x86/cet: Check feature_1 in TCB for active IBT and SHSTK

Initially, IBT and SHSTK are marked as active when CPU supports them
and CET are enabled in glibc.  They can be disabled early by tunables
before relocation.  Since after relocation, GLRO(dl_x86_cpu_features)
becomes read-only, we can't update GLRO(dl_x86_cpu_features) to mark
IBT and SHSTK as inactive.  Instead, check the feature_1 field in TCB
to decide if IBT and SHST are active.

diff --git a/sysdeps/x86/bits/platform/x86.h b/sysdeps/x86/bits/platform/x86.h
index 1e23d53..1575ae5 100644 (file)
--- a/sysdeps/x86/bits/platform/x86.h
+++ b/sysdeps/x86/bits/platform/x86.h
@@ -337,3 +337,11 @@ enum
   x86_cpu_AVX10_YMM = x86_cpu_index_24_ecx_0_ebx + 17,
   x86_cpu_AVX10_ZMM = x86_cpu_index_24_ecx_0_ebx + 18,
 };
+
+/* Bits in the feature_1 field in TCB.  */
+
+enum
+{
+  x86_feature_1_ibt            = 1U << 0,
+  x86_feature_1_shstk          = 1U << 1
+};

diff --git a/sysdeps/x86/get-cpuid-feature-leaf.c b/sysdeps/x86/get-cpuid-feature-leaf.c
index 9317a6b..f69936b 100644 (file)
--- a/sysdeps/x86/get-cpuid-feature-leaf.c
+++ b/sysdeps/x86/get-cpuid-feature-leaf.c
@@ -15,9 +15,18 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-
+#include <assert.h>
+#include <tcb-offsets.h>
 #include <ldsodefs.h>
 
+#ifdef __x86_64__
+# ifdef __LP64__
+_Static_assert (FEATURE_1_OFFSET == 72, "FEATURE_1_OFFSET != 72");
+# else
+_Static_assert (FEATURE_1_OFFSET == 40, "FEATURE_1_OFFSET != 40");
+# endif
+#endif
+
 const struct cpuid_feature *
 __x86_get_cpuid_feature_leaf (unsigned int leaf)
 {

diff --git a/sysdeps/x86/sys/platform/x86.h b/sysdeps/x86/sys/platform/x86.h
index 1ea2c5f..89b1b16 100644 (file)
--- a/sysdeps/x86/sys/platform/x86.h
+++ b/sysdeps/x86/sys/platform/x86.h
@@ -45,6 +45,23 @@ x86_cpu_present (unsigned int __index)
 static __inline__ _Bool
 x86_cpu_active (unsigned int __index)
 {
+  if (__index == x86_cpu_IBT || __index == x86_cpu_SHSTK)
+    {
+#ifdef __x86_64__
+      unsigned int __feature_1;
+# ifdef __LP64__
+      __asm__ ("mov %%fs:72, %0" : "=r" (__feature_1));
+# else
+      __asm__ ("mov %%fs:40, %0" : "=r" (__feature_1));
+# endif
+      if (__index == x86_cpu_IBT)
+       return __feature_1 & x86_feature_1_ibt;
+      else
+       return __feature_1 & x86_feature_1_shstk;
+#else
+      return false;
+#endif
+    }
   const struct cpuid_feature *__ptr = __x86_get_cpuid_feature_leaf
     (__index / (8 * sizeof (unsigned int) * 4));
   unsigned int __reg