[PATCH] mtd: spi-nor: fix DMA unsafe buffer issue in spi_nor_read_sfdp()

Cyrille Pitchen
2017-09-07T00:11:02Z

spi_nor_read_sfdp() calls nor->read() to read the SFDP data.
When the m25p80 driver is used (pretty common case), nor->read() is then
implemented by the m25p80_read() function, which is likely to initialize a
'struct spi_transfer' from its buf argument before appending this
structure inside the 'struct spi_message' argument of spi_sync().

Besides the SPI sub-system states that both .tx_buf and .rx_buf members of
'struct spi_transfer' must point into dma-safe memory. However, two of the
three calls of spi_nor_read_sfdp() were given pointers to stack allocated
memory as buf argument, hence not in a dma-safe area.
Hopefully, the third and last call of spi_nor_read_sfdp() was already
given a kmalloc'ed buffer argument, hence dma-safe.

So this patch fixes this issue by introducing a
spi_nor_read_sfdp_dma_unsafe() function which simply wraps the existing
spi_nor_read_sfdp() function and uses some kmalloc'ed memory as a bounce
buffer.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>
---

Compiled but not tested yet!

drivers/mtd/spi-nor/spi-nor.c | 36 +++++++++++++++++++++++++++++++++---
1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index cf1d4a15e10a..05254dd6a4a0 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1784,7 +1784,7 @@ spi_nor_set_pp_settings(struct spi_nor_pp_command *pp,
* @nor: pointer to a 'struct spi_nor'
* @addr: offset in the SFDP area to start reading data from
* @len: number of bytes to read
- * @buf: buffer where the SFDP data are copied into
+ * @buf: buffer where the SFDP data are copied into (dma-safe memory)
*
* Whatever the actual numbers of bytes for address and dummy cycles are
* for (Fast) Read commands, the Read SFDP (5Ah) instruction is always
@@ -1829,6 +1829,36 @@ static int spi_nor_read_sfdp(struct spi_nor *nor, u32 addr,
return ret;
}

+/**
+ * spi_nor_read_sfdp_dma_unsafe() - read Serial Flash Discoverable Parameters.
+ * @nor: pointer to a 'struct spi_nor'
+ * @addr: offset in the SFDP area to start reading data from
+ * @len: number of bytes to read
+ * @buf: buffer where the SFDP data are copied into
+ *
+ * Wrap spi_nor_read_sfdp() using a kmalloc'ed bounce buffer as @buf is now not
+ * guaranteed to be dma-safe.
+ *
+ * Return: -ENOMEM if kmalloc() fails, the return code of spi_nor_read_sfdp()
+ * otherwise.
+ */
+static int spi_nor_read_sfdp_dma_unsafe(struct spi_nor *nor, u32 addr,
+ size_t len, void *buf)
+{
+ void *dma_safe_buf;
+ int ret;
+
+ dma_safe_buf = kmalloc(len, GFP_KERNEL);
+ if (!dma_safe_buf)
+ return -ENOMEM;
+
+ ret = spi_nor_read_sfdp(nor, addr, len, dma_safe_buf);
+ memcpy(buf, dma_safe_buf, len);
+ kfree(dma_safe_buf);
+
+ return ret;
+}
+
struct sfdp_parameter_header {
u8 id_lsb;
u8 minor;
@@ -2101,7 +2131,7 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
bfpt_header->length * sizeof(u32));
addr = SFDP_PARAM_HEADER_PTP(bfpt_header);
memset(&bfpt, 0, sizeof(bfpt));
- err = spi_nor_read_sfdp(nor, addr, len, &bfpt);
+ err = spi_nor_read_sfdp_dma_unsafe(nor, addr, len, &bfpt);
if (err < 0)
return err;

@@ -2243,7 +2273,7 @@ static int spi_nor_parse_sfdp(struct spi_nor *nor,
int i, err;

/* Get the SFDP header. */
- err = spi_nor_read_sfdp(nor, 0, sizeof(header), &header);
+ err = spi_nor_read_sfdp_dma_unsafe(nor, 0, sizeof(header), &header);
if (err < 0)
return err;

--
2.11.0