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>

3 files changed, 45 insertions, 0 deletions

diff --git a/tools/pcmcia/.gitignore b/tools/pcmcia/.gitignore
new file mode 100644
index 000000000..94cb97b77
--- /dev/null
+++ b/tools/pcmcia/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+crc32hash
diff --git a/tools/pcmcia/Makefile b/tools/pcmcia/Makefile
new file mode 100644
index 000000000..eae24df1d
--- /dev/null
+++ b/tools/pcmcia/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+CC := $(CROSS_COMPILE)gcc
+CFLAGS := -I../../usr/include
+
+PROGS := crc32hash
+
+all: $(PROGS)
+
+clean:
+	rm -fr $(PROGS)
diff --git a/tools/pcmcia/crc32hash.c b/tools/pcmcia/crc32hash.c
new file mode 100644
index 000000000..1a18da9cb
--- /dev/null
+++ b/tools/pcmcia/crc32hash.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* crc32hash.c - derived from linux/lib/crc32.c, GNU GPL v2 */
+/* Usage example:
+$ ./crc32hash "Dual Speed"
+*/
+
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+static unsigned int crc32(unsigned char const *p, unsigned int len)
+{
+	int i;
+	unsigned int crc = 0;
+	while (len--) {
+		crc ^= *p++;
+		for (i = 0; i < 8; i++)
+			crc = (crc >> 1) ^ ((crc & 1) ? 0xedb88320 : 0);
+	}
+	return crc;
+}
+
+int main(int argc, char **argv) {
+	unsigned int result;
+	if (argc != 2) {
+		printf("no string passed as argument\n");
+		return -1;
+	}
+	result = crc32((unsigned char const *)argv[1], strlen(argv[1]));
+	printf("0x%x\n", result);
+	return 0;
+}