arm64: ssbd: Add support for PSTATE.SSBS rather than trapping to EL3

On CPUs with support for PSTATE.SSBS, the kernel can toggle the SSBD
state without needing to call into firmware.

This patch hooks into the existing SSBD infrastructure so that SSBS is
used on CPUs that support it, but it's all made horribly complicated by
the very real possibility of big/little systems that don't uniformly
provide the new capability.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 79657ad..f683537 100644 (file)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -174,6 +174,10 @@ static inline void start_thread(struct pt_regs *regs, unsigned long pc,
 {
        start_thread_common(regs, pc);
        regs->pstate = PSR_MODE_EL0t;
+
+       if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE)
+               regs->pstate |= PSR_SSBS_BIT;
+
        regs->sp = sp;
 }
 
@@ -190,6 +194,9 @@ static inline void compat_start_thread(struct pt_regs *regs, unsigned long pc,
        regs->pstate |= PSR_AA32_E_BIT;
 #endif
 
+       if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE)
+               regs->pstate |= PSR_AA32_SSBS_BIT;
+
        regs->compat_sp = sp;
 }
 #endif

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 177b851..6bc4388 100644 (file)
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -50,6 +50,7 @@
 #define PSR_AA32_I_BIT         0x00000080
 #define PSR_AA32_A_BIT         0x00000100
 #define PSR_AA32_E_BIT         0x00000200
+#define PSR_AA32_SSBS_BIT      0x00800000
 #define PSR_AA32_DIT_BIT       0x01000000
 #define PSR_AA32_Q_BIT         0x08000000
 #define PSR_AA32_V_BIT         0x10000000

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 2fc6242..3091ae5 100644 (file)
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -86,11 +86,14 @@
 
 #define REG_PSTATE_PAN_IMM             sys_reg(0, 0, 4, 0, 4)
 #define REG_PSTATE_UAO_IMM             sys_reg(0, 0, 4, 0, 3)
+#define REG_PSTATE_SSBS_IMM            sys_reg(0, 3, 4, 0, 1)
 
 #define SET_PSTATE_PAN(x) __emit_inst(0xd5000000 | REG_PSTATE_PAN_IMM |        \
                                      (!!x)<<8 | 0x1f)
 #define SET_PSTATE_UAO(x) __emit_inst(0xd5000000 | REG_PSTATE_UAO_IMM |        \
                                      (!!x)<<8 | 0x1f)
+#define SET_PSTATE_SSBS(x) __emit_inst(0xd5000000 | REG_PSTATE_SSBS_IMM | \
+                                      (!!x)<<8 | 0x1f)
 
 #define SYS_DC_ISW                     sys_insn(1, 0, 7, 6, 2)
 #define SYS_DC_CSW                     sys_insn(1, 0, 7, 10, 2)

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 98c4ce5..a36227f 100644 (file)
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -46,6 +46,7 @@
 #define PSR_I_BIT      0x00000080
 #define PSR_A_BIT      0x00000100
 #define PSR_D_BIT      0x00000200
+#define PSR_SSBS_BIT   0x00001000
 #define PSR_PAN_BIT    0x00400000
 #define PSR_UAO_BIT    0x00800000
 #define PSR_V_BIT      0x10000000

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index dec1089..c063490 100644 (file)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -312,6 +312,14 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt,
 
 void arm64_set_ssbd_mitigation(bool state)
 {
+       if (this_cpu_has_cap(ARM64_SSBS)) {
+               if (state)
+                       asm volatile(SET_PSTATE_SSBS(0));
+               else
+                       asm volatile(SET_PSTATE_SSBS(1));
+               return;
+       }
+
        switch (psci_ops.conduit) {
        case PSCI_CONDUIT_HVC:
                arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_2, state, NULL);
@@ -336,6 +344,11 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
 
        WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
 
+       if (this_cpu_has_cap(ARM64_SSBS)) {
+               required = false;
+               goto out_printmsg;
+       }
+
        if (psci_ops.smccc_version == SMCCC_VERSION_1_0) {
                ssbd_state = ARM64_SSBD_UNKNOWN;
                return false;
@@ -384,7 +397,6 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
 
        switch (ssbd_state) {
        case ARM64_SSBD_FORCE_DISABLE:
-               pr_info_once("%s disabled from command-line\n", entry->desc);
                arm64_set_ssbd_mitigation(false);
                required = false;
                break;
@@ -397,7 +409,6 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
                break;
 
        case ARM64_SSBD_FORCE_ENABLE:
-               pr_info_once("%s forced from command-line\n", entry->desc);
                arm64_set_ssbd_mitigation(true);
                required = true;
                break;
@@ -407,6 +418,17 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
                break;
        }
 
+out_printmsg:
+       switch (ssbd_state) {
+       case ARM64_SSBD_FORCE_DISABLE:
+               pr_info_once("%s disabled from command-line\n", entry->desc);
+               break;
+
+       case ARM64_SSBD_FORCE_ENABLE:
+               pr_info_once("%s forced from command-line\n", entry->desc);
+               break;
+       }
+
        return required;
 }
 #endif /* CONFIG_ARM64_SSBD */

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5794959..9aa18a0 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1039,6 +1039,48 @@ static void cpu_has_fwb(const struct arm64_cpu_capabilities *__unused)
        WARN_ON(val & (7 << 27 | 7 << 21));
 }
 
+#ifdef CONFIG_ARM64_SSBD
+static int ssbs_emulation_handler(struct pt_regs *regs, u32 instr)
+{
+       if (user_mode(regs))
+               return 1;
+
+       if (instr & BIT(CRm_shift))
+               regs->pstate |= PSR_SSBS_BIT;
+       else
+               regs->pstate &= ~PSR_SSBS_BIT;
+
+       arm64_skip_faulting_instruction(regs, 4);
+       return 0;
+}
+
+static struct undef_hook ssbs_emulation_hook = {
+       .instr_mask     = ~(1U << CRm_shift),
+       .instr_val      = 0xd500001f | REG_PSTATE_SSBS_IMM,
+       .fn             = ssbs_emulation_handler,
+};
+
+static void cpu_enable_ssbs(const struct arm64_cpu_capabilities *__unused)
+{
+       static bool undef_hook_registered = false;
+       static DEFINE_SPINLOCK(hook_lock);
+
+       spin_lock(&hook_lock);
+       if (!undef_hook_registered) {
+               register_undef_hook(&ssbs_emulation_hook);
+               undef_hook_registered = true;
+       }
+       spin_unlock(&hook_lock);
+
+       if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE) {
+               sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_DSSBS);
+               arm64_set_ssbd_mitigation(false);
+       } else {
+               arm64_set_ssbd_mitigation(true);
+       }
+}
+#endif /* CONFIG_ARM64_SSBD */
+
 static const struct arm64_cpu_capabilities arm64_features[] = {
        {
                .desc = "GIC system register CPU interface",
@@ -1226,6 +1268,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
                .cpu_enable = cpu_enable_hw_dbm,
        },
 #endif
+#ifdef CONFIG_ARM64_SSBD
        {
                .desc = "CRC32 instructions",
                .capability = ARM64_HAS_CRC32,
@@ -1244,7 +1287,9 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
                .field_pos = ID_AA64PFR1_SSBS_SHIFT,
                .sign = FTR_UNSIGNED,
                .min_field_value = ID_AA64PFR1_SSBS_PSTATE_ONLY,
+               .cpu_enable = cpu_enable_ssbs,
        },
+#endif
        {},
 };
 

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 7f1628e..ce99c58 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -358,6 +358,10 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
                if (IS_ENABLED(CONFIG_ARM64_UAO) &&
                    cpus_have_const_cap(ARM64_HAS_UAO))
                        childregs->pstate |= PSR_UAO_BIT;
+
+               if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE)
+                       childregs->pstate |= PSR_SSBS_BIT;
+
                p->thread.cpu_context.x19 = stack_start;
                p->thread.cpu_context.x20 = stk_sz;
        }

diff --git a/arch/arm64/kernel/ssbd.c b/arch/arm64/kernel/ssbd.c
index 07b12c0..885f13e 100644 (file)
--- a/arch/arm64/kernel/ssbd.c
+++ b/arch/arm64/kernel/ssbd.c
@@ -3,12 +3,30 @@
  * Copyright (C) 2018 ARM Ltd, All Rights Reserved.
  */
 
+#include <linux/compat.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
+#include <linux/sched/task_stack.h>
 #include <linux/thread_info.h>
 
 #include <asm/cpufeature.h>
 
+static void ssbd_ssbs_enable(struct task_struct *task)
+{
+       u64 val = is_compat_thread(task_thread_info(task)) ?
+                 PSR_AA32_SSBS_BIT : PSR_SSBS_BIT;
+
+       task_pt_regs(task)->pstate |= val;
+}
+
+static void ssbd_ssbs_disable(struct task_struct *task)
+{
+       u64 val = is_compat_thread(task_thread_info(task)) ?
+                 PSR_AA32_SSBS_BIT : PSR_SSBS_BIT;
+
+       task_pt_regs(task)->pstate &= ~val;
+}
+
 /*
  * prctl interface for SSBD
  */
@@ -44,12 +62,14 @@ static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
                        return -EPERM;
                task_clear_spec_ssb_disable(task);
                clear_tsk_thread_flag(task, TIF_SSBD);
+               ssbd_ssbs_enable(task);
                break;
        case PR_SPEC_DISABLE:
                if (state == ARM64_SSBD_FORCE_DISABLE)
                        return -EPERM;
                task_set_spec_ssb_disable(task);
                set_tsk_thread_flag(task, TIF_SSBD);
+               ssbd_ssbs_disable(task);
                break;
        case PR_SPEC_FORCE_DISABLE:
                if (state == ARM64_SSBD_FORCE_DISABLE)
@@ -57,6 +77,7 @@ static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
                task_set_spec_ssb_disable(task);
                task_set_spec_ssb_force_disable(task);
                set_tsk_thread_flag(task, TIF_SSBD);
+               ssbd_ssbs_disable(task);
                break;
        default:
                return -ERANGE;