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, 19 insertions, 0 deletions

diff --git a/scripts/kconfig/preprocess.h b/scripts/kconfig/preprocess.h
new file mode 100644
index 000000000..a7e4a5506
--- /dev/null
+++ b/scripts/kconfig/preprocess.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef PREPROCESS_H
+#define PREPROCESS_H
+
+enum variable_flavor {
+	VAR_SIMPLE,
+	VAR_RECURSIVE,
+	VAR_APPEND,
+};
+
+struct gstr;
+void env_write_dep(struct gstr *gs);
+void variable_add(const char *name, const char *value,
+		  enum variable_flavor flavor);
+void variable_all_del(void);
+char *expand_dollar(const char **str);
+char *expand_one_token(const char **str);
+
+#endif /* PREPROCESS_H */