linux-kernel - [PATCH 13/13] vfio/type1: Mark follow

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Message-Id: <20201007164426.1812530-14-daniel.vetter@ffwll.ch>
Date:   Wed,  7 Oct 2020 18:44:26 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-media@...r.kernel.org,
        linux-s390@...r.kernel.org, Daniel Vetter <daniel.vetter@...ll.ch>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: [PATCH 13/13] vfio/type1: Mark follow_pfn as unsafe

The code seems to stuff these pfns into iommu pts (or something like
that, I didn't follow), but there's no mmu_notifier to ensure that
access is synchronized with pte updates.

Hence mark these as unsafe. This means that with
CONFIG_STRICT_FOLLOW_PFN, these will be rejected.

Real fix is to wire up an mmu_notifier ... somehow. Probably means any
invalidate is a fatal fault for this vfio device, but then this
shouldn't ever happen if userspace is reasonable.

Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Kees Cook <keescook@...omium.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: linux-mm@...ck.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-samsung-soc@...r.kernel.org
Cc: linux-media@...r.kernel.org
Cc: Alex Williamson <alex.williamson@...hat.com>
Cc: Cornelia Huck <cohuck@...hat.com>
Cc: kvm@...r.kernel.org
---
 drivers/vfio/vfio_iommu_type1.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 5fbf0c1f7433..a4d53f3d0a35 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -421,7 +421,7 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
 {
 	int ret;
 
-	ret = follow_pfn(vma, vaddr, pfn);
+	ret = unsafe_follow_pfn(vma, vaddr, pfn);
 	if (ret) {
 		bool unlocked = false;
 
@@ -435,7 +435,7 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
 		if (ret)
 			return ret;
 
-		ret = follow_pfn(vma, vaddr, pfn);
+		ret = unsafe_follow_pfn(vma, vaddr, pfn);
 	}
 
 	return ret;
-- 
2.28.0