[glibc/arm/gcs] aarch64: Add glibc.cpu.aarch64_gcs tunable

[glibc/arm/gcs] aarch64: Add glibc.cpu.aarch64_gcs tunable

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=200010339f4fa0449a7bd76555931881eaea916c

commit 200010339f4fa0449a7bd76555931881eaea916c
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Mon Jul 17 08:31:05 2023 +0100

    aarch64: Add glibc.cpu.aarch64_gcs tunable
    
    This tunable is for controlling the GCS status. It is the argument to
    the PR_SET_SHADOW_STACK_STATUS prctl, by default 0, so GCS is disabled.
    
    The status is stored into GL(dl_aarch64_gcs) early and only applied
    later, since enabling GCS is tricky: it must happen on a top level
    stack frame. (Using GL instead of GLRO because it may need updates
    depending on loaded libraries that happen after readonly protection
    is applied, however library marking based GCS setting is not yet
    implemented.)

Diff:
---
 sysdeps/aarch64/dl-tunables.list                 |  5 ++++
 sysdeps/unix/sysv/linux/aarch64/cpu-features.c   |  4 +++
 sysdeps/unix/sysv/linux/aarch64/dl-procruntime.c | 37 ++++++++++++++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/sysdeps/aarch64/dl-tunables.list b/sysdeps/aarch64/dl-tunables.list
index 92c6cbfa92..c08be86932 100644
--- a/sysdeps/aarch64/dl-tunables.list
+++ b/sysdeps/aarch64/dl-tunables.list
@@ -21,5 +21,10 @@ glibc {
     name {
       type: STRING
     }
+    aarch64_gcs {
+      type: UINT_64
+      minval: 0
+      default: 0
+    }
   }
 }
diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
index b1a3f673f0..a8b6a4654a 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -128,4 +128,8 @@ init_cpu_features (struct cpu_features *cpu_features)
 
   /* Check if MOPS is supported.  */
   cpu_features->mops = GLRO (dl_hwcap2) & HWCAP2_MOPS;
+
+  if (GLRO (dl_hwcap2) & HWCAP2_GCS)
+    /* GCS status may be updated later by binary compatibility checks.  */
+    GL (dl_aarch64_gcs) = TUNABLE_GET (glibc, cpu, aarch64_gcs, uint64_t, 0);
 }
diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procruntime.c b/sysdeps/unix/sysv/linux/aarch64/dl-procruntime.c
new file mode 100644
index 0000000000..23c61da6c4
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/dl-procruntime.c
@@ -0,0 +1,37 @@
+/* Data for processor runtime information.  AArch64 version.
+   Copyright (C) 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 PROCINFO_CLASS
+# define PROCINFO_CLASS
+#endif
+
+#if !IS_IN (ldconfig)
+# if !defined PROCINFO_DECL && defined SHARED
+  ._dl_aarch64_gcs
+# else
+PROCINFO_CLASS unsigned long _dl_aarch64_gcs
+# endif
+# ifndef PROCINFO_DECL
+= 0
+# endif
+# if !defined SHARED || defined PROCINFO_DECL
+;
+# else
+,
+# endif
+#endif