arm64: asm: Override SYM_FUNC_START when building the kernel with BTI

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>
Link: https://lore.kernel.org/r/20200506195138.22086-4-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index ebee3113a62ff7bbc17e12f8de318e9db37caac3..b5a7998a6b2a153eb6dda19be976b00be25c91c0 100644 (file)
--- 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.