On Mon, 2019-06-03 at 08:20:28 UTC, Christophe Leroy wrote: > In the old days, _PAGE_EXEC didn't exist on 6xx aka book3s/32. > Therefore, allthough __mapin_ram_chunk() was already mapping kernel > text with PAGE_KERNEL_TEXT and the rest with PAGE_KERNEL, the entire > memory was executable. Part of the memory (first 512kbytes) was > mapped with BATs instead of page table, but it was also entirely > mapped as executable. > > In commit 385e89d5b20f ("powerpc/mm: add exec protection on > powerpc 603"), we started adding exec protection to some 6xx, namely > the 603, for pages mapped via pagetables. > > Then, in commit 63b2bc619565 ("powerpc/mm/32s: Use BATs for > STRICT_KERNEL_RWX"), the exec protection was extended to BAT mapped > memory, so that really only the kernel text could be executed. > > The problem here is that kexec is based on copying some code into > upper part of memory then executing it from there in order to install > a fresh new kernel at its definitive location. > > However, the code is position independant and first part of it is > just there to deactivate the MMU and jump to the second part. So it > is possible to run this first part inplace instead of running the > copy. Once the MMU is off, there is no protection anymore and the > second part of the code will just run as before. > > Reported-by: Aaro Koskinen <aaro.koski...@iki.fi> > Fixes: 63b2bc619565 ("powerpc/mm/32s: Use BATs for STRICT_KERNEL_RWX") > Cc: sta...@vger.kernel.org > Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr> > Tested-by: Aaro Koskinen <aaro.koski...@iki.fi>
Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/6c284228eb356a1ec62a704b4d232971 cheers