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, 73 insertions, 0 deletions

diff --git a/Documentation/process/8.Conclusion.rst b/Documentation/process/8.Conclusion.rst
new file mode 100644
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+++ b/Documentation/process/8.Conclusion.rst
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+.. _development_conclusion:
+
+For more information
+====================
+
+There are numerous sources of information on Linux kernel development and
+related topics.  First among those will always be the Documentation
+directory found in the kernel source distribution.  Start with the
+top-level :ref:`process/howto.rst <process_howto>`; also read
+:ref:`process/submitting-patches.rst <submittingpatches>`. Many internal
+kernel APIs are documented using the kerneldoc mechanism; "make htmldocs"
+or "make pdfdocs" can be used to generate those documents in HTML or PDF
+format (though the version of TeX shipped by some distributions runs into
+internal limits and fails to process the documents properly).
+
+Various web sites discuss kernel development at all levels of detail.  Your
+author would like to humbly suggest https://lwn.net/ as a source;
+information on many specific kernel topics can be found via the LWN kernel
+index at:
+
+	https://lwn.net/Kernel/Index/
+
+Beyond that, a valuable resource for kernel developers is:
+
+	https://kernelnewbies.org/
+
+And, of course, one should not forget https://kernel.org/, the definitive
+location for kernel release information.
+
+There are a number of books on kernel development:
+
+	Linux Device Drivers, 3rd Edition (Jonathan Corbet, Alessandro
+	Rubini, and Greg Kroah-Hartman).  Online at
+	https://lwn.net/Kernel/LDD3/.
+
+	Linux Kernel Development (Robert Love).
+
+	Understanding the Linux Kernel (Daniel Bovet and Marco Cesati).
+
+All of these books suffer from a common fault, though: they tend to be
+somewhat obsolete by the time they hit the shelves, and they have been on
+the shelves for a while now.  Still, there is quite a bit of good
+information to be found there.
+
+Documentation for git can be found at:
+
+	https://www.kernel.org/pub/software/scm/git/docs/
+
+	https://www.kernel.org/pub/software/scm/git/docs/user-manual.html
+
+
+Conclusion
+==========
+
+Congratulations to anybody who has made it through this long-winded
+document.  Hopefully it has provided a helpful understanding of how the
+Linux kernel is developed and how you can participate in that process.
+
+In the end, it's the participation that matters.  Any open source software
+project is no more than the sum of what its contributors put into it.  The
+Linux kernel has progressed as quickly and as well as it has because it has
+been helped by an impressively large group of developers, all of whom are
+working to make it better.  The kernel is a premier example of what can be
+done when thousands of people work together toward a common goal.
+
+The kernel can always benefit from a larger developer base, though.  There
+is always more work to do.  But, just as importantly, most other
+participants in the Linux ecosystem can benefit through contributing to the
+kernel.  Getting code into the mainline is the key to higher code quality,
+lower maintenance and distribution costs, a higher level of influence over
+the direction of kernel development, and more.  It is a situation where
+everybody involved wins.  Fire up your editor and come join us; you will be
+more than welcome.