Merge branch 'for-next/dynamic-scs' into for-next/core

* for-next/dynamic-scs:
  arm64: implement dynamic shadow call stack for Clang
  scs: add support for dynamic shadow call stacks
  arm64: unwind: add asynchronous unwind tables to kernel and modules

2 files changed, 57 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index 094701ec5500..dbba4b7559aa 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -17,4 +17,12 @@ SECTIONS {
 	 */
 	.text.hot : { *(.text.hot) }
 #endif
+
+#ifdef CONFIG_UNWIND_TABLES
+	/*
+	 * Currently, we only use unwind info at module load time, so we can
+	 * put it into the .init allocation.
+	 */
+	.init.eh_frame : { *(.eh_frame) }
+#endif
 }
diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
index 8297bccf0784..ff7da1268a52 100644
--- a/arch/arm64/include/asm/scs.h
+++ b/arch/arm64/include/asm/scs.h
@@ -5,6 +5,7 @@
 #ifdef __ASSEMBLY__
 
 #include <asm/asm-offsets.h>
+#include <asm/sysreg.h>
 
 #ifdef CONFIG_SHADOW_CALL_STACK
 	scs_sp	.req	x18
@@ -24,6 +25,54 @@
 	.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);
+
 #endif /* __ASSEMBLY __ */
 
 #endif /* _ASM_SCS_H */