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, 70 insertions, 0 deletions

diff --git a/include/asm-generic/bitops/atomic.h b/include/asm-generic/bitops/atomic.h
new file mode 100644
index 000000000..e076e079f
--- /dev/null
+++ b/include/asm-generic/bitops/atomic.h
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_BITOPS_ATOMIC_H_
+#define _ASM_GENERIC_BITOPS_ATOMIC_H_
+
+#include <linux/atomic.h>
+#include <linux/compiler.h>
+#include <asm/barrier.h>
+
+/*
+ * Implementation of atomic bitops using atomic-fetch ops.
+ * See Documentation/atomic_bitops.txt for details.
+ */
+
+static __always_inline void
+arch_set_bit(unsigned int nr, volatile unsigned long *p)
+{
+	p += BIT_WORD(nr);
+	raw_atomic_long_or(BIT_MASK(nr), (atomic_long_t *)p);
+}
+
+static __always_inline void
+arch_clear_bit(unsigned int nr, volatile unsigned long *p)
+{
+	p += BIT_WORD(nr);
+	raw_atomic_long_andnot(BIT_MASK(nr), (atomic_long_t *)p);
+}
+
+static __always_inline void
+arch_change_bit(unsigned int nr, volatile unsigned long *p)
+{
+	p += BIT_WORD(nr);
+	raw_atomic_long_xor(BIT_MASK(nr), (atomic_long_t *)p);
+}
+
+static __always_inline int
+arch_test_and_set_bit(unsigned int nr, volatile unsigned long *p)
+{
+	long old;
+	unsigned long mask = BIT_MASK(nr);
+
+	p += BIT_WORD(nr);
+	old = raw_atomic_long_fetch_or(mask, (atomic_long_t *)p);
+	return !!(old & mask);
+}
+
+static __always_inline int
+arch_test_and_clear_bit(unsigned int nr, volatile unsigned long *p)
+{
+	long old;
+	unsigned long mask = BIT_MASK(nr);
+
+	p += BIT_WORD(nr);
+	old = raw_atomic_long_fetch_andnot(mask, (atomic_long_t *)p);
+	return !!(old & mask);
+}
+
+static __always_inline int
+arch_test_and_change_bit(unsigned int nr, volatile unsigned long *p)
+{
+	long old;
+	unsigned long mask = BIT_MASK(nr);
+
+	p += BIT_WORD(nr);
+	old = raw_atomic_long_fetch_xor(mask, (atomic_long_t *)p);
+	return !!(old & mask);
+}
+
+#include <asm-generic/bitops/instrumented-atomic.h>
+
+#endif /* _ASM_GENERIC_BITOPS_ATOMIC_H */