nvmem: rmem: make ->reg_read() straight forward code

memory_read_from_buffer() is a weird choice; it:
 - is made for iteration with ppos a pointer.
 - does futile error checking in our case.
 - does NOT ensure we read exactly N bytes.

Replace it by:
1. A check that (offset + bytes) lands inside the region and,
2. a plain memcpy().

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20241230143035.265518-5-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 9 deletions

diff --git a/drivers/nvmem/rmem.c b/drivers/nvmem/rmem.c
index 7f907c5a445e..0dc5c8237c75 100644
--- a/drivers/nvmem/rmem.c
+++ b/drivers/nvmem/rmem.c
@@ -21,10 +21,10 @@ static int rmem_read(void *context, unsigned int offset,
 		     void *val, size_t bytes)
 {
 	struct rmem *priv = context;
-	size_t available = priv->mem->size;
-	loff_t off = offset;
 	void *addr;
-	int count;
+
+	if ((phys_addr_t)offset + bytes > priv->mem->size)
+		return -EIO;
 
 	/*
 	 * Only map the reserved memory at this point to avoid potential rogue
@@ -36,20 +36,17 @@ static int rmem_read(void *context, unsigned int offset,
 	 * An alternative would be setting the memory as RO, set_memory_ro(),
 	 * but as of Dec 2020 this isn't possible on arm64.
 	 */
-	addr = memremap(priv->mem->base, available, MEMREMAP_WB);
+	addr = memremap(priv->mem->base, priv->mem->size, MEMREMAP_WB);
 	if (!addr) {
 		dev_err(priv->dev, "Failed to remap memory region\n");
 		return -ENOMEM;
 	}
 
-	count = memory_read_from_buffer(val, bytes, &off, addr, available);
+	memcpy(val, addr + offset, bytes);
 
 	memunmap(addr);
 
-	if (count < 0)
-		return count;
-
-	return count == bytes ? 0 : -EIO;
+	return 0;
 }
 
 static int rmem_probe(struct platform_device *pdev)