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, 39 insertions, 0 deletions

diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
new file mode 100644
index 000000000..6b34ba193
--- /dev/null
+++ b/scripts/gcc-plugins/Kconfig
@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config HAVE_GCC_PLUGINS
+	bool
+	help
+	  An arch should select this symbol if it supports building with
+	  GCC plugins.
+
+menuconfig GCC_PLUGINS
+	bool "GCC plugins"
+	depends on HAVE_GCC_PLUGINS
+	depends on CC_IS_GCC
+	depends on $(success,test -e $(shell,$(CC) -print-file-name=plugin)/include/plugin-version.h)
+	default y
+	help
+	  GCC plugins are loadable modules that provide extra features to the
+	  compiler. They are useful for runtime instrumentation and static analysis.
+
+	  See Documentation/kbuild/gcc-plugins.rst for details.
+
+if GCC_PLUGINS
+
+config GCC_PLUGIN_LATENT_ENTROPY
+	bool "Generate some entropy during boot and runtime"
+	help
+	  By saying Y here the kernel will instrument some kernel code to
+	  extract some entropy from both original and artificially created
+	  program state.  This will help especially embedded systems where
+	  there is little 'natural' source of entropy normally.  The cost
+	  is some slowdown of the boot process (about 0.5%) and fork and
+	  irq processing.
+
+	  Note that entropy extracted this way is not cryptographically
+	  secure!
+
+	  This plugin was ported from grsecurity/PaX. More information at:
+	   * https://grsecurity.net/
+	   * https://pax.grsecurity.net/
+
+endif