"Nicholas Piggin" <npig...@gmail.com> writes: > 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?
Yeah that should work. I'd be happier if we had something more explicit to document that boundary, I'll send a patch. cheers