On Fri, Dec 18, 2020 at 5:39 PM Christophe Leroy < christophe.le...@csgroup.eu> wrote:
> It can cause, or it causes ? Did you encounter the issue ? > Yes, in configs that result in the section layout I described, the crush is consistent. > > > The init sections are ordered like this: > > .init.text > > .exit.text > > .init.data > > > > Currently, these sections aren't page aligned. > > > > Because the init code is mapped read-only at runtime and because the > > .init.text section can potentially reside on the same physical page as > > .init.data, the beginning of .init.data might be mapped read-only along > > with .init.text. > > init code is mapped PAGE_KERNEL_TEXT. > > Whether PAGE_KERNEL_TEXT is read-only or not depends on the selected > options. > You are right, of course. Should I change the commit message to 'might be mapped' or something? > > > Then when the kernel tries to modify a variable in .init.data (like > > kthreadd_done, used in kernel_init()) the kernel panics. > > > > To avoid this, I made these sections page aligned. > > Should write this unpersonal, something like "To avoid this, make these > sections page aligned" > Noted, thanks. > > > > > Fixes: 060ef9d89d18 ("powerpc32: PAGE_EXEC required for inittext") > > Signed-off-by: Ariel Marcovitch <ariel.marcovi...@gmail.com> > > --- > > arch/powerpc/kernel/vmlinux.lds.S | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/arch/powerpc/kernel/vmlinux.lds.S > b/arch/powerpc/kernel/vmlinux.lds.S > > index 326e113d2e45..e3a7c90c03f4 100644 > > --- a/arch/powerpc/kernel/vmlinux.lds.S > > +++ b/arch/powerpc/kernel/vmlinux.lds.S > > @@ -179,6 +179,11 @@ SECTIONS > > #endif > > } :text > > > > + /* .init.text is made RO and .exit.text is not, so we must > > + * ensure these sections reside in separate physical pages. > > + */ > > + . = ALIGN(PAGE_SIZE); > > + > > In principle, as it is text, it should be made RO as well. But what > happens at the begining doesn't > really matter, anyway .exit.text should never be executed and is discarded > together with init text. > So, I think it is OK the live with it as is for the time being. > Making it page aligned makes sense anyway. > > Should we make _einittext page aligned instead, just like _etext ? Yes, this will probably be better (because when _einittext is not aligned, the part of the page after _einittext is mapped RO implicitly, and it's hard to notice from the code). I suppose you mean something like this: _sinittext = .; INIT_TEXT + + . = ALIGN(.); _einittext = .; > /* .exit.text is discarded at runtime, not link time, > > * to deal with references from __bug_table > > */ > > @@ -186,6 +191,8 @@ SECTIONS > > EXIT_TEXT > > } > > > > + . = ALIGN(PAGE_SIZE); > > + > > Here for sure, as you explain in the coming log, this needs to be > separated from init text. So > making it aligned is a must. > > .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { > > INIT_DATA > > } > > > > base-commit: 1398820fee515873379809a6415930ad0764b2f6 > > > > Christophe > Thanks for your time, Ariel Marcovitch