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authorH.J. Lu <hjl.tools@gmail.com>2023-12-29 08:43:53 -0800
committerH.J. Lu <hjl.tools@gmail.com>2024-01-01 05:22:48 -0800
commit55d63e731253de82e96ed4ddca2e294076cd0bc5 (patch)
tree7bf46a0d70507206c236f946b45d15159687676c
parentd360dcc001cb12504cd3e8dbddee20df6bebb0f8 (diff)
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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.
-rw-r--r--sysdeps/x86/cpu-features.c2
-rw-r--r--sysdeps/x86/cpu-tunables.c15
2 files changed, 15 insertions, 2 deletions
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 142c6b9240..1742400525 100644
--- 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);
 	    }