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, 91 insertions, 0 deletions

diff --git a/scripts/coccinelle/misc/boolconv.cocci b/scripts/coccinelle/misc/boolconv.cocci
new file mode 100644
index 000000000..392994e93
--- /dev/null
+++ b/scripts/coccinelle/misc/boolconv.cocci
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Remove unneeded conversion to bool
+///
+//# Relational and logical operators evaluate to bool,
+//# explicit conversion is overly verbose and unneeded.
+//
+// Copyright: (C) 2016 Andrew F. Davis <afd@ti.com>
+
+virtual patch
+virtual context
+virtual org
+virtual report
+
+//----------------------------------------------------------
+//  For patch mode
+//----------------------------------------------------------
+
+@depends on patch@
+expression A, B;
+symbol true, false;
+@@
+
+(
+  A == B
+|
+  A != B
+|
+  A > B
+|
+  A < B
+|
+  A >= B
+|
+  A <= B
+|
+  A && B
+|
+  A || B
+)
+- ? true : false
+
+//----------------------------------------------------------
+//  For context mode
+//----------------------------------------------------------
+
+@r depends on !patch@
+expression A, B;
+symbol true, false;
+position p;
+@@
+
+(
+  A == B
+|
+  A != B
+|
+  A > B
+|
+  A < B
+|
+  A >= B
+|
+  A <= B
+|
+  A && B
+|
+  A || B
+)
+* ? true : false@p
+
+//----------------------------------------------------------
+//  For org mode
+//----------------------------------------------------------
+
+@script:python depends on r&&org@
+p << r.p;
+@@
+
+msg = "WARNING: conversion to bool not needed here"
+coccilib.org.print_todo(p[0], msg)
+
+//----------------------------------------------------------
+//  For report mode
+//----------------------------------------------------------
+
+@script:python depends on r&&report@
+p << r.p;
+@@
+
+msg = "WARNING: conversion to bool not needed here"
+coccilib.report.print_report(p[0], msg)