On Wed, Dec 02, 2015 at 12:27:25PM -0800, Kees Cook wrote: > The use of CONFIG_DEBUG_RODATA is generally seen as an essential part of > kernel self-protection: > http://www.openwall.com/lists/kernel-hardening/2015/11/30/13 > Additionally, its name has grown to mean things beyond just rodata. To > get ARM closer to this, we ought to rearrange the names of the configs > that control how the kernel protects its memory. What was called > CONFIG_ARM_KERNMEM_PERMS is really doing the work that other architectures > call CONFIG_DEBUG_RODATA. Kees, There is a subtle problem with the kernel memory permissions and the DMA debugging. DMA debugging checks whether we're trying to do DMA from the kernel mappings (text, rodata, data etc). It checks _text.._etext. However, when RODATA is enabled, we have about one section between _text and _stext which are freed into the kernel's page pool, and then become available for allocation and use for DMA. This then causes the DMA debugging sanity check to fire. So, I think I'll revert this change for the time being as it seems to be causing many people problems, and having this enabled is creating extra warnings when kernel debug options are enabled along with it. Sorry. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>