Re: [PATCH v4 02/26] x86/build: Remove RWX sections and align on 4KB

[Evgeniy Baskov]

On 2023-03-10 17:45, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
> > Avoid creating sections simultaneously writable and readable
> > to prepare for W^X implementation. Align sections on page size (4KB) 
> > to
> > allow protecting them in the page tables.
> >
> > Split init code form ".init" segment into separate R_X ".inittext"
> > segment and make ".init" segment non-executable.
> >
> > Also add these segments to x86_32 architecture for consistency.
> > 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.
> >
> > Tested-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > Tested-by: Peter Jones <pjones@xxxxxxxxxx>
> > Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
>
> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> One nit: the series modifies both the decompressor linker script and
> the core kernel one, so please make it very explicit in the commit log
> which one is being modified, and why it matters for this particular
> context.

Thanks! I'll amend the log.
> > ---
> >  arch/x86/kernel/vmlinux.lds.S | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kernel/vmlinux.lds.S 
> > b/arch/x86/kernel/vmlinux.lds.S
> > index 2e0ee14229bf..2e56d694c491 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -102,12 +102,11 @@ jiffies = jiffies_64;
> >  PHDRS {
> >         text PT_LOAD FLAGS(5);          /* R_E */
> >         data PT_LOAD FLAGS(6);          /* RW_ */
> > -#ifdef CONFIG_X86_64
> > -#ifdef CONFIG_SMP
> > +#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
> >         percpu PT_LOAD FLAGS(6);        /* RW_ */
> >  #endif
> > -       init PT_LOAD FLAGS(7);          /* RWE */
> > -#endif
> > +       inittext PT_LOAD FLAGS(5);      /* R_E */
> > +       init PT_LOAD FLAGS(6);          /* RW_ */
> >         note PT_NOTE FLAGS(0);          /* ___ */
> >  }
> >
> > @@ -227,9 +226,10 @@ 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
> > @@ -241,6 +241,7 @@ SECTIONS
> >         .altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
> >                 *(.altinstr_aux)
> >         }
> > +       :init
> >
> >         INIT_DATA_SECTION(16)
> >
> > --
> > 2.37.4