Ignore and remove LD_HWCAP_MASK for AT_SECURE programs (bug #21209)

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means that if an outdated routine has a bug that would otherwise not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.

	[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.

1 files changed, 2 insertions, 1 deletions

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)
 	    GLRO(dl_hwcap_mask) = __strtoul_internal (&envline[11], NULL,
 						      0, 0);
 	  break;