diff mbox series

[16/17] x86/cet: Don't set CET active by default

Message ID 20231206172010.1023415-17-hjl.tools@gmail.com
State New
Headers show
Series x86/cet: Update CET kernel interface | expand

Commit Message

H.J. Lu Dec. 6, 2023, 5:20 p.m. UTC 
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.
---
 sysdeps/x86/cpu-features.c |  2 +-
 sysdeps/x86/cpu-tunables.c | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 097868c1d9..80a07ac589 100644
--- 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 5697885226..8f4f25efb0 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -34,6 +34,18 @@ 
       break;								\
     }
 
+#define CHECK_GLIBC_IFUNC_CPU_BOTH(f, cpu_features, name,		\
+				   disable, len)			\
+  _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
+  if (memcmp (f, #name, len) == 0)					\
+    {									\
+      if (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)	\
@@ -149,11 +161,14 @@  TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  break;
 	case 5:
+	  {
+	    CHECK_GLIBC_IFUNC_CPU_BOTH (n, cpu_features, SHSTK, disable,
+					5);
+	  }
 	  if (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);
 	    }