[PATCH v3 2/4] aarch64: Add glibc.cpu.aarch64_bti tunable

[Yury Khrustalev]

---
 manual/tunables.texi                           | 16 ++++++++++++++++
 sysdeps/aarch64/dl-tunables.list               |  6 ++++++
 sysdeps/unix/sysv/linux/aarch64/cpu-features.c |  2 ++
 sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c  | 16 ++++++++++++++++
 4 files changed, 40 insertions(+)

diff --git a/manual/tunables.texi b/manual/tunables.texi
index 4d3c6e9933..cbbde8f412 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -598,6 +598,22 @@ This tunable is specific to x86-64 and effective only when the lazy
 binding is disabled.
 @end deftp
 
+@deftp Tunable glibc.cpu.aarch64_bti
+This tunable controls Branch Target Identification (BTI) handling for the
+process. This handling is implemented via protecting the memory mapping
+with @code{PROT_BTI} for modules that are marked with the appropriate ELF
+property.
+
+Accepted values are:
+
+0 = permissive: BTI protection is enabled only for modules that have BTI
+marking (default).
+
+1 = enforced: if a module that does not have BTI marking is loaded, it is
+an error (either a process abort or a @code{dlopen} error if this binary
+is loaded via @code{dlopen}).
+@end deftp
+
 @deftp Tunable glibc.cpu.aarch64_gcs
 This tunable controls Guarded Control Stack (GCS) for the process.
 
diff --git a/sysdeps/aarch64/dl-tunables.list b/sysdeps/aarch64/dl-tunables.list
index d461c1e9db..40757ac046 100644
--- a/sysdeps/aarch64/dl-tunables.list
+++ b/sysdeps/aarch64/dl-tunables.list
@@ -21,6 +21,12 @@ glibc {
     name {
       type: STRING
     }
+    aarch64_bti {
+      type: UINT_64
+      minval: 0
+      maxval: 1
+      default: 0
+    }
     aarch64_gcs {
       type: UINT_64
       minval: 0
diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
index 1acc82d077..a05a4ce794 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -137,6 +137,8 @@ init_cpu_features (struct cpu_features *cpu_features)
 
   /* Check if BTI is supported.  */
   cpu_features->bti = GLRO (dl_hwcap2) & HWCAP2_BTI;
+  if (cpu_features->bti)
+    GLRO (dl_aarch64_bti) = TUNABLE_GET (glibc, cpu, aarch64_bti, uint64_t, 0);
 
   /* Setup memory tagging support if the HW and kernel support it, and if
      the user has requested it.  */
diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
index 20966e0478..20083b1475 100644
--- a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
+++ b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
@@ -56,5 +56,21 @@ PROCINFO_CLASS struct cpu_features _dl_aarch64_cpu_features
 # endif
 #endif
 
+#if !IS_IN (ldconfig)
+# if !defined PROCINFO_DECL && defined SHARED
+  ._dl_aarch64_bti
+# else
+PROCINFO_CLASS unsigned long _dl_aarch64_bti
+# endif
+# ifndef PROCINFO_DECL
+= 0
+# endif
+# if !defined SHARED || defined PROCINFO_DECL
+;
+# else
+,
+# endif
+#endif
+
 #undef PROCINFO_DECL
 #undef PROCINFO_CLASS
-- 
2.47.3