[PATCH v2 3/4] aarch64: Support enforcing BTI on dependencies

[Yury Khrustalev]

---
 sysdeps/aarch64/cpu-features.h                |  5 +++++
 sysdeps/aarch64/dl-bti.c                      | 16 +++++++++++++++-
 sysdeps/aarch64/linkmap.h                     |  1 +
 sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c |  2 +-
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/sysdeps/aarch64/cpu-features.h b/sysdeps/aarch64/cpu-features.h
index ef4e947e8c..855990b575 100644
--- a/sysdeps/aarch64/cpu-features.h
+++ b/sysdeps/aarch64/cpu-features.h
@@ -54,6 +54,11 @@
 			     || (MIDR_PARTNUM(midr) == 0x002		\
 			         && MIDR_VARIANT(midr) == 0)))
 
+enum {
+  BTI_CHECK_PERMISSIVE = 0,
+  BTI_CHECK_ENFORCED = 1,
+};
+
 struct cpu_features
 {
   uint64_t midr_el1;
diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
index de6130470e..3215a4575b 100644
--- a/sysdeps/aarch64/dl-bti.c
+++ b/sysdeps/aarch64/dl-bti.c
@@ -31,6 +31,9 @@
 void
 _dl_bti_protect (struct link_map *map, int fd)
 {
+  /* If we try to enable BTI protection, MAP must be BTI marked.  */
+  map->l_mach.bti = true;
+
   const size_t pagesz = GLRO(dl_pagesize);
   const ElfW(Phdr) *phdr;
 
@@ -72,7 +75,6 @@ bti_failed (struct link_map *l, const char *program)
 		      N_("failed to turn on BTI protection"));
 }
 
-
 /* Enable BTI for L and its dependencies.  */
 
 void
@@ -84,10 +86,22 @@ _dl_bti_check (struct link_map *l, const char *program)
   if (l->l_mach.bti_fail)
     bti_failed (l, program);
 
+  /* We enforce BTI if tunable is set and if this object has BTI marking.  */
+  bool enforce_bti = GLRO (dl_aarch64_bti) == BTI_CHECK_ENFORCED;
+
   for (unsigned int i = 0; i < l->l_searchlist.r_nlist; i++)
     {
       struct link_map *dep = l->l_searchlist.r_list[i];
       if (dep->l_mach.bti_fail)
 	bti_failed (dep, program);
+#ifdef SHARED
+      /* Ignore BTI marking on ld.so: its properties are not processed and
+         kernel is responsible for setting up BTI protection for the
+         loader.  */
+      if (is_rtld_link_map (dep->l_real))
+        continue;
+#endif
+      if (enforce_bti && !dep->l_mach.bti)
+        bti_failed (dep, program);
     }
 }
diff --git a/sysdeps/aarch64/linkmap.h b/sysdeps/aarch64/linkmap.h
index e56c890aea..4cd0492209 100644
--- a/sysdeps/aarch64/linkmap.h
+++ b/sysdeps/aarch64/linkmap.h
@@ -24,4 +24,5 @@ struct link_map_machine
   void *tlsdesc_table;	  /* Address of TLS descriptor hash table.  */
   bool bti_fail;	  /* Failed to enable Branch Target Identification.  */
   bool gcs;		  /* Guarded Control Stack marking.  */
+  bool bti;		  /* Branch Target Identification marking.  */
 };
diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
index 20083b1475..7c34c8ddba 100644
--- a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
+++ b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
@@ -63,7 +63,7 @@ PROCINFO_CLASS struct cpu_features _dl_aarch64_cpu_features
 PROCINFO_CLASS unsigned long _dl_aarch64_bti
 # endif
 # ifndef PROCINFO_DECL
-= 0
+= BTI_CHECK_PERMISSIVE
 # endif
 # if !defined SHARED || defined PROCINFO_DECL
 ;
-- 
2.47.3