Re: [PATCH v3 2/2] dma-mapping: Fix dma_pgprot() for unencrypted coherent pages

[Tom Lendacky <thomas.lendacky@amd.com>]

On 3/4/20 5:45 AM, Thomas Hellström (VMware) wrote:
> From: Thomas Hellstrom <thellstrom@vmware.com>
> 
> 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.
> 
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

Acked-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>  kernel/dma/mapping.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 12ff766ec1fa..98e3d873792e 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)))
>