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, 57 insertions, 0 deletions

diff --git a/arch/mips/jazz/reset.c b/arch/mips/jazz/reset.c
new file mode 100644
index 000000000..052b01f5d
--- /dev/null
+++ b/arch/mips/jazz/reset.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Reset a Jazz machine.
+ *
+ * We don't trust the firmware so we do it the classic way by poking and
+ * stabbing at the keyboard controller ...
+ */
+#include <linux/jiffies.h>
+#include <asm/jazz.h>
+
+#define KBD_STAT_IBF		0x02	/* Keyboard input buffer full */
+
+static void jazz_write_output(unsigned char val)
+{
+	int status;
+
+	do {
+		status = jazz_kh->command;
+	} while (status & KBD_STAT_IBF);
+	jazz_kh->data = val;
+}
+
+static void jazz_write_command(unsigned char val)
+{
+	int status;
+
+	do {
+		status = jazz_kh->command;
+	} while (status & KBD_STAT_IBF);
+	jazz_kh->command = val;
+}
+
+static unsigned char jazz_read_status(void)
+{
+	return jazz_kh->command;
+}
+
+static inline void kb_wait(void)
+{
+	unsigned long start = jiffies;
+	unsigned long timeout = start + HZ/2;
+
+	do {
+		if (! (jazz_read_status() & 0x02))
+			return;
+	} while (time_before_eq(jiffies, timeout));
+}
+
+void jazz_machine_restart(char *command)
+{
+	while(1) {
+		kb_wait();
+		jazz_write_command(0xd1);
+		kb_wait();
+		jazz_write_output(0x00);
+	}
+}