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, 49 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-xdata b/Documentation/ABI/testing/sysfs-driver-xdata
new file mode 100644
index 000000000..f574e8e6d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-xdata
@@ -0,0 +1,49 @@
+What:		/sys/class/misc/drivers/dw-xdata-pcie.<device>/write
+Date:		April 2021
+KernelVersion:	5.13
+Contact:	Gustavo Pimentel <gustavo.pimentel@synopsys.com>
+Description:	Allows the user to enable the PCIe traffic generator which
+		will create write TLPs frames - from the Root Complex to the
+		Endpoint direction or to disable the PCIe traffic generator
+		in all directions.
+
+		Write y/1/on to enable, n/0/off to disable
+
+		Usage e.g.
+		 echo 1 > /sys/class/misc/dw-xdata-pcie.<device>/write
+		or
+		 echo 0 > /sys/class/misc/dw-xdata-pcie.<device>/write
+
+		The user can read the current PCIe link throughput generated
+		through this generator in MB/s.
+
+		Usage e.g.
+		 cat /sys/class/misc/dw-xdata-pcie.<device>/write
+		 204
+
+		The file is read and write.
+
+What:		/sys/class/misc/dw-xdata-pcie.<device>/read
+Date:		April 2021
+KernelVersion:	5.13
+Contact:	Gustavo Pimentel <gustavo.pimentel@synopsys.com>
+Description:	Allows the user to enable the PCIe traffic generator which
+		will create read TLPs frames - from the Endpoint to the Root
+		Complex direction or to disable the PCIe traffic generator
+                in all directions.
+
+		Write y/1/on to enable, n/0/off to disable
+
+		Usage e.g.
+		 echo 1 > /sys/class/misc/dw-xdata-pcie.<device>/read
+		or
+		 echo 0 > /sys/class/misc/dw-xdata-pcie.<device>/read
+
+		The user can read the current PCIe link throughput generated
+		through this generator in MB/s.
+
+		Usage e.g.
+		 cat /sys/class/misc/dw-xdata-pcie.<device>/read
+		 199
+
+		The file is read and write.