EDAC, thunderx: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], switch to
using a kmalloc-allocated buffer instead of stack space. This should be
fine since the existing routine is allocating memory too.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Jan Glauber <jglauber@cavium.com>
Cc: David Daney <david.daney@cavium.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/20180629184850.GA37464@beast
Link: https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com [1]
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/thunderx_edac.c

@@ -408,26 +408,29 @@ static ssize_t thunderx_lmc_inject_ecc_write(struct file *file,
 					     size_t count, loff_t *ppos)
 {
 	struct thunderx_lmc *lmc = file->private_data;
-
 	unsigned int cline_size = cache_line_size();
-
-	u8 tmp[cline_size];
+	u8 *tmp;
 	void __iomem *addr;
 	unsigned int offs, timeout = 100000;
 
 	atomic_set(&lmc->ecc_int, 0);
 
 	lmc->mem = alloc_pages_node(lmc->node, GFP_KERNEL, 0);
-
 	if (!lmc->mem)
 		return -ENOMEM;
 
+	tmp = kmalloc(cline_size, GFP_KERNEL);
+	if (!tmp) {
+		__free_pages(lmc->mem, 0);
+		return -ENOMEM;
+	}
+
 	addr = page_address(lmc->mem);
 
 	while (!atomic_read(&lmc->ecc_int) && timeout--) {
 		stop_machine(inject_ecc_fn, lmc, NULL);
 
-		for (offs = 0; offs < PAGE_SIZE; offs += sizeof(tmp)) {
+		for (offs = 0; offs < PAGE_SIZE; offs += cline_size) {
 			/*
 			 * Do a load from the previously rigged location
 			 * This should generate an error interrupt.
@@ -437,6 +440,7 @@ static ssize_t thunderx_lmc_inject_ecc_write(struct file *file,
 		}
 	}
 
+	kfree(tmp);
 	__free_pages(lmc->mem, 0);
 
 	return count;