[PATCH v2 07/10] arm64: asm: Provide a mechanism for generating ELF note for BTI

Mark Brown
2020-04-29T21:22:22Z

ELF files built for BTI should have a program property note section which
identifies them as such. The linker expects to find this note in all
object files it is linking into a BTI annotated output, the compiler will
ensure that this happens for C files but for assembler files we need to do
this in the source so provide a macro which can be used for this purpose.

This is mainly for use in the VDSO which should be a normal ELF shared
library and should therefore include BTI annotations when built for BTI.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/assembler.h | 41 ++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 0bff325117b4..85a88df2d0fe 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -736,4 +736,45 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
.Lyield_out_\@ :
.endm

+/*
+ * This macro emits a program property note section identifying
+ * architecture features which require special handling, mainly for
+ * use in assembly files included in the VDSO.
+ */
+
+#ifdef CONFIG_ARM64_BTI_KERNEL
+
+#define NT_GNU_PROPERTY_TYPE_0 5
+#define GNU_PROPERTY_AARCH64_FEATURE_1_AND 0xc0000000
+
+#define GNU_PROPERTY_AARCH64_FEATURE_1_BTI (1U << 0)
+#define GNU_PROPERTY_AARCH64_FEATURE_1_PAC (1U << 1)
+
+.macro emit_aarch64_feature_1_and
+ .pushsection .note.gnu.property, "a"
+ .align 3
+ .long 2f - 1f
+ .long 6f - 3f
+ .long NT_GNU_PROPERTY_TYPE_0
+1: .string "GNU"
+2:
+ .align 3
+3: .long GNU_PROPERTY_AARCH64_FEATURE_1_AND
+ .long 5f - 4f
+4:
+ .long GNU_PROPERTY_AARCH64_FEATURE_1_PAC | \
+ GNU_PROPERTY_AARCH64_FEATURE_1_BTI
+5:
+ .align 3
+6:
+ .popsection
+.endm
+
+#else
+
+.macro emit_aarch64_feature_1_and
+.endm
+
+#endif /* CONFIG_ARM64_BTI_KERNEL */
+
#endif /* __ASM_ASSEMBLER_H */
--
2.20.1