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, 61 insertions, 0 deletions

diff --git a/include/uapi/video/uvesafb.h b/include/uapi/video/uvesafb.h
new file mode 100644
index 000000000..a0d5c9213
--- /dev/null
+++ b/include/uapi/video/uvesafb.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_UVESAFB_H
+#define _UAPI_UVESAFB_H
+
+#include <linux/types.h>
+
+struct v86_regs {
+	__u32 ebx;
+	__u32 ecx;
+	__u32 edx;
+	__u32 esi;
+	__u32 edi;
+	__u32 ebp;
+	__u32 eax;
+	__u32 eip;
+	__u32 eflags;
+	__u32 esp;
+	__u16 cs;
+	__u16 ss;
+	__u16 es;
+	__u16 ds;
+	__u16 fs;
+	__u16 gs;
+};
+
+/* Task flags */
+#define TF_VBEIB	0x01
+#define TF_BUF_ESDI	0x02
+#define TF_BUF_ESBX	0x04
+#define TF_BUF_RET	0x08
+#define TF_EXIT		0x10
+
+struct uvesafb_task {
+	__u8 flags;
+	int buf_len;
+	struct v86_regs regs;
+};
+
+/* Constants for the capabilities field
+ * in vbe_ib */
+#define VBE_CAP_CAN_SWITCH_DAC	0x01
+#define VBE_CAP_VGACOMPAT	0x02
+
+/* The VBE Info Block */
+struct vbe_ib {
+	char  vbe_signature[4];
+	__u16 vbe_version;
+	__u32 oem_string_ptr;
+	__u32 capabilities;
+	__u32 mode_list_ptr;
+	__u16 total_memory;
+	__u16 oem_software_rev;
+	__u32 oem_vendor_name_ptr;
+	__u32 oem_product_name_ptr;
+	__u32 oem_product_rev_ptr;
+	__u8  reserved[222];
+	char  oem_data[256];
+	char  misc_data[512];
+} __attribute__ ((packed));
+
+#endif /* _UAPI_UVESAFB_H */