x86: Move x86-64 shadow stack startup codes

Move sysdeps/x86/libc-start.h to sysdeps/x86_64/libc-start.h and use
sysdeps/generic/libc-start.h for i386.
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 74 insertions, 0 deletions

diff --git a/sysdeps/x86_64/libc-start.h b/sysdeps/x86_64/libc-start.h
new file mode 100644
index 0000000..63fef17
--- /dev/null
+++ b/sysdeps/x86_64/libc-start.h
@@ -0,0 +1,74 @@
+/* x86-64 definitions for libc main startup.
+   Copyright (C) 2018-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef SHARED
+# define ARCH_SETUP_IREL() apply_irel ()
+# define ARCH_APPLY_IREL()
+# ifdef __CET__
+/* Get CET features enabled in the static executable.  */
+
+static inline unsigned int
+get_cet_feature (void)
+{
+  /* Check if CET is supported and not disabled by tunables.  */
+  const struct cpu_features *cpu_features = __get_cpu_features ();
+  unsigned int cet_feature = 0;
+  if (CPU_FEATURE_USABLE_P (cpu_features, IBT))
+    cet_feature |= GNU_PROPERTY_X86_FEATURE_1_IBT;
+  if (CPU_FEATURE_USABLE_P (cpu_features, SHSTK))
+    cet_feature |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
+  if (!cet_feature)
+    return cet_feature;
+
+  struct link_map *main_map = _dl_get_dl_main_map ();
+
+  /* Scan program headers backward to check PT_GNU_PROPERTY early for
+     x86 feature bits on static executable.  */
+  const ElfW(Phdr) *phdr = GL(dl_phdr);
+  const ElfW(Phdr) *ph;
+  for (ph = phdr + GL(dl_phnum); ph != phdr; ph--)
+    if (ph[-1].p_type == PT_GNU_PROPERTY)
+      {
+	_dl_process_pt_gnu_property (main_map, -1, &ph[-1]);
+	/* Enable IBT and SHSTK only if they are enabled on static
+	   executable.  */
+	cet_feature &= (main_map->l_x86_feature_1_and
+			& (GNU_PROPERTY_X86_FEATURE_1_IBT
+			   | GNU_PROPERTY_X86_FEATURE_1_SHSTK));
+	/* Set GL(dl_x86_feature_1) to the enabled CET features.  */
+	GL(dl_x86_feature_1) = cet_feature;
+	break;
+      }
+
+  return cet_feature;
+}
+
+/* The function using this macro to enable shadow stack must not return
+   to avoid shadow stack underflow.  */
+#  define ARCH_SETUP_TLS()						\
+  {									\
+    __libc_setup_tls ();						\
+									\
+    unsigned int cet_feature = get_cet_feature ();			\
+    ENABLE_X86_CET (cet_feature);					\
+    _dl_cet_setup_features (cet_feature);				\
+  }
+# else
+#  define ARCH_SETUP_TLS()	__libc_setup_tls ()
+# endif
+#endif /* !SHARED */