dma-direct: don't over-decrypt memory

The original x86 sev_alloc() only called set_memory_decrypted() on
memory returned by alloc_pages_node(), so the page order calculation
fell out of that logic. However, the common dma-direct code has several
potential allocators, not all of which are guaranteed to round up the
underlying allocation to a power-of-two size, so carrying over that
calculation for the encryption/decryption size was a mistake. Fix it by
rounding to a *number* of pages, rather than an order.

Until recently there was an even worse interaction with DMA_DIRECT_REMAP
where we could have ended up decrypting part of the next adjacent
vmalloc area, only averted by no architecture actually supporting both
configs at once. Don't ask how I found that one out...

Fixes: c10f07aa27da ("dma/direct: Handle force decryption for DMA coherent buffers in common code")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Rientjes <rientjes@google.com>

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 3e7f4aa..e978f36 100644 (file)
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -79,7 +79,7 @@ static int dma_set_decrypted(struct device *dev, void *vaddr, size_t size)
 {
        if (!force_dma_unencrypted(dev))
                return 0;
-       return set_memory_decrypted((unsigned long)vaddr, 1 << get_order(size));
+       return set_memory_decrypted((unsigned long)vaddr, PFN_UP(size));
 }
 
 static int dma_set_encrypted(struct device *dev, void *vaddr, size_t size)
@@ -88,7 +88,7 @@ static int dma_set_encrypted(struct device *dev, void *vaddr, size_t size)
 
        if (!force_dma_unencrypted(dev))
                return 0;
-       ret = set_memory_encrypted((unsigned long)vaddr, 1 << get_order(size));
+       ret = set_memory_encrypted((unsigned long)vaddr, PFN_UP(size));
        if (ret)
                pr_warn_ratelimited("leaking DMA memory that can't be re-encrypted\n");
        return ret;