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

[Brian Gerst <brgerst@gmail.com>]

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?


Brian Gerst