linux-kernel - Re: [PATCH v1 15/16] iommu/tegra241-cmdqv: Add user-space use support

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Message-ID: <20250423231333.GN1648741@nvidia.com>
Date: Wed, 23 Apr 2025 20:13:33 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>, "corbet@....net" <corbet@....net>,
	"will@...nel.org" <will@...nel.org>,
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	"Liu, Yi L" <yi.l.liu@...el.com>,
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Subject: Re: [PATCH v1 15/16] iommu/tegra241-cmdqv: Add user-space use support

On Wed, Apr 23, 2025 at 11:31:29AM -0700, Nicolin Chen wrote:

> > It also needs to act like a mdev and lock down the part of the IOAS
> > that provides that memory so the pin can't be released and UAF things.
> 
> If I capture this correctly, the GPA->PA mapping is already done
> at the IOAS level for the S2 HWPT/domain, i.e. pages are already
> pinned. So we just need to a pair of for-driver APIs to validate
> the contiguity and refcount pages calling iopt_area_add_access().

Yes, adding an access is the key thing, the access will give you a
page list which you can validate, but it also provides a way to
synchronize if a hostile userspace does an unmap.

Jason