arch/arm64/include/asm/scs.h

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