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Re: [PATCH] Ignore and remove LD_HWCAP_MASK for AT_SECURE programs (bug #21209)
- From: Carlos O'Donell <carlos at redhat dot com>
- To: Siddhesh Poyarekar <siddhesh at sourceware dot org>, libc-alpha at sourceware dot org
- Cc: fweimer at redhat dot com
- Date: Mon, 6 Mar 2017 09:55:16 -0500
- Subject: Re: [PATCH] Ignore and remove LD_HWCAP_MASK for AT_SECURE programs (bug #21209)
- Authentication-results: sourceware.org; auth=none
- References: <1488448740-1892-1-git-send-email-siddhesh@sourceware.org>
On 03/02/2017 04:59 AM, Siddhesh Poyarekar wrote:
> The LD_HWCAP_MASK environment variable may alter the selection of
> function variants for some architectures. For AT_SECURE process it
> means that if an outdated routine has a bug that would otherwise not
> affect newer platforms by default, LD_HWCAP_MASK will allow that bug
> to be exploited.
>
> To be on the safe side, ignore and disable LD_HWCAP_MASK for setuid
> binaries.
Agreed.
> [BZ #21209]
> * elf/rtld.c (process_envvars): Ignore LD_HWCAP_MASK for
> AT_SECURE processes.
> * sysdeps/generic/unsecvars.h: Add LD_HWCAP_MASK.
> * elf/tst-env-setuid.c (test_parent): Test LD_HWCAP_MASK.
> (test_child): Likewise.
> * elf/Makefile (tst-env-setuid-ENV): Add LD_HWCAP_MASK.
What about LD_HWCAP_MASK usage in ldconfig when creating the cache?
It appears that this could alter the hwcap-keyed platform directory
selection and also alter exactly which paths are searched.
> ---
> elf/Makefile | 3 ++-
> elf/rtld.c | 3 ++-
> elf/tst-env-setuid.c | 12 ++++++++++++
> sysdeps/generic/unsecvars.h | 1 +
> 4 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/elf/Makefile b/elf/Makefile
> index 61abeb5..cc4aeb2 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -1398,6 +1398,7 @@ $(objpfx)tst-nodelete-dlclose: $(objpfx)tst-nodelete-dlclose-dso.so
> $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
> $(objpfx)tst-nodelete-dlclose-plugin.so
>
> -tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096
> +tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
> + LD_HWCAP_MASK=0xffffffff
OK.
> tst-env-setuid-tunables-ENV = \
> GLIBC_TUNABLES=glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096
> diff --git a/elf/rtld.c b/elf/rtld.c
> index a036ece..5986eaf 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -2404,7 +2404,8 @@ process_envvars (enum mode *modep)
>
> case 10:
> /* Mask for the important hardware capabilities. */
> - if (memcmp (envline, "HWCAP_MASK", 10) == 0)
> + if (!__libc_enable_secure
> + && memcmp (envline, "HWCAP_MASK", 10) == 0)
OK.
> GLRO(dl_hwcap_mask) = __strtoul_internal (&envline[11], NULL,
> 0, 0);
> break;
> diff --git a/elf/tst-env-setuid.c b/elf/tst-env-setuid.c
> index 6ec3fa5..eec408e 100644
> --- a/elf/tst-env-setuid.c
> +++ b/elf/tst-env-setuid.c
> @@ -213,6 +213,12 @@ test_child (void)
> return 1;
> }
>
> + if (getenv ("LD_HWCAP_MASK") != NULL)
> + {
> + printf ("LD_HWCAP_MASK still set\n");
> + return 1;
> + }
OK.
> +
> return 0;
> }
> #endif
> @@ -233,6 +239,12 @@ test_parent (void)
> return 1;
> }
>
> + if (getenv ("LD_HWCAP_MASK") == NULL)
> + {
> + printf ("LD_HWCAP_MASK lost\n");
> + return 1;
> + }
Shouldn't this verify the value also?
> +
> return 0;
> }
> #endif
> diff --git a/sysdeps/generic/unsecvars.h b/sysdeps/generic/unsecvars.h
> index a740837..5ea8a4a 100644
> --- a/sysdeps/generic/unsecvars.h
> +++ b/sysdeps/generic/unsecvars.h
> @@ -16,6 +16,7 @@
> "LD_DEBUG\0" \
> "LD_DEBUG_OUTPUT\0" \
> "LD_DYNAMIC_WEAK\0" \
> + "LD_HWCAP_MASK\0" \
OK.
> "LD_LIBRARY_PATH\0" \
> "LD_ORIGIN_PATH\0" \
> "LD_PRELOAD\0" \
>
--
Cheers,
Carlos.