On Thu Sep 15, 2022 at 10:47 PM AEST, Michael Ellerman wrote: > Nicholas Piggin <npig...@gmail.com> writes: > > powerpc has a number of read-only sections and tables that are put > > after RO_DATA(). Move the __end_rodata symbol to cover these as well. > > > > Setting memory to read-only at boot is done using __init_begin, > > change that that to use __end_rodata. > > Did you just do that because it seems logical?
I actually was looking at moving init so runtime code and data is closer. > Because it does seem logical, but it leaves a RWX region in the gap > between __end_rodata and __init_begin, which is bad. > > This is the current behaviour, on radix: > > ---[ Start of kernel VM ]--- > 0xc000000000000000-0xc000000001ffffff 0x0000000000000000 32M > r X pte valid present dirty accessed > 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M > r w pte valid present dirty accessed > > And with your change: > > ---[ Start of kernel VM ]--- > 0xc000000000000000-0xc0000000013fffff 0x0000000000000000 20M > r X pte valid present dirty accessed > 0xc000000001400000-0xc000000001ffffff 0x0000000001400000 12M > r w X pte valid present dirty accessed > 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M > r w pte valid present dirty accessed > > > On radix the 16M alignment is larger than we need, but we need to chose > a value at build time that works for radix and hash. > > We could make the code smarter on radix, to mark those pages in between > __end_rodata and __init_begin as RW_ and use them for data. But that > would be a more involved change. Ah, yes Christophe pointed out it's broken too. We could just align __end_rodata to STRICT_ALIGN_SIZE for this patch? Thanks, Nick