linux-kernel - Re: [PATCH v2 1/6] aarch64: Fix missing BTI protection from dependencies [BZ #26926]

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Date:   Thu, 10 Dec 2020 14:51:23 -0300
From:   Adhemerval Zanella <adhemerval.zanella@...aro.org>
To:     Szabolcs Nagy <szabolcs.nagy@....com>, libc-alpha@...rceware.org
Cc:     Mark Rutland <mark.rutland@....com>,
        kernel-hardening@...ts.openwall.com,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>,
        Mark Brown <broonie@...nel.org>,
        Topi Miettinen <toiwoton@...il.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/6] aarch64: Fix missing BTI protection from
 dependencies [BZ #26926]



On 27/11/2020 10:19, Szabolcs Nagy via Libc-alpha wrote:
> The _dl_open_check and _rtld_main_check hooks are not called on the
> dependencies of a loaded module, so BTI protection was missed on
> every module other than the main executable and directly dlopened
> libraries.
> 
> The fix just iterates over dependencies to enable BTI.
> 
> Fixes bug 26926.

LGTM, modulus the argument name change.

I also think it would be better to add a testcase, for both DT_NEEDED
and dlopen case.

> ---
>  sysdeps/aarch64/dl-bti.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
> index 196e462520..8f4728adce 100644
> --- a/sysdeps/aarch64/dl-bti.c
> +++ b/sysdeps/aarch64/dl-bti.c
> @@ -51,11 +51,24 @@ enable_bti (struct link_map *map, const char *program)
>    return 0;
>  }
>  
> -/* Enable BTI for L if required.  */
> +/* Enable BTI for MAP and its dependencies.  */
>  
>  void
> -_dl_bti_check (struct link_map *l, const char *program)
> +_dl_bti_check (struct link_map *map, const char *program)

I don't see much gain changing the argument name.

>  {
> -  if (GLRO(dl_aarch64_cpu_features).bti && l->l_mach.bti)
> -    enable_bti (l, program);
> +  if (!GLRO(dl_aarch64_cpu_features).bti)
> +    return;
> +
> +  if (map->l_mach.bti)
> +    enable_bti (map, program);
> +
> +  unsigned int i = map->l_searchlist.r_nlist;
> +  while (i-- > 0)
> +    {
> +      struct link_map *l = map->l_initfini[i];
> +      if (l->l_init_called)
> +	continue;
> +      if (l->l_mach.bti)
> +	enable_bti (l, program);
> +    }
>  }
> 

Ok.