Messages in this thread | | | Subject | Re: [PATCH] powerpc: fix alignment bug whithin the init sections | From | Christophe Leroy <> | Date | Fri, 18 Dec 2020 16:38:46 +0100 |
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Le 13/12/2020 à 19:35, Ariel Marcovitch a écrit : > This is a bug that can cause early crashes in configurations with a > .exit.text section smaller than a page and a .init.text section that > ends in the beginning of a physical page (this is kinda random, which > might explain why this wasn't really encountered before).
It can cause, or it causes ? Did you encounter the issue ?
> > 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.
> > 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"
> > Fixes: 060ef9d89d18 ("powerpc32: PAGE_EXEC required for inittext") > Signed-off-by: Ariel Marcovitch <ariel.marcovitch@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 ?
> /* .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
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