af2db2a1e7
commit a3f3072db6cad40895c585dce65e36aab997f042 upstream.
Without restoring the IAMR after idle, execution prevention on POWER9
with Radix MMU is overwritten and the kernel can freely execute
userspace without faulting.
This is necessary when returning from any stop state that modifies
user state, as well as hypervisor state.
To test how this fails without this patch, load the lkdtm driver and
do the following:
$ echo EXEC_USERSPACE > /sys/kernel/debug/provoke-crash/DIRECT
which won't fault, then boot the kernel with powersave=off, where it
will fault. Applying this patch will fix this.
Fixes: 3b10d0095a1e ("powerpc/mm/radix: Prevent kernel execution of user space")
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.