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, 59 insertions, 0 deletions

diff --git a/scripts/coccinelle/tests/doubletest.cocci b/scripts/coccinelle/tests/doubletest.cocci
new file mode 100644
index 000000000..c3d94c319
--- /dev/null
+++ b/scripts/coccinelle/tests/doubletest.cocci
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Find &&/|| operations that include the same argument more than once
+//# A common source of false positives is when the expression, or
+//# another expresssion in the same && or || operation, performs a
+//# side effect.
+///
+// Confidence: Moderate
+// Copyright: (C) 2010 Nicolas Palix, DIKU.
+// Copyright: (C) 2010 Julia Lawall, DIKU.
+// Copyright: (C) 2010 Gilles Muller, INRIA/LiP6.
+// URL: https://coccinelle.gitlabpages.inria.fr/website
+// Comments:
+// Options: --no-includes --include-headers
+
+virtual context
+virtual org
+virtual report
+
+@r expression@
+expression E;
+position p;
+@@
+
+(
+ E@p || ... || E
+|
+ E@p && ... && E
+)
+
+@bad@
+expression r.E,e1,e2,fn;
+position r.p;
+assignment operator op;
+@@
+
+(
+E@p
+&
+ <+... \(fn(...)\|e1 op e2\|e1++\|e1--\|++e1\|--e1\) ...+>
+)
+
+@depends on context && !bad@
+expression r.E;
+position r.p;
+@@
+
+*E@p
+
+@script:python depends on org && !bad@
+p << r.p;
+@@
+
+cocci.print_main("duplicated argument to && or ||",p)
+
+@script:python depends on report && !bad@
+p << r.p;
+@@
+
+coccilib.report.print_report(p[0],"duplicated argument to && or ||")