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, 25 insertions, 0 deletions

diff --git a/arch/alpha/boot/bootloader.lds b/arch/alpha/boot/bootloader.lds
new file mode 100644
index 000000000..8cdff54c6
--- /dev/null
+++ b/arch/alpha/boot/bootloader.lds
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+OUTPUT_FORMAT("elf64-alpha")
+ENTRY(__start)
+printk = srm_printk;
+SECTIONS
+{
+  . = 0x20000000;
+  .text : { *(.text) }
+  _etext = .;
+  PROVIDE (etext = .);
+  .rodata : { *(.rodata) *(.rodata.*) }
+  .data : { *(.data) CONSTRUCTORS }
+  .got : { *(.got) }
+  .sdata : { *(.sdata) }
+  _edata = .;
+  PROVIDE (edata = .);
+  .sbss : { *(.sbss) *(.scommon) }
+  .bss : { *(.bss) *(COMMON) }
+  _end = . ;
+  PROVIDE (end = .);
+
+  .mdebug 0 : { *(.mdebug) }
+  .note 0 : { *(.note) }
+  .comment 0 : { *(.comment) }
+}