From: Lukas Wunner lukas@wunner.de
commit 13817d466eb8713a1ffd254f537402f091d48444 upstream.
Commit 571e31fa60b3 ("spi: bcm2835: Cache CS register value for ->prepare_message()") limited the number of slaves to 3 at compile-time. The limitation was necessitated by a statically-sized array prepare_cs[] in the driver private data which contains a per-slave register value.
The commit sought to enforce the limitation at run-time by setting the controller's num_chipselect to 3: Slaves with a higher chipselect are rejected by spi_add_device().
However the commit neglected that num_chipselect only limits the number of *native* chipselects. If GPIO chipselects are specified in the device tree for more than 3 slaves, num_chipselect is silently raised by of_spi_get_gpio_numbers() and the result are out-of-bounds accesses to the statically-sized array prepare_cs[].
As a bandaid fix which is backportable to stable, raise the number of allowed slaves to 24 (which "ought to be enough for anybody"), enforce the limitation on slave ->setup and revert num_chipselect to 3 (which is the number of native chipselects supported by the controller). An upcoming for-next commit will allow an arbitrary number of slaves.
Fixes: 571e31fa60b3 ("spi: bcm2835: Cache CS register value for ->prepare_message()") Reported-by: Joe Burmeister joe.burmeister@devtank.co.uk Signed-off-by: Lukas Wunner lukas@wunner.de Cc: stable@vger.kernel.org # v5.4+ Cc: Phil Elwell phil@raspberrypi.com Link: https://lore.kernel.org/r/75854affc1923309fde05e47494263bde73e5592.162170321... Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/spi/spi-bcm2835.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
--- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -68,7 +68,7 @@ #define BCM2835_SPI_FIFO_SIZE 64 #define BCM2835_SPI_FIFO_SIZE_3_4 48 #define BCM2835_SPI_DMA_MIN_LENGTH 96 -#define BCM2835_SPI_NUM_CS 4 /* raise as necessary */ +#define BCM2835_SPI_NUM_CS 24 /* raise as necessary */ #define BCM2835_SPI_MODE_BITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \ | SPI_NO_CS | SPI_3WIRE)
@@ -1195,6 +1195,12 @@ static int bcm2835_spi_setup(struct spi_ struct gpio_chip *chip; u32 cs;
+ if (spi->chip_select >= BCM2835_SPI_NUM_CS) { + dev_err(&spi->dev, "only %d chip-selects supported\n", + BCM2835_SPI_NUM_CS - 1); + return -EINVAL; + } + /* * Precalculate SPI slave's CS register value for ->prepare_message(): * The driver always uses software-controlled GPIO chip select, hence @@ -1288,7 +1294,7 @@ static int bcm2835_spi_probe(struct plat ctlr->use_gpio_descriptors = true; ctlr->mode_bits = BCM2835_SPI_MODE_BITS; ctlr->bits_per_word_mask = SPI_BPW_MASK(8); - ctlr->num_chipselect = BCM2835_SPI_NUM_CS; + ctlr->num_chipselect = 3; ctlr->setup = bcm2835_spi_setup; ctlr->transfer_one = bcm2835_spi_transfer_one; ctlr->handle_err = bcm2835_spi_handle_err;