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, 54 insertions, 0 deletions

diff --git a/scripts/coccinelle/misc/doubleinit.cocci b/scripts/coccinelle/misc/doubleinit.cocci
new file mode 100644
index 000000000..7dbfde3f4
--- /dev/null
+++ b/scripts/coccinelle/misc/doubleinit.cocci
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Find duplicate field initializations.  This has a high rate of false
+/// positives due to #ifdefs, which Coccinelle is not aware of in a structure
+/// initialization.
+///
+// Confidence: Low
+// Copyright: (C) 2010-2012 Nicolas Palix.
+// Copyright: (C) 2010-2012 Julia Lawall, INRIA/LIP6.
+// Copyright: (C) 2010-2012 Gilles Muller, INRIA/LiP6.
+// URL: https://coccinelle.gitlabpages.inria.fr/website
+// Comments: requires at least Coccinelle 0.2.4, lex or parse error otherwise
+// Options: --no-includes --include-headers
+
+virtual org
+virtual report
+
+@r@
+identifier I, s, fld;
+position p0,p;
+expression E;
+@@
+
+struct I s =@p0 { ..., .fld@p = E, ...};
+
+@s@
+identifier I, s, r.fld;
+position r.p0,p;
+expression E;
+@@
+
+struct I s =@p0 { ..., .fld@p = E, ...};
+
+@script:python depends on org@
+p0 << r.p0;
+fld << r.fld;
+ps << s.p;
+pr << r.p;
+@@
+
+if int(ps[0].line) < int(pr[0].line) or (int(ps[0].line) == int(pr[0].line) and int(ps[0].column) < int(pr[0].column)):
+  cocci.print_main(fld,p0)
+  cocci.print_secs("s",ps)
+  cocci.print_secs("r",pr)
+
+@script:python depends on report@
+p0 << r.p0;
+fld << r.fld;
+ps << s.p;
+pr << r.p;
+@@
+
+if int(ps[0].line) < int(pr[0].line) or (int(ps[0].line) == int(pr[0].line) and int(ps[0].column) < int(pr[0].column)):
+  msg = "%s: first occurrence line %s, second occurrence line %s" % (fld,ps[0].line,pr[0].line)
+  coccilib.report.print_report(p0[0],msg)