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, 166 insertions, 0 deletions

diff --git a/lib/sys_info.c b/lib/sys_info.c
new file mode 100644
index 000000000..f32a06ec9
--- /dev/null
+++ b/lib/sys_info.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/array_size.h>
+#include <linux/bitops.h>
+#include <linux/cleanup.h>
+#include <linux/console.h>
+#include <linux/log2.h>
+#include <linux/kernel.h>
+#include <linux/ftrace.h>
+#include <linux/nmi.h>
+#include <linux/sched/debug.h>
+#include <linux/string.h>
+#include <linux/sysctl.h>
+
+#include <linux/sys_info.h>
+
+static const char * const si_names[] = {
+	[ilog2(SYS_INFO_TASKS)]			= "tasks",
+	[ilog2(SYS_INFO_MEM)]			= "mem",
+	[ilog2(SYS_INFO_TIMERS)]		= "timers",
+	[ilog2(SYS_INFO_LOCKS)]			= "locks",
+	[ilog2(SYS_INFO_FTRACE)]		= "ftrace",
+	[ilog2(SYS_INFO_PANIC_CONSOLE_REPLAY)]	= "",
+	[ilog2(SYS_INFO_ALL_BT)]		= "all_bt",
+	[ilog2(SYS_INFO_BLOCKED_TASKS)]		= "blocked_tasks",
+};
+
+/*
+ * Default kernel sys_info mask.
+ * If a kernel module calls sys_info() with "parameter == 0", then
+ * this mask will be used.
+ */
+static unsigned long kernel_si_mask;
+
+/* Expecting string like "xxx_sys_info=tasks,mem,timers,locks,ftrace,..." */
+unsigned long sys_info_parse_param(char *str)
+{
+	unsigned long si_bits = 0;
+	char *s, *name;
+	int i;
+
+	s = str;
+	while ((name = strsep(&s, ",")) && *name) {
+		i = match_string(si_names, ARRAY_SIZE(si_names), name);
+		if (i >= 0)
+			__set_bit(i, &si_bits);
+	}
+
+	return si_bits;
+}
+
+#ifdef CONFIG_SYSCTL
+
+static int sys_info_write_handler(const struct ctl_table *table,
+				  void *buffer, size_t *lenp, loff_t *ppos,
+				  unsigned long *si_bits_global)
+{
+	unsigned long si_bits;
+	int ret;
+
+	ret = proc_dostring(table, 1, buffer, lenp, ppos);
+	if (ret)
+		return ret;
+
+	si_bits = sys_info_parse_param(table->data);
+
+	/* The access to the global value is not synchronized. */
+	WRITE_ONCE(*si_bits_global, si_bits);
+
+	return 0;
+}
+
+static int sys_info_read_handler(const struct ctl_table *table,
+				 void *buffer, size_t *lenp, loff_t *ppos,
+				 unsigned long *si_bits_global)
+{
+	unsigned long si_bits;
+	unsigned int len = 0;
+	char *delim = "";
+	unsigned int i;
+
+	/* The access to the global value is not synchronized. */
+	si_bits = READ_ONCE(*si_bits_global);
+
+	for_each_set_bit(i, &si_bits, ARRAY_SIZE(si_names)) {
+		if (*si_names[i]) {
+			len += scnprintf(table->data + len, table->maxlen - len,
+					 "%s%s", delim, si_names[i]);
+			delim = ",";
+		}
+	}
+
+	return proc_dostring(table, 0, buffer, lenp, ppos);
+}
+
+int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
+					  void *buffer, size_t *lenp,
+					  loff_t *ppos)
+{
+	struct ctl_table table;
+	unsigned int i;
+	size_t maxlen;
+
+	maxlen = 0;
+	for (i = 0; i < ARRAY_SIZE(si_names); i++)
+		maxlen += strlen(si_names[i]) + 1;
+
+	char *names __free(kfree) = kzalloc(maxlen, GFP_KERNEL);
+	if (!names)
+		return -ENOMEM;
+
+	table = *ro_table;
+	table.data = names;
+	table.maxlen = maxlen;
+
+	if (write)
+		return sys_info_write_handler(&table, buffer, lenp, ppos, ro_table->data);
+	else
+		return sys_info_read_handler(&table, buffer, lenp, ppos, ro_table->data);
+}
+
+static const struct ctl_table sys_info_sysctls[] = {
+	{
+		.procname	= "kernel_sys_info",
+		.data		= &kernel_si_mask,
+		.maxlen         = sizeof(kernel_si_mask),
+		.mode		= 0644,
+		.proc_handler	= sysctl_sys_info_handler,
+	},
+};
+
+static int __init sys_info_sysctl_init(void)
+{
+	register_sysctl_init("kernel", sys_info_sysctls);
+	return 0;
+}
+subsys_initcall(sys_info_sysctl_init);
+#endif
+
+static void __sys_info(unsigned long si_mask)
+{
+	if (si_mask & SYS_INFO_TASKS)
+		show_state();
+
+	if (si_mask & SYS_INFO_MEM)
+		show_mem();
+
+	if (si_mask & SYS_INFO_TIMERS)
+		sysrq_timer_list_show();
+
+	if (si_mask & SYS_INFO_LOCKS)
+		debug_show_all_locks();
+
+	if (si_mask & SYS_INFO_FTRACE)
+		ftrace_dump(DUMP_ALL);
+
+	if (si_mask & SYS_INFO_ALL_BT)
+		trigger_all_cpu_backtrace();
+
+	if (si_mask & SYS_INFO_BLOCKED_TASKS)
+		show_state_filter(TASK_UNINTERRUPTIBLE);
+}
+
+void sys_info(unsigned long si_mask)
+{
+	__sys_info(si_mask ? : kernel_si_mask);
+}