openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-wilco-ec b/Documentation/ABI/testing/debugfs-wilco-ec
new file mode 100644
index 000000000..682e3c09e
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-wilco-ec
@@ -0,0 +1,45 @@
+What:		/sys/kernel/debug/wilco_ec/h1_gpio
+Date:		April 2019
+KernelVersion:	5.2
+Description:
+		As part of Chrome OS's FAFT (Fully Automated Firmware Testing)
+		tests, we need to ensure that the H1 chip is properly setting
+		some GPIO lines. The h1_gpio attribute exposes the state
+		of the lines:
+		- ENTRY_TO_FACT_MODE in BIT(0)
+		- SPI_CHROME_SEL in BIT(1)
+
+		Output will formatted with "0x%02x\n".
+
+What:		/sys/kernel/debug/wilco_ec/raw
+Date:		January 2019
+KernelVersion:	5.1
+Description:
+		Write and read raw mailbox commands to the EC.
+
+		You can write a hexadecimal sentence to raw, and that series of
+		bytes will be sent to the EC. Then, you can read the bytes of
+		response by reading from raw.
+
+		For writing, bytes 0-1 indicate the message type, one of enum
+		wilco_ec_msg_type. Byte 2+ consist of the data passed in the
+		request, starting at MBOX[0]. At least three bytes are required
+		for writing, two for the type and at least a single byte of
+		data.
+
+		Example::
+
+		    // Request EC info type 3 (EC firmware build date)
+		    // Corresponds with sending type 0x00f0 with
+		    // MBOX = [38, 00, 03, 00]
+		    $ echo 00 f0 38 00 03 00 > /sys/kernel/debug/wilco_ec/raw
+		    // View the result. The decoded ASCII result "12/21/18" is
+		    // included after the raw hex.
+		    // Corresponds with MBOX = [00, 00, 31, 32, 2f, 32, 31, 38, ...]
+		    $ cat /sys/kernel/debug/wilco_ec/raw
+		    00 00 31 32 2f 32 31 2f 31 38 00 38 00 01 00 2f 00  ..12/21/18.8...
+
+		Note that the first 16 bytes of the received MBOX[] will be
+		printed, even if some of the data is junk, and skipping bytes
+		17 to 32. It is up to you to know how many of the first bytes of
+		data are the actual response.