In the Linux kernel, the following vulnerability has been resolved:

spi: xilinx: use FIFO occupancy register to determine buffer size

The method the driver uses to determine the size of the FIFO has a
problem. What it currently does is this:
It stops the SPI hardware and writes to the TX FIFO register until TX
FIFO FULL asserts in the status register. But the hardware does not only
have the FIFO, it also has a shift register which can hold a byte. This
can be seen, when writing a byte to the FIFO (while the SPI hardware is
stopped,) the TX FIFO EMPTY is still empty. So, if we have a FIFO size
of 16 for example, the current method returns a 17.
This is a problem, at least when using the driver in irq mode. The same
size determined for the TX FIFO is also assumed for the RX FIFO. When a
SPI transaction wants to write the amount of the FIFO size or more
bytes, the following happens, for example with 16 bytes FIFO size:
The driver stops the SPI hardware and writes 17 bytes to the TX FIFO and
starts the SPI hardware and goes sleep.
The hardware then shifts out 17 bytes (FIFO + shift register) and
simultaneously reads bytes into the RX FIFO, but it only has 16 places,
so it looses one byte. Then TX FIFO empty asserts, wakes the driver
again, which has a fast path and reads 16 bytes from the RX FIFO, but
before reading the last 17th byte (which is lost) it does this:

	sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
	if (!(sr & XSPI_SR_RX_EMPTY_MASK)) {
		xilinx_spi_rx(xspi);
		rx_words--;
	}

It reads the status register and checks if the RX FIFO is not empty.
But it is empty in our case. So this check spins in a while loop
forever locking the driver.

This patch fixes the logic to determine the FIFO size.

https://git.kernel.org/stable/c/1c9246a199e19b2fd36e94feed60e55f27103a4f

https://git.kernel.org/stable/c/1fc6a6c0cc7796b0c1cf4eec3f0720f422f09273

https://git.kernel.org/stable/c/47f3b5365536e8c38f264824ab15fdb74454e066

https://git.kernel.org/stable/c/4ee65558a7fda463222f5edc631b6d7862218725

https://git.kernel.org/stable/c/d1944b71c18e7494756bff1a6f80c25be99eaecb

https://git.kernel.org/stable/c/d7ccd8736b67550eca746ed7fa39a36016ff114b

https://git.kernel.org/stable/c/dfab0d4698a642bab9b895e2e6d240838cfe2cc6

https://git.kernel.org/stable/c/e98f589d54068dfcc7da42d9b730e47b84e2991a

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