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, 42 insertions, 0 deletions

diff --git a/arch/powerpc/boot/stdlib.c b/arch/powerpc/boot/stdlib.c
new file mode 100644
index 000000000..868b019d6
--- /dev/null
+++ b/arch/powerpc/boot/stdlib.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * stdlib functions
+ *
+ * Author: Scott Wood <scottwood@freescale.com>
+ *
+ * Copyright (c) 2007 Freescale Semiconductor, Inc.
+ */
+
+#include "stdlib.h"
+
+/* Not currently supported: leading whitespace, sign, 0x prefix, zero base */
+unsigned long long int strtoull(const char *ptr, char **end, int base)
+{
+	unsigned long long ret = 0;
+
+	if (base > 36)
+		goto out;
+
+	while (*ptr) {
+		int digit;
+
+		if (*ptr >= '0' && *ptr <= '9' && *ptr < '0' + base)
+			digit = *ptr - '0';
+		else if (*ptr >= 'A' && *ptr < 'A' + base - 10)
+			digit = *ptr - 'A' + 10;
+		else if (*ptr >= 'a' && *ptr < 'a' + base - 10)
+			digit = *ptr - 'a' + 10;
+		else
+			break;
+
+		ret *= base;
+		ret += digit;
+		ptr++;
+	}
+
+out:
+	if (end)
+		*end = (char *)ptr;
+
+	return ret;
+}