linux-kernel - [PATCH] async_pq: Remove VLA usage

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Message-Id: <20180503225716.154235-1-ksspiers@google.com>
Date:   Thu,  3 May 2018 15:57:16 -0700
From:   Kyle Spiers <ksspiers@...gle.com>
To:     dan.j.williams@...el.com
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        keescook@...omium.org, vinod.koul@...el.com, ray.jui@...adcom.com,
        anup.patel@...adcom.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kyle Spiers <ksspiers@...gle.com>
Subject: [PATCH] async_pq: Remove VLA usage

In the quest to remove VLAs from the kernel[1], this moves the
allocation of coefs and blocks from the stack to being kmalloc()ed.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Kyle Spiers <ksspiers@...gle.com>
---
 crypto/async_tx/async_pq.c  | 18 ++++++++++++++----
 crypto/async_tx/raid6test.c |  8 +++++++-
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index 56bd612927ab..af1912313a23 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
 	    (src_cnt <= dma_maxpq(device, 0) ||
 	     dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
 	    is_dma_pq_aligned(device, offset, 0, len)) {
-		struct dma_async_tx_descriptor *tx;
+		struct dma_async_tx_descriptor *tx = NULL;
 		enum dma_ctrl_flags dma_flags = 0;
-		unsigned char coefs[src_cnt];
+		unsigned char *coefs;
 		int i, j;
 
 		/* run the p+q asynchronously */
@@ -207,6 +207,9 @@ async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
 		 * sources and update the coefficients accordingly
 		 */
 		unmap->len = len;
+		coefs = kmalloc_array(src_cnt, sizeof(*coefs), GFP_KERNEL);
+		if (!coefs)
+			goto out;
 		for (i = 0, j = 0; i < src_cnt; i++) {
 			if (blocks[i] == NULL)
 				continue;
@@ -240,7 +243,9 @@ async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
 		}
 
 		tx = do_async_gen_syndrome(chan, coefs, j, unmap, dma_flags, submit);
+out:
 		dmaengine_unmap_put(unmap);
+		kfree(coefs);
 		return tx;
 	}
 
@@ -298,8 +303,8 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 {
 	struct dma_chan *chan = pq_val_chan(submit, blocks, disks, len);
 	struct dma_device *device = chan ? chan->device : NULL;
-	struct dma_async_tx_descriptor *tx;
-	unsigned char coefs[disks-2];
+	struct dma_async_tx_descriptor *tx = NULL;
+	unsigned char *coefs = NULL;
 	enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
 	struct dmaengine_unmap_data *unmap = NULL;
 
@@ -318,6 +323,9 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 			 __func__, disks, len);
 
 		unmap->len = len;
+		coefs = kmalloc_array(disks - 2, sizeof(*coefs), GFP_KERNEL);
+		if (!coefs)
+			goto out;
 		for (i = 0; i < disks-2; i++)
 			if (likely(blocks[i])) {
 				unmap->addr[j] = dma_map_page(dev, blocks[i],
@@ -423,6 +431,8 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 		async_tx_sync_epilog(submit);
 		tx = NULL;
 	}
+out:
+	kfree(coefs);
 	dmaengine_unmap_put(unmap);
 
 	return tx;
diff --git a/crypto/async_tx/raid6test.c b/crypto/async_tx/raid6test.c
index dad95f45b88f..ea036b531ef2 100644
--- a/crypto/async_tx/raid6test.c
+++ b/crypto/async_tx/raid6test.c
@@ -81,11 +81,16 @@ static void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, stru
 			init_async_submit(&submit, 0, NULL, NULL, NULL, addr_conv);
 			tx = async_gen_syndrome(ptrs, 0, disks, bytes, &submit);
 		} else {
-			struct page *blocks[disks];
+			struct page **blocks;
 			struct page *dest;
 			int count = 0;
 			int i;
 
+			blocks = kmalloc_array(disks, sizeof(*blocks),
+							GFP_KERNEL);
+			if (!blocks)
+				return;
+
 			/* data+Q failure.  Reconstruct data from P,
 			 * then rebuild syndrome
 			 */
@@ -101,6 +106,7 @@ static void raid6_dual_recov(int disks, size_t bytes, int faila, int failb, stru
 
 			init_async_submit(&submit, 0, tx, NULL, NULL, addr_conv);
 			tx = async_gen_syndrome(ptrs, 0, disks, bytes, &submit);
+			kfree(blocks);
 		}
 	} else {
 		if (failb == disks-2) {
-- 
2.17.0.441.gb46fe60e1d-goog