Re: [PATCH v4 07/10] x86/entry/vdso: include GNU_PROPERTY and GNU_STACK PHDRs

[Brian Gerst <brgerst@gmail.com>]

On Wed, Dec 17, 2025 at 9:16 PM Brian Gerst <brgerst@gmail.com> wrote:
>
> On Tue, Dec 16, 2025 at 4:26 PM H. Peter Anvin <hpa@zytor.com> wrote:
> >
> > Currently the vdso doesn't include .note.gnu.property or a GNU noexec
> > stack annotation (the -z noexecstack in the linker script is
> > ineffective because we specify PHDRs explicitly.)
> >
> > The motivation is that the dynamic linker currently do not check
> > these.
> >
> > However, this is a weak excuse: the vdso*.so are also supposed to be
> > usable at link libraries, and there is no reason why the dynamic
> > linker might not want or need to check these in the future, so add
> > them back in -- it is trivial enough.
> >
> > Use symbolic constants for the PHDR permission flags.
> >
> > [ v4: drop unrelated formatting changes ]
> >
> > Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> > ---
> >  arch/x86/entry/vdso/common/vdso-layout.lds.S | 38 ++++++++++++--------
> >  1 file changed, 23 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/x86/entry/vdso/common/vdso-layout.lds.S b/arch/x86/entry/vdso/common/vdso-layout.lds.S
> > index ec1ac191a057..a1e30be3e83d 100644
> > --- a/arch/x86/entry/vdso/common/vdso-layout.lds.S
> > +++ b/arch/x86/entry/vdso/common/vdso-layout.lds.S
> > @@ -47,18 +47,18 @@ SECTIONS
> >                 *(.gnu.linkonce.b.*)
> >         }                                               :text
> >
> > -       /*
> > -        * Discard .note.gnu.property sections which are unused and have
> > -        * different alignment requirement from vDSO note sections.
> > -        */
> > -       /DISCARD/ : {
> > +       .note.gnu.property : {
> >                 *(.note.gnu.property)
> > -       }
> > -       .note           : { *(.note.*) }                :text   :note
> > -
> > -       .eh_frame_hdr   : { *(.eh_frame_hdr) }          :text   :eh_frame_hdr
> > -       .eh_frame       : { KEEP (*(.eh_frame)) }       :text
> > +       }                                       :text :note :gnu_property
> > +       .note           : {
> > +               *(.note*)
> > +       }                                       :text :note
> >
> > +       .eh_frame_hdr   : { *(.eh_frame_hdr) }  :text :eh_frame_hdr
> > +       .eh_frame       : {
> > +               KEEP (*(.eh_frame))
> > +               *(.eh_frame.*)
> > +       }                                       :text
> >
> >         /*
> >          * Text is well-separated from actual data: there's plenty of
> > @@ -87,15 +87,23 @@ SECTIONS
> >   * Very old versions of ld do not recognize this name token; use the constant.
> >   */
> >  #define PT_GNU_EH_FRAME        0x6474e550
> > +#define PT_GNU_STACK   0x6474e551
> > +#define PT_GNU_PROPERTY        0x6474e553
>
> Do we even still support the old linkers that need these constants?

Digging into the binutils source, PT_GNU_EH_FRAME and PT_GNU_STACK
were added to the parser around bintils-2.15.  PT_GNU_PROPERTY was
added in binutils-2.38, which is newer than the minimum supported
version of binutils-2.30.

Probably better to just leave them then.


Brian Gerst