Subject: CVE-2022-48853: swiotlb: fix info leak with DMA_FROM_DEVICE

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

swiotlb: fix info leak with DMA_FROM_DEVICE

The problem I'm addressing was discovered by the LTP test covering
cve-2018-1000204.

A short description of what happens follows:
1) The test case issues a command code 00 (TEST UNIT READY) via the SG_IO
   interface with: dxfer_len == 524288, dxdfer_dir == SG_DXFER_FROM_DEV
   and a corresponding dxferp. The peculiar thing about this is that TUR
   is not reading from the device.
2) In sg_start_req() the invocation of blk_rq_map_user() effectively
   bounces the user-space buffer. As if the device was to transfer into
   it. Since commit a45b599ad808 ("scsi: sg: allocate with __GFP_ZERO in
   sg_build_indirect()") we make sure this first bounce buffer is
   allocated with GFP_ZERO.
3) For the rest of the story we keep ignoring that we have a TUR, so the
   device won't touch the buffer we prepare as if the we had a
   DMA_FROM_DEVICE type of situation. My setup uses a virtio-scsi device
   and the  buffer allocated by SG is mapped by the function
   virtqueue_add_split() which uses DMA_FROM_DEVICE for the "in" sgs (here
   scatter-gather and not scsi generics). This mapping involves bouncing
   via the swiotlb (we need swiotlb to do virtio in protected guest like
   s390 Secure Execution, or AMD SEV).
4) When the SCSI TUR is done, we first copy back the content of the second
   (that is swiotlb) bounce buffer (which most likely contains some
   previous IO data), to the first bounce buffer, which contains all
   zeros.  Then we copy back the content of the first bounce buffer to
   the user-space buffer.
5) The test case detects that the buffer, which it zero-initialized,
  ain't all zeros and fails.

One can argue that this is an swiotlb problem, because without swiotlb
we leak all zeros, and the swiotlb should be transparent in a sense that
it does not affect the outcome (if all other participants are well
behaved).

Copying the content of the original buffer into the swiotlb buffer is
the only way I can think of to make swiotlb transparent in such
scenarios. So let's do just that if in doubt, but allow the driver
to tell us that the whole mapped buffer is going to be overwritten,
in which case we can preserve the old behavior and avoid the performance
impact of the extra bounce.

The Linux kernel CVE team has assigned CVE-2022-48853 to this issue.

Affected and fixed versions
===========================

	Fixed in 4.9.320 with commit c132f2ba716b
	Fixed in 4.14.281 with commit 971e5dadffd0
	Fixed in 4.19.245 with commit 8d9ac1b6665c
	Fixed in 5.4.189 with commit 6bfc5377a210
	Fixed in 5.10.110 with commit d4d975e79210
	Fixed in 5.15.29 with commit 7403f4118ab9
	Fixed in 5.16.15 with commit 270475d6d241
	Fixed in 5.17 with commit ddbd89deb7d3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48853
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	Documentation/core-api/dma-attributes.rst
	include/linux/dma-mapping.h
	kernel/dma/swiotlb.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/c132f2ba716b5ee6b35f82226a6e5417d013d753
	https://git.kernel.org/stable/c/971e5dadffd02beba1063e7dd9c3a82de17cf534
	https://git.kernel.org/stable/c/8d9ac1b6665c73f23e963775f85d99679fd8e192
	https://git.kernel.org/stable/c/6bfc5377a210dbda2a237f16d94d1bd4f1335026
	https://git.kernel.org/stable/c/d4d975e7921079f877f828099bb8260af335508f
	https://git.kernel.org/stable/c/7403f4118ab94be837ab9d770507537a8057bc63
	https://git.kernel.org/stable/c/270475d6d2410ec66e971bf181afe1958dad565e
	https://git.kernel.org/stable/c/ddbd89deb7d32b1fbb879f48d68fda1a8ac58e8e