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Russell Currey authored
commit a3f3072d 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: 3b10d009 ("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>
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