[OpenMP][AArch64] Fix branch protection in microtasks

[tuliom]

Start __kmp_invoke_microtask with PACBTI in order to identify the function as a valid branch target. Before returning, SP is authenticated.
Also add the BTI and PAC markers to z_Linux_asm.S.

With this patch, libomp.so can now be generated with DT_AARCH64_BTI_PLT when built with -mbranch-protection=standard.

The implementation is based on the code available in compiler-rt.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Tulio Magno Quites Machado Filho (tuliom)

Changes

Start __kmp_invoke_microtask with BTI in order to identify the function as a valid branch target.
Also add the BTI marker to z_Linux_asm.S.

With this patch, libomp.so can now be generated with DT_AARCH64_BTI_PLT when built with -mbranch-protection=standard.

The implementation is based on the code available in compiler-rt.

---

Full diff: https://github.com/llvm/llvm-project/pull/102317.diff

1 Files Affected:

• (modified) openmp/runtime/src/z_Linux_asm.S (+45)

diff --git a/openmp/runtime/src/z_Linux_asm.S b/openmp/runtime/src/z_Linux_asm.S
index f119f64647daa4..f7ed3ada982f6f 100644
--- a/openmp/runtime/src/z_Linux_asm.S
+++ b/openmp/runtime/src/z_Linux_asm.S
@@ -17,6 +17,27 @@
 
 #include "kmp_config.h"
 
+#if KMP_OS_LINUX
+// BTI and PAC gnu property note
+#define NT_GNU_PROPERTY_TYPE_0 5
+#define GNU_PROPERTY_AARCH64_FEATURE_1_AND 0xc0000000
+#define GNU_PROPERTY_AARCH64_FEATURE_1_BTI 1
+#define GNU_PROPERTY_AARCH64_FEATURE_1_PAC 2
+
+# define GNU_PROPERTY(type, value)                                             \
+  .pushsection .note.gnu.property, "a";                                        \
+  .p2align 3;                                                                  \
+  .word 4;                                                                     \
+  .word 16;                                                                    \
+  .word NT_GNU_PROPERTY_TYPE_0;                                                \
+  .asciz "GNU";                                                                \
+  .word type;                                                                  \
+  .word 4;                                                                     \
+  .word value;                                                                 \
+  .word 0;                                                                     \
+  .popsection
+#endif
+
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
 
 # if KMP_MIC
@@ -176,6 +197,25 @@ KMP_PREFIX_UNDERSCORE(\proc):
 .endm
 # endif // KMP_OS_DARWIN
 
+# if defined(__ARM_FEATURE_BTI_DEFAULT)
+#  define BTI_FLAG GNU_PROPERTY_AARCH64_FEATURE_1_BTI
+# else
+#  define BTI_FLAG 0
+# endif
+# if __ARM_FEATURE_PAC_DEFAULT & 3
+#  define PAC_FLAG GNU_PROPERTY_AARCH64_FEATURE_1_PAC
+# else
+#  define PAC_FLAG 0
+# endif
+
+# if (BTI_FLAG | PAC_FLAG) != 0
+#  define BTI_C hint #34
+#  define GNU_PROPERTY_BTI_PAC \
+    GNU_PROPERTY(GNU_PROPERTY_AARCH64_FEATURE_1_AND, BTI_FLAG | PAC_FLAG)
+# else
+#  define BTI_C
+#  define GNU_PROPERTY_BTI_PAC
+# endif
 #endif // (KMP_OS_LINUX || KMP_OS_DARWIN || KMP_OS_WINDOWS) && (KMP_ARCH_AARCH64 || KMP_ARCH_AARCH64_32 || KMP_ARCH_ARM)
 
 .macro COMMON name, size, align_power
@@ -1296,6 +1336,7 @@ __tid = 8
 // mark_begin;
 	.text
 	PROC __kmp_invoke_microtask
+	BTI_C
 
 	stp	x29, x30, [sp, #-16]!
 # if OMPT_SUPPORT
@@ -2452,3 +2493,7 @@ KMP_PREFIX_UNDERSCORE(__kmp_unnamed_critical_addr):
 .section .note.GNU-stack,"",@progbits
 # endif
 #endif
+
+#if KMP_OS_LINUX && (KMP_ARCH_AARCH64 || KMP_ARCH_AARCH64_32)
+GNU_PROPERTY_BTI_PAC
+#endif

[tuliom]

I updated the description in order to reflect my latest change.

[davemgreen]

(I'm not really a pac-bti expert, but the changes look like they might well be sensible. Hopefully one of the other reviewers added can check and see).

[DanielKristofKiss]

just a small suggestion, LGTM otherwise.

[tuliom]

/cherry-pick 0aa22dc

[llvmbot]

Failed to cherry-pick: 0aa22dc

https://github.com/llvm/llvm-project/actions/runs/10375652579

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request

[tuliom]

I manually backported this patch to release/19.x and opened #103491.