1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _ASM_SCS_H 3 #define _ASM_SCS_H 4 5 #ifdef __ASSEMBLY__ 6 7 #include <asm/asm-offsets.h> 8 #include <asm/sysreg.h> 9 10 #ifdef CONFIG_SHADOW_CALL_STACK 11 scs_sp .req x18 12 13 .macro scs_load_current 14 get_current_task scs_sp 15 ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP] 16 .endm 17 18 .macro scs_save tsk 19 str scs_sp, [\tsk, #TSK_TI_SCS_SP] 20 .endm 21 #else 22 .macro scs_load_current 23 .endm 24 25 .macro scs_save tsk 26 .endm 27 #endif /* CONFIG_SHADOW_CALL_STACK */ 28 29 30 #else 31 32 #include <linux/scs.h> 33 #include <asm/cpufeature.h> 34 35 #ifdef CONFIG_UNWIND_PATCH_PAC_INTO_SCS 36 static inline bool should_patch_pac_into_scs(void) 37 { 38 u64 reg; 39 40 /* 41 * We only enable the shadow call stack dynamically if we are running 42 * on a system that does not implement PAC or BTI. PAC and SCS provide 43 * roughly the same level of protection, and BTI relies on the PACIASP 44 * instructions serving as landing pads, preventing us from patching 45 * those instructions into something else. 46 */ 47 reg = read_sysreg_s(SYS_ID_AA64ISAR1_EL1); 48 if (SYS_FIELD_GET(ID_AA64ISAR1_EL1, APA, reg) | 49 SYS_FIELD_GET(ID_AA64ISAR1_EL1, API, reg)) 50 return false; 51 52 reg = read_sysreg_s(SYS_ID_AA64ISAR2_EL1); 53 if (SYS_FIELD_GET(ID_AA64ISAR2_EL1, APA3, reg)) 54 return false; 55 56 if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)) { 57 reg = read_sysreg_s(SYS_ID_AA64PFR1_EL1); 58 if (reg & (0xf << ID_AA64PFR1_EL1_BT_SHIFT)) 59 return false; 60 } 61 return true; 62 } 63 64 static inline void dynamic_scs_init(void) 65 { 66 if (should_patch_pac_into_scs()) { 67 pr_info("Enabling dynamic shadow call stack\n"); 68 static_branch_enable(&dynamic_scs_enabled); 69 } 70 } 71 #else 72 static inline void dynamic_scs_init(void) {} 73 #endif 74 75 int scs_patch(const u8 eh_frame[], int size); 76 77 #endif /* __ASSEMBLY __ */ 78 79 #endif /* _ASM_SCS_H */ 80