Revert swiotlb: rework fix info leak with DMA_FROM_DEVICE5.17-3

Bug: https://bugs.gentoo.org/835513

Signed-off-by: Mike Pagano <mpagano@gentoo.org>

2 files changed, 191 insertions, 0 deletions

diff --git a/0000_README b/0000_README
index 684989ae..19269be2 100644
--- a/0000_README
+++ b/0000_README
@@ -63,6 +63,10 @@ Patch:  2400_mt76-mt7921e-fix-possible-probe-failure-after-reboot.patch
 From:   https://patchwork.kernel.org/project/linux-wireless/patch/70e27cbc652cbdb78277b9c691a3a5ba02653afb.1641540175.git.objelf@gmail.com/
 Desc:   mt76: mt7921e: fix possible probe failure after reboot
 
+Patch:  2410_revert-swiotlb-rework-fix-info-leak-with-dma_from_device.patch
+From:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git
+Desc:   Revert swiotlb: rework fix info leak with DMA_FROM_DEVICE
+
 Patch:  2900_tmp513-Fix-build-issue-by-selecting-CONFIG_REG.patch
 From:   https://bugs.gentoo.org/710790
 Desc:   tmp513 requies REGMAP_I2C to build.  Select it by default in Kconfig. See bug #710790. Thanks to Phil Stracchino
diff --git a/2410_revert-swiotlb-rework-fix-info-leak-with-dma_from_device.patch b/2410_revert-swiotlb-rework-fix-info-leak-with-dma_from_device.patch
new file mode 100644
index 00000000..69476ab1
--- /dev/null
+++ b/2410_revert-swiotlb-rework-fix-info-leak-with-dma_from_device.patch
@@ -0,0 +1,187 @@
+From bddac7c1e02ba47f0570e494c9289acea3062cc1 Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Sat, 26 Mar 2022 10:42:04 -0700
+Subject: Revert "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Linus Torvalds <torvalds@linux-foundation.org>
+
+commit bddac7c1e02ba47f0570e494c9289acea3062cc1 upstream.
+
+This reverts commit aa6f8dcbab473f3a3c7454b74caa46d36cdc5d13.
+
+It turns out this breaks at least the ath9k wireless driver, and
+possibly others.
+
+What the ath9k driver does on packet receive is to set up the DMA
+transfer with:
+
+  int ath_rx_init(..)
+  ..
+                bf->bf_buf_addr = dma_map_single(sc->dev, skb->data,
+                                                 common->rx_bufsize,
+                                                 DMA_FROM_DEVICE);
+
+and then the receive logic (through ath_rx_tasklet()) will fetch
+incoming packets
+
+  static bool ath_edma_get_buffers(..)
+  ..
+        dma_sync_single_for_cpu(sc->dev, bf->bf_buf_addr,
+                                common->rx_bufsize, DMA_FROM_DEVICE);
+
+        ret = ath9k_hw_process_rxdesc_edma(ah, rs, skb->data);
+        if (ret == -EINPROGRESS) {
+                /*let device gain the buffer again*/
+                dma_sync_single_for_device(sc->dev, bf->bf_buf_addr,
+                                common->rx_bufsize, DMA_FROM_DEVICE);
+                return false;
+        }
+
+and it's worth noting how that first DMA sync:
+
+    dma_sync_single_for_cpu(..DMA_FROM_DEVICE);
+
+is there to make sure the CPU can read the DMA buffer (possibly by
+copying it from the bounce buffer area, or by doing some cache flush).
+The iommu correctly turns that into a "copy from bounce bufer" so that
+the driver can look at the state of the packets.
+
+In the meantime, the device may continue to write to the DMA buffer, but
+we at least have a snapshot of the state due to that first DMA sync.
+
+But that _second_ DMA sync:
+
+    dma_sync_single_for_device(..DMA_FROM_DEVICE);
+
+is telling the DMA mapping that the CPU wasn't interested in the area
+because the packet wasn't there.  In the case of a DMA bounce buffer,
+that is a no-op.
+
+Note how it's not a sync for the CPU (the "for_device()" part), and it's
+not a sync for data written by the CPU (the "DMA_FROM_DEVICE" part).
+
+Or rather, it _should_ be a no-op.  That's what commit aa6f8dcbab47
+broke: it made the code bounce the buffer unconditionally, and changed
+the DMA_FROM_DEVICE to just unconditionally and illogically be
+DMA_TO_DEVICE.
+
+[ Side note: purely within the confines of the swiotlb driver it wasn't
+  entirely illogical: The reason it did that odd DMA_FROM_DEVICE ->
+  DMA_TO_DEVICE conversion thing is because inside the swiotlb driver,
+  it uses just a swiotlb_bounce() helper that doesn't care about the
+  whole distinction of who the sync is for - only which direction to
+  bounce.
+
+  So it took the "sync for device" to mean that the CPU must have been
+  the one writing, and thought it meant DMA_TO_DEVICE. ]
+
+Also note how the commentary in that commit was wrong, probably due to
+that whole confusion, claiming that the commit makes the swiotlb code
+
+                                  "bounce unconditionally (that is, also
+    when dir == DMA_TO_DEVICE) in order do avoid synchronising back stale
+    data from the swiotlb buffer"
+
+which is nonsensical for two reasons:
+
+ - that "also when dir == DMA_TO_DEVICE" is nonsensical, as that was
+   exactly when it always did - and should do - the bounce.
+
+ - since this is a sync for the device (not for the CPU), we're clearly
+   fundamentally not coping back stale data from the bounce buffers at
+   all, because we'd be copying *to* the bounce buffers.
+
+So that commit was just very confused.  It confused the direction of the
+synchronization (to the device, not the cpu) with the direction of the
+DMA (from the device).
+
+Reported-and-bisected-by: Oleksandr Natalenko <oleksandr@natalenko.name>
+Reported-by: Olha Cherevyk <olha.cherevyk@gmail.com>
+Cc: Halil Pasic <pasic@linux.ibm.com>
+Cc: Christoph Hellwig <hch@lst.de>
+Cc: Kalle Valo <kvalo@kernel.org>
+Cc: Robin Murphy <robin.murphy@arm.com>
+Cc: Toke Høiland-Jørgensen <toke@toke.dk>
+Cc: Maxime Bizon <mbizon@freebox.fr>
+Cc: Johannes Berg <johannes@sipsolutions.net>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ Documentation/core-api/dma-attributes.rst |    8 ++++++++
+ include/linux/dma-mapping.h               |    8 ++++++++
+ kernel/dma/swiotlb.c                      |   23 ++++++++---------------
+ 3 files changed, 24 insertions(+), 15 deletions(-)
+
+--- a/Documentation/core-api/dma-attributes.rst
++++ b/Documentation/core-api/dma-attributes.rst
+@@ -130,3 +130,11 @@ accesses to DMA buffers in both privileg
+ subsystem that the buffer is fully accessible at the elevated privilege
+ level (and ideally inaccessible or at least read-only at the
+ lesser-privileged levels).
++
++DMA_ATTR_OVERWRITE
++------------------
++
++This is a hint to the DMA-mapping subsystem that the device is expected to
++overwrite the entire mapped size, thus the caller does not require any of the
++previous buffer contents to be preserved. This allows bounce-buffering
++implementations to optimise DMA_FROM_DEVICE transfers.
+--- a/include/linux/dma-mapping.h
++++ b/include/linux/dma-mapping.h
+@@ -62,6 +62,14 @@
+ #define DMA_ATTR_PRIVILEGED		(1UL << 9)
+ 
+ /*
++ * This is a hint to the DMA-mapping subsystem that the device is expected
++ * to overwrite the entire mapped size, thus the caller does not require any
++ * of the previous buffer contents to be preserved. This allows
++ * bounce-buffering implementations to optimise DMA_FROM_DEVICE transfers.
++ */
++#define DMA_ATTR_OVERWRITE		(1UL << 10)
++
++/*
+  * A dma_addr_t can hold any valid DMA or bus address for the platform.  It can
+  * be given to a device to use as a DMA source or target.  It is specific to a
+  * given device and there may be a translation between the CPU physical address
+--- a/kernel/dma/swiotlb.c
++++ b/kernel/dma/swiotlb.c
+@@ -627,14 +627,10 @@ phys_addr_t swiotlb_tbl_map_single(struc
+ 	for (i = 0; i < nr_slots(alloc_size + offset); i++)
+ 		mem->slots[index + i].orig_addr = slot_addr(orig_addr, i);
+ 	tlb_addr = slot_addr(mem->start, index) + offset;
+-	/*
+-	 * When dir == DMA_FROM_DEVICE we could omit the copy from the orig
+-	 * to the tlb buffer, if we knew for sure the device will
+-	 * overwirte the entire current content. But we don't. Thus
+-	 * unconditional bounce may prevent leaking swiotlb content (i.e.
+-	 * kernel memory) to user-space.
+-	 */
+-	swiotlb_bounce(dev, tlb_addr, mapping_size, DMA_TO_DEVICE);
++	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
++	    (!(attrs & DMA_ATTR_OVERWRITE) || dir == DMA_TO_DEVICE ||
++	    dir == DMA_BIDIRECTIONAL))
++		swiotlb_bounce(dev, tlb_addr, mapping_size, DMA_TO_DEVICE);
+ 	return tlb_addr;
+ }
+ 
+@@ -701,13 +697,10 @@ void swiotlb_tbl_unmap_single(struct dev
+ void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_addr,
+ 		size_t size, enum dma_data_direction dir)
+ {
+-	/*
+-	 * Unconditional bounce is necessary to avoid corruption on
+-	 * sync_*_for_cpu or dma_ummap_* when the device didn't overwrite
+-	 * the whole lengt of the bounce buffer.
+-	 */
+-	swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
+-	BUG_ON(!valid_dma_direction(dir));
++	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
++		swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
++	else
++		BUG_ON(dir != DMA_FROM_DEVICE);
+ }
+ 
+ void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,