linux-kernel - [PATCH 5.15 380/667] dma-direct: dont over-decrypt memory

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Date:   Tue,  7 Jun 2022 19:00:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        David Rientjes <rientjes@...gle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 380/667] dma-direct: dont over-decrypt memory

From: Robin Murphy <robin.murphy@....com>

[ Upstream commit 4a37f3dd9a83186cb88d44808ab35b78375082c9 ]

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@....com>
Signed-off-by: Christoph Hellwig <hch@....de>
Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/dma/direct.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8e24455dd236..854d6df969de 100644
--- 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;
-- 
2.35.1