x86/cet: Don't set CET active by default

Not all CET enabled applications and libraries have been properly tested
in CET enabled environments.  Some CET enabled applications or libraries
will crash or misbehave when CET is enabled.  Don't set CET active by
default so that all applications and libraries will run normally regardless
of whether CET is active or not.  Shadow stack can be enabled by

$ export GLIBC_TUNABLES=glibc.cpu.hwcaps=SHSTK

at run-time if shadow stack can be enabled by kernel.

NB: This commit can be reverted if it is OK to enable CET by default for
all applications and libraries.

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 097868c..80a07ac 100644 (file)
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -110,7 +110,7 @@ update_active (struct cpu_features *cpu_features)
   if (!CPU_FEATURES_CPU_P (cpu_features, RTM_ALWAYS_ABORT))
     CPU_FEATURE_SET_ACTIVE (cpu_features, RTM);
 
-#if CET_ENABLED
+#if CET_ENABLED && 0
   CPU_FEATURE_SET_ACTIVE (cpu_features, IBT);
   CPU_FEATURE_SET_ACTIVE (cpu_features, SHSTK);
 #endif

diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 142c6b9..1742400 100644 (file)
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -35,6 +35,17 @@
       break;                                                           \
     }
 
+#define CHECK_GLIBC_IFUNC_CPU_BOTH(f, cpu_features, name, len)         \
+  _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);       \
+  if (tunable_str_comma_strcmp_cte (&f, #name))                                \
+    {                                                                  \
+      if (f.disable)                                                   \
+       CPU_FEATURE_UNSET (cpu_features, name)                          \
+      else                                                             \
+       CPU_FEATURE_SET_ACTIVE (cpu_features, name)                     \
+      break;                                                           \
+    }
+
 /* Disable a preferred feature NAME.  We don't enable a preferred feature
    which isn't available.  */
 #define CHECK_GLIBC_IFUNC_PREFERRED_OFF(f, cpu_features, name, len)    \
@@ -131,11 +142,13 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
            }
          break;
        case 5:
+         {
+           CHECK_GLIBC_IFUNC_CPU_BOTH (n, cpu_features, SHSTK, 5);
+         }
          if (n.disable)
            {
              CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, LZCNT, 5);
              CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
-             CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SHSTK, 5);
              CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSSE3, 5);
              CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, XSAVE, 5);
            }