(TAINT_USER, LOCKDEP_STILL_OK);
> > +
> > +     return follow_pfn(vma, address, pfn);
> > +#endif
>
> Woudn't this be a pretty good use case of "if (IS_ENABLED(...)))"?
>
> Also I'd expect the inverse polarity of the config option, that is
> a USAFE_FOLLOW_PFN option to enable to unsafe behavior.

Was just about to send out v5, will apply your suggestions for that
using IS_ENABLED.

Wrt negative or positive Kconfig, I was following STRICT_DEVMEM symbol
as precedence. But easy to invert if there's strong feeling the other
way round, I'm not attached to either.

> > +/**
> > + * unsafe_follow_pfn - look up PFN at a user virtual address
> > + * @vma: memory mapping
> > + * @address: user virtual address
> > + * @pfn: location to store found PFN
> > + *
> > + * Only IO mappings and raw PFN mappings are allowed.
> > + *
> > + * Returns zero and the pfn at @pfn on success, -ve otherwise.
> > + */
> > +int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
> > +     unsigned long *pfn)
> > +{
> > +     return follow_pfn(vma, address, pfn);
> > +}
> > +EXPORT_SYMBOL(unsafe_follow_pfn);
>
> Any reason this doesn't use the warn and disable logic?

I figured without an mmu there's not much guarantees anyway. But I
guess I can put it in here too for consistency.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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  parent reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 10:58 [PATCH v4 00/15] follow_pfn and other iomap races Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 01/15] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 02/15] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 03/15] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 04/15] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 05/15] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-26 22:15   ` Tomasz Figa
2020-10-27  8:05     ` Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 06/15] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-26 22:03   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 07/15] mm: Close race in generic_access_phys Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 08/15] mm: Add unsafe_follow_pfn Daniel Vetter
     [not found]   ` <20201029085644.GA25658@infradead.org>
2020-10-29  9:23     ` Daniel Vetter [this message]
2020-10-26 10:58 ` [PATCH v4 09/15] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-26 22:02   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 10/15] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 11/15] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 12/15] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 13/15] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 14/15] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 15/15] PCI: Revoke mappings like devmem Daniel Vetter
     [not found] ` <20201029085749.GB25658@infradead.org>
2020-10-29  9:25   ` [PATCH v4 00/15] follow_pfn and other iomap races Daniel Vetter
     [not found]     ` <20201029092800.GA494@infradead.org>
2020-10-29  9:38       ` Daniel Vetter

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