[PATCH v3 03/11] arm64: asm: Override SYM_FUNC_START when building the kernel with BTI

Mark Brown
2020-05-06T19:52:45Z

When the kernel is built for BTI override SYM_FUNC_START and related macros
to add a BTI landing pad to the start of all global functions, ensuring that
they are BTI safe. The ; at the end of the BTI_x macros is for the
benefit of the macro-generated functions in xen-hypercall.S.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/linkage.h | 46 ++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)

diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index ebee3113a62f..b5a7998a6b2a 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -4,6 +4,52 @@
#define __ALIGN .align 2
#define __ALIGN_STR ".align 2"

+#if defined(CONFIG_ARM64_BTI_KERNEL) && defined(__aarch64__)
+
+/*
+ * Since current versions of gas reject the BTI instruction unless we
+ * set the architecture version to v8.5 we use the hint instruction
+ * instead.
+ */
+#define BTI_C hint 34 ;
+#define BTI_J hint 36 ;
+
+/*
+ * When using in-kernel BTI we need to ensure that assembly functions
+ * have suitable annotations. Override SYM_FUNC_START to insert a BTI
+ * landing pad at the start of everything.
+ */
+#define SYM_FUNC_START(name) \
+ SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
+ BTI_C
+
+#define SYM_FUNC_START_NOALIGN(name) \
+ SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE) \
+ BTI_C
+
+#define SYM_FUNC_START_LOCAL(name) \
+ SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN) \
+ BTI_C
+
+#define SYM_FUNC_START_LOCAL_NOALIGN(name) \
+ SYM_START(name, SYM_L_LOCAL, SYM_A_NONE) \
+ BTI_C
+
+#define SYM_FUNC_START_WEAK(name) \
+ SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN) \
+ BTI_C
+
+#define SYM_FUNC_START_WEAK_NOALIGN(name) \
+ SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \
+ BTI_C
+
+#define SYM_INNER_LABEL(name, linkage) \
+ .type name SYM_T_NONE ASM_NL \
+ SYM_ENTRY(name, linkage, SYM_A_NONE) \
+ BTI_J
+
+#endif
+
/*
* Annotate a function as position independent, i.e., safe to be called before
* the kernel virtual mapping is activated.
--
2.20.1