[tip: x86/mm] dma-mapping: Fix dma_pgprot() for unencrypted coherent pages

[tip-bot2 for Thomas Hellstrom]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     17c4a2ae15a7aaefe84bdb271952678c5c9cd8e1
Gitweb:        https://git.kernel.org/tip/17c4a2ae15a7aaefe84bdb271952678c5c9cd8e1
Author:        Thomas Hellstrom <thellstrom@xxxxxxxxxx>
AuthorDate:    Wed, 04 Mar 2020 12:45:27 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 17 Mar 2020 11:52:58 +01:00

dma-mapping: Fix dma_pgprot() for unencrypted coherent pages

When dma_mmap_coherent() sets up a mapping to unencrypted coherent memory
under SEV encryption and sometimes under SME encryption, it will actually
set up an encrypted mapping rather than an unencrypted, causing devices
that DMAs from that memory to read encrypted contents. Fix this.

When force_dma_unencrypted() returns true, the linear kernel map of the
coherent pages have had the encryption bit explicitly cleared and the
page content is unencrypted. Make sure that any additional PTEs we set
up to these pages also have the encryption bit cleared by having
dma_pgprot() return a protection with the encryption bit cleared in this
case.

Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://lkml.kernel.org/r/20200304114527.3636-3-thomas_os@xxxxxxxxxxxx
---
 kernel/dma/mapping.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 12ff766..98e3d87 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -154,6 +154,8 @@ EXPORT_SYMBOL(dma_get_sgtable_attrs);
  */
 pgprot_t dma_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs)
 {
+	if (force_dma_unencrypted(dev))
+		prot = pgprot_decrypted(prot);
 	if (dev_is_dma_coherent(dev) ||
 	    (IS_ENABLED(CONFIG_DMA_NONCOHERENT_CACHE_SYNC) &&
              (attrs & DMA_ATTR_NON_CONSISTENT)))