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, 52 insertions, 0 deletions

diff --git a/Documentation/networking/dctcp.rst b/Documentation/networking/dctcp.rst
new file mode 100644
index 000000000..4cc8bb2da
--- /dev/null
+++ b/Documentation/networking/dctcp.rst
@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================
+DCTCP (DataCenter TCP)
+======================
+
+DCTCP is an enhancement to the TCP congestion control algorithm for data
+center networks and leverages Explicit Congestion Notification (ECN) in
+the data center network to provide multi-bit feedback to the end hosts.
+
+To enable it on end hosts::
+
+  sysctl -w net.ipv4.tcp_congestion_control=dctcp
+  sysctl -w net.ipv4.tcp_ecn_fallback=0 (optional)
+
+All switches in the data center network running DCTCP must support ECN
+marking and be configured for marking when reaching defined switch buffer
+thresholds. The default ECN marking threshold heuristic for DCTCP on
+switches is 20 packets (30KB) at 1Gbps, and 65 packets (~100KB) at 10Gbps,
+but might need further careful tweaking.
+
+For more details, see below documents:
+
+Paper:
+
+The algorithm is further described in detail in the following two
+SIGCOMM/SIGMETRICS papers:
+
+ i) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,
+    Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:
+
+      "Data Center TCP (DCTCP)", Data Center Networks session"
+
+      Proc. ACM SIGCOMM, New Delhi, 2010.
+
+    http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
+    http://www.sigcomm.org/ccr/papers/2010/October/1851275.1851192
+
+ii) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:
+
+      "Analysis of DCTCP: Stability, Convergence, and Fairness"
+      Proc. ACM SIGMETRICS, San Jose, 2011.
+
+    http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf
+
+IETF informational draft:
+
+  http://tools.ietf.org/html/draft-bensley-tcpm-dctcp-00
+
+DCTCP site:
+
+  http://simula.stanford.edu/~alizade/Site/DCTCP.html