Re: [PATCH 01/16] x86/boot: Align vmlinuz sections on page size

[Evgeniy Baskov]

On 2022-10-19 10:01, Ard Biesheuvel wrote:
> On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
> > To protect sections on page table level each section
> > needs to be aligned on page size (4KB).
> >
> > Set sections alignment in linker script.
> >
> > Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
> > ---
> >  arch/x86/boot/compressed/vmlinux.lds.S | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S 
> > b/arch/x86/boot/compressed/vmlinux.lds.S
> > index 112b2375d021..6be90f1a1198 100644
> > --- a/arch/x86/boot/compressed/vmlinux.lds.S
> > +++ b/arch/x86/boot/compressed/vmlinux.lds.S
> > @@ -27,21 +27,27 @@ SECTIONS
> >                 HEAD_TEXT
> >                 _ehead = . ;
> >         }
> > +       . = ALIGN(PAGE_SIZE);
> >         .rodata..compressed : {
> > +               _compressed = .;
>
> Why are you adding these?

It is used for address compressed kernel blob during memory protection 
setup.
Although it can be addressed via different symbols, I though that 
addressing
sections data in a common way (through linker generated symbols) would 
be better.
I can remove or mention the change in commit message (for now I will do 
the latter).

> >                 *(.rodata..compressed)
> > +               _ecompressed = .;
> >         }
> > +       . = ALIGN(PAGE_SIZE);
>
> On other EFI architectures, we only distinguish between R-X and RW-
> regions, and alignment between .rodata and .text is unnecessary. Do we
> really need to deviate from that here?

I though that leaving a huge compressed kernel blob executable is
undesirable, so I decided to split it out. I can make it either RW- or 
R-X
if it would be more acceptable.

> >         .text : {
> >                 _text = .;      /* Text */
> >                 *(.text)
> >                 *(.text.*)
> >                 _etext = . ;
> >         }
> > +       . = ALIGN(PAGE_SIZE);
> >         .rodata : {
> >                 _rodata = . ;
> >                 *(.rodata)       /* read-only data */
> >                 *(.rodata.*)
> >                 _erodata = . ;
> >         }
> > +       . = ALIGN(PAGE_SIZE);
> >         .data : {
> >                 _data = . ;
> >                 *(.data)
> > --
> > 2.35.1