Re: [PATCH v5 02/27] x86/build: Remove RWX sections and align on 4KB

[Evgeniy Baskov]

On 2023-04-05 20:40, Borislav Petkov wrote:
> On Tue, Mar 14, 2023 at 01:13:29PM +0300, Evgeniy Baskov wrote:
> > Avoid creating sections simultaneously writable and readable to 
> > prepare
> > for W^X implementation for the kernel itself (not the decompressor).
> > Align kernel sections on page size (4KB) to allow protecting them in 
> > the
> > page tables.
> >
> > Split init code form ".init" segment into separate R_X ".inittext"
>
> s/form/from/

Thanks!

> > segment and make ".init" segment non-executable.
>
> "... and make the .init segment RW_."

Will fix.

> > Also add these segments to x86_32 architecture for consistency.
>
> Same comment as before: please refrain from talking about the *what* in
> a commit message but about the *why*.
>
> And considering the matter, you have a *lot* of *why* to talk about. 
> :-)
>
> Pls check your whole set.

I'll try do make descriptions of patches more elaborate and to better
reflect the reasoning behind the changes before resubmitting, thanks.

> > Currently paging is disabled in x86_32 in compressed kernel, so
> > protection is not applied anyways, but .init code was incorrectly
> > placed in non-executable ".data" segment. This should not change
> > anything meaningful in memory layout now, but might be required in 
> > case
> > memory protection will also be implemented in compressed kernel for
> > x86_32.
>
> I highly doubt that - no one cares about 32-bit x86 anymore.

True, but in theory it's still possible and also the change
makes things more correct.

> > @@ -226,9 +225,10 @@ SECTIONS
> >  #endif
> >
> >  	INIT_TEXT_SECTION(PAGE_SIZE)
> > -#ifdef CONFIG_X86_64
> > -	:init
> > -#endif
> > +	:inittext
> > +
> > +	. = ALIGN(PAGE_SIZE);
> > +
> >
> >  	/*
> >  	 * Section for code used exclusively before alternatives are run. 
> > All
> > @@ -240,6 +240,7 @@ SECTIONS
> >  	.altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
> >  		*(.altinstr_aux)
> >  	}
> > +	:init
>
> Why isn't this placed after inittext but here?

Because, AFAIK, :init is a part of a section syntax so it must
come after the brace, at least according to the documentation:

https://sourceware.org/binutils/docs/ld/PHDRS.html

> I'm thinking you wanna have:
>
> 	:inittext
> 	. = ALIGN..
> 	:init
> 	<rest>
>
> Thx.