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, 32 insertions, 0 deletions

diff --git a/scripts/ssl-common.h b/scripts/ssl-common.h
new file mode 100644
index 000000000..2db0e1811
--- /dev/null
+++ b/scripts/ssl-common.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/*
+ * SSL helper functions shared by sign-file and extract-cert.
+ */
+
+static void drain_openssl_errors(int l, int silent)
+{
+	const char *file;
+	char buf[120];
+	int e, line;
+
+	if (ERR_peek_error() == 0)
+		return;
+	if (!silent)
+		fprintf(stderr, "At main.c:%d:\n", l);
+
+	while ((e = ERR_peek_error_line(&file, &line))) {
+		ERR_error_string(e, buf);
+		if (!silent)
+			fprintf(stderr, "- SSL %s: %s:%d\n", buf, file, line);
+		ERR_get_error();
+	}
+}
+
+#define ERR(cond, fmt, ...)				\
+	do {						\
+		bool __cond = (cond);			\
+		drain_openssl_errors(__LINE__, 0);	\
+		if (__cond) {				\
+			errx(1, fmt, ## __VA_ARGS__);	\
+		}					\
+	} while (0)