On Wed, 2020-02-26 at 18:16 +1100, Daniel Axtens wrote: > Hi Jason, > > > This is a try to implement KASLR for Freescale BookE64 which is based on > > my earlier implementation for Freescale BookE32: > > https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=131718 > > > > The implementation for Freescale BookE64 is similar as BookE32. One > > difference is that Freescale BookE64 set up a TLB mapping of 1G during > > booting. Another difference is that ppc64 needs the kernel to be > > 64K-aligned. So we can randomize the kernel in this 1G mapping and make > > it 64K-aligned. This can save some code to creat another TLB map at > > early boot. The disadvantage is that we only have about 1G/64K = 16384 > > slots to put the kernel in. > > > > KERNELBASE > > > > 64K |--> kernel <--| > > | | | > > +--+--+--+ +--+--+--+--+--+--+--+--+--+ +--+--+ > > | | | |....| | | | | | | | | |....| | | > > +--+--+--+ +--+--+--+--+--+--+--+--+--+ +--+--+ > > | | 1G > > |-----> offset <-----| > > > > kernstart_virt_addr > > > > I'm not sure if the slot numbers is enough or the design has any > > defects. If you have some better ideas, I would be happy to hear that. > > > > Thank you all. > > > > Are you making any attempt to hide kernel address leaks in this series? > I've just been looking at the stackdump code just now, and it directly > prints link registers and stack pointers, which is probably enough to > determine the kernel base address: > > SPs: LRs: %pS pointer > [ 0.424506] [c0000000de403970] [c000000001fc0458] dump_stack+0xfc/0x154 > (unreliable) > [ 0.424593] [c0000000de4039c0] [c000000000267eec] panic+0x258/0x5ac > [ 0.424659] [c0000000de403a60] [c0000000024d7a00] > mount_block_root+0x634/0x7c0 > [ 0.424734] [c0000000de403be0] [c0000000024d8100] > prepare_namespace+0x1ec/0x23c > [ 0.424811] [c0000000de403c60] [c0000000024d7010] > kernel_init_freeable+0x804/0x880 > > git grep \\\"REG\\\" arch/powerpc shows a few other uses like this, all > in process.c or in xmon. > > Maybe replacing the REG format string in KASLR mode would be sufficient? Whatever we decide to do here, it's not book3e-specific so it should be considered separately from these patches. -Scott
