Enable BTI in bionic linker

This patch adds support to load BTI-enabled objects.

According to the ABI, BTI is recorded in the .note.gnu.property section.
The new parser evaluates the property section, if exists.
It searches for .note section with NT_GNU_PROPERTY_TYPE_0.
Once found it tries to find GNU_PROPERTY_AARCH64_FEATURE_1_AND.
The results are cached.

The main change in linker is when protection of loaded ranges gets
applied. When BTI is requested and the platform also supports it
the prot flags have to be amended with PROT_BTI for executable ranges.
Failing to add PROT_BTI flag would disable BTI protection.
Moreover, adding the new PROT flag for shared objects without BTI
compatibility would break applications.

Kernel does not add PROT_BTI to a loaded ELF which has interpreter.
Linker handles this case too.

Test: 1. Flame boots
      2. Tested on FVP with BTI enabled

Change-Id: Iafdf223b74c6e75d9f17ca90500e6fe42c4c1218

1 files changed, 8 insertions, 0 deletions

diff --git a/linker/linker.cpp b/linker/linker.cpp
index 302e4b3f9..77f754cf4 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -3141,6 +3141,14 @@ bool soinfo::prelink_image() {
         // resolves everything eagerly, so these can be ignored.
         break;
 
+#if defined(__aarch64__)
+      case DT_AARCH64_BTI_PLT:
+      case DT_AARCH64_PAC_PLT:
+      case DT_AARCH64_VARIANT_PCS:
+        // Ignored: AArch64 processor-specific dynamic array tags.
+        break;
+#endif
+
       default:
         if (!relocating_linker) {
           const char* tag_name;