[PATCH 3/4] aarch64: Support enforcing BTI on dependencies

[Adhemerval Zanella Netto]

On 31/10/25 16:37, Yury Khrustalev wrote:
> ---
>  sysdeps/aarch64/dl-bti.c  | 18 ++++++++++++++++++
>  sysdeps/aarch64/linkmap.h |  1 +
>  2 files changed, 19 insertions(+)
> 
> diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
> index de6130470e..3d9f3653bc 100644
> --- a/sysdeps/aarch64/dl-bti.c
> +++ b/sysdeps/aarch64/dl-bti.c
> @@ -31,6 +31,10 @@
>  void
>  _dl_bti_protect (struct link_map *map, int fd)
>  {
> +

Spurious new line.

> +  /* If we try to enable BTI protection, MAP must be BTI marked.  */
> +  map->l_mach.bti = 1;

Maybe use 'true' instead?

> +
>    const size_t pagesz = GLRO(dl_pagesize);
>    const ElfW(Phdr) *phdr;
>  
> @@ -72,6 +76,10 @@ bti_failed (struct link_map *l, const char *program)
>  		      N_("failed to turn on BTI protection"));
>  }
>  
> +enum {
> +  BTI_CHECK_PERMISSIVE = 0,
> +  BTI_CHECK_ENFORCED = 1,
> +};
>  
>  /* Enable BTI for L and its dependencies.  */
>  
> @@ -84,10 +92,20 @@ _dl_bti_check (struct link_map *l, const char *program)
>    if (l->l_mach.bti_fail)
>      bti_failed (l, program);
>  
> +  /* We enforce BTI if tunable is set and if this object has BTI marking.  */
> +  bool enforce_bti = GLRO (dl_aarch64_bti) == BTI_CHECK_ENFORCED;

Maybe also change the '_dl_aarch64_bti' initialization
sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c to use BTI_CHECK_PERMISSIVE
instead.

> +
>    for (unsigned int i = 0; i < l->l_searchlist.r_nlist; i++)
>      {
>        struct link_map *dep = l->l_searchlist.r_list[i];
>        if (dep->l_mach.bti_fail)
>  	bti_failed (dep, program);
> +#ifdef SHARED
> +      /* Ignore BTI marking on ld.so: its properties are not processed.  */

Maybe state that kernel is responsible to setup BTI for the loader.

> +      if (is_rtld_link_map (dep->l_real))
> +        continue;
> +#endif
> +      if (enforce_bti && !dep->l_mach.bti)
> +        bti_failed (dep, program);
>      }
>  }
> diff --git a/sysdeps/aarch64/linkmap.h b/sysdeps/aarch64/linkmap.h
> index e56c890aea..4cd0492209 100644
> --- a/sysdeps/aarch64/linkmap.h
> +++ b/sysdeps/aarch64/linkmap.h
> @@ -24,4 +24,5 @@ struct link_map_machine
>    void *tlsdesc_table;	  /* Address of TLS descriptor hash table.  */
>    bool bti_fail;	  /* Failed to enable Branch Target Identification.  */
>    bool gcs;		  /* Guarded Control Stack marking.  */
> +  bool bti;		  /* Branch Target Identification marking.  */
>  };