1 files changed, 80 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
new file mode 100644
index 0000000000..3fdae5fe31
--- /dev/null
+++ b/arch/arm64/include/asm/scs.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_SCS_H
+#define _ASM_SCS_H
+
+#ifdef __ASSEMBLY__
+
+#include <asm/asm-offsets.h>
+#include <asm/sysreg.h>
+
+#ifdef CONFIG_SHADOW_CALL_STACK
+	scs_sp	.req	x18
+
+	.macro scs_load_current
+	get_current_task scs_sp
+	ldr	scs_sp, [scs_sp, #TSK_TI_SCS_SP]
+	.endm
+
+	.macro scs_save tsk
+	str	scs_sp, [\tsk, #TSK_TI_SCS_SP]
+	.endm
+#else
+	.macro scs_load_current
+	.endm
+
+	.macro scs_save tsk
+	.endm
+#endif /* CONFIG_SHADOW_CALL_STACK */
+
+
+#else
+
+#include <linux/scs.h>
+#include <asm/cpufeature.h>
+
+#ifdef CONFIG_UNWIND_PATCH_PAC_INTO_SCS
+static inline bool should_patch_pac_into_scs(void)
+{
+	u64 reg;
+
+	/*
+	 * We only enable the shadow call stack dynamically if we are running
+	 * on a system that does not implement PAC or BTI. PAC and SCS provide
+	 * roughly the same level of protection, and BTI relies on the PACIASP
+	 * instructions serving as landing pads, preventing us from patching
+	 * those instructions into something else.
+	 */
+	reg = read_sysreg_s(SYS_ID_AA64ISAR1_EL1);
+	if (SYS_FIELD_GET(ID_AA64ISAR1_EL1, APA, reg) |
+	    SYS_FIELD_GET(ID_AA64ISAR1_EL1, API, reg))
+		return false;
+
+	reg = read_sysreg_s(SYS_ID_AA64ISAR2_EL1);
+	if (SYS_FIELD_GET(ID_AA64ISAR2_EL1, APA3, reg))
+		return false;
+
+	if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)) {
+		reg = read_sysreg_s(SYS_ID_AA64PFR1_EL1);
+		if (reg & (0xf << ID_AA64PFR1_EL1_BT_SHIFT))
+			return false;
+	}
+	return true;
+}
+
+static inline void dynamic_scs_init(void)
+{
+	if (should_patch_pac_into_scs()) {
+		pr_info("Enabling dynamic shadow call stack\n");
+		static_branch_enable(&dynamic_scs_enabled);
+	}
+}
+#else
+static inline void dynamic_scs_init(void) {}
+#endif
+
+int scs_patch(const u8 eh_frame[], int size);
+asmlinkage void scs_patch_vmlinux(void);
+
+#endif /* __ASSEMBLY __ */
+
+#endif /* _ASM_SCS_H */