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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: DRI Development <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>
Cc: linux-s390@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
	"Jan Kara" <jack@suse.cz>, "Kees Cook" <keescook@chromium.org>,
	kvm@vger.kernel.org, "Jason Gunthorpe" <jgg@ziepe.ca>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	linux-mm@kvack.org, "Jérôme Glisse" <jglisse@redhat.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: [PATCH v4 08/15] mm: Add unsafe_follow_pfn
Date: Mon, 26 Oct 2020 11:58:11 +0100
Message-ID: <20201026105818.2585306-9-daniel.vetter@ffwll.ch> (raw)
In-Reply-To: <20201026105818.2585306-1-daniel.vetter@ffwll.ch>

Way back it was a reasonable assumptions that iomem mappings never
change the pfn range they point at. But this has changed:

- gpu drivers dynamically manage their memory nowadays, invalidating
ptes with unmap_mapping_range when buffers get moved

- contiguous dma allocations have moved from dedicated carvetouts to
cma regions. This means if we miss the unmap the pfn might contain
pagecache or anon memory (well anything allocated with GFP_MOVEABLE)

- even /dev/mem now invalidates mappings when the kernel requests that
iomem region when CONFIG_IO_STRICT_DEVMEM is set, see 3234ac664a87
("/dev/mem: Revoke mappings when a driver claims the region")

Accessing pfns obtained from ptes without holding all the locks is
therefore no longer a good idea.

Unfortunately there's some users where this is not fixable (like v4l
userptr of iomem mappings) or involves a pile of work (vfio type1
iommu). For now annotate these as unsafe and splat appropriately.

This patch adds an unsafe_follow_pfn, which later patches will then
roll out to all appropriate places.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: linux-mm@kvack.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 32 +++++++++++++++++++++++++++++++-
 mm/nommu.c         | 17 +++++++++++++++++
 security/Kconfig   | 13 +++++++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2a16631c1fda..ec8c90928fc9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1653,6 +1653,8 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
 		   pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
 int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 	unsigned long *pfn);
+int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address,
+		      unsigned long *pfn);
 int follow_phys(struct vm_area_struct *vma, unsigned long address,
 		unsigned int flags, unsigned long *prot, resource_size_t *phys);
 int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index 1b46eae3b703..9a2ec07ff20b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4788,7 +4788,12 @@ EXPORT_SYMBOL(follow_pte_pmd);
  * @address: user virtual address
  * @pfn: location to store found PFN
  *
- * Only IO mappings and raw PFN mappings are allowed.
+ * Only IO mappings and raw PFN mappings are allowed. Note that callers must
+ * ensure coherency with pte updates by using a &mmu_notifier to follow updates.
+ * If this is not feasible, or the access to the @pfn is only very short term,
+ * use follow_pte_pmd() instead and hold the pagetable lock for the duration of
+ * the access instead. Any caller not following these requirements must use
+ * unsafe_follow_pfn() instead.
  *
  * Return: zero and the pfn at @pfn on success, -ve otherwise.
  */
@@ -4811,6 +4816,31 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 }
 EXPORT_SYMBOL(follow_pfn);
 
+/**
+ * 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)
+{
+#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
+}
+EXPORT_SYMBOL(unsafe_follow_pfn);
+
 #ifdef CONFIG_HAVE_IOREMAP_PROT
 int follow_phys(struct vm_area_struct *vma,
 		unsigned long address, unsigned int flags,
diff --git a/mm/nommu.c b/mm/nommu.c
index 75a327149af1..3db2910f0d64 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -132,6 +132,23 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 }
 EXPORT_SYMBOL(follow_pfn);
 
+/**
+ * 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);
+
 LIST_HEAD(vmap_area_list);
 
 void vfree(const void *addr)
diff --git a/security/Kconfig b/security/Kconfig
index 7561f6f99f1d..48945402e103 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -230,6 +230,19 @@ config STATIC_USERMODEHELPER_PATH
 	  If you wish for all usermode helper programs to be disabled,
 	  specify an empty string here (i.e. "").
 
+config STRICT_FOLLOW_PFN
+	bool "Disable unsafe use of follow_pfn"
+	depends on MMU
+	help
+	  Some functionality in the kernel follows userspace mappings to iomem
+	  ranges in an unsafe matter. Examples include v4l userptr for zero-copy
+	  buffers sharing.
+
+	  If this option is switched on, such access is rejected. Only enable
+	  this option when you must run userspace which requires this.
+
+	  If in doubt, say Y.
+
 source "security/selinux/Kconfig"
 source "security/smack/Kconfig"
 source "security/tomoyo/Kconfig"
-- 
2.28.0

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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 ` Daniel Vetter [this message]
     [not found]   ` <20201029085644.GA25658@infradead.org>
2020-10-29  9:23     ` [PATCH v4 08/15] mm: Add unsafe_follow_pfn Daniel Vetter
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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