From: Will Deacon <will.deacon@xxxxxxx>
[ Upstream commit 8f04e8e6e29c93421a95b61cad62e3918425eac7 ]
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@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/processor.h | 7 +++++
arch/arm64/include/asm/ptrace.h | 1
arch/arm64/include/asm/sysreg.h | 3 ++
arch/arm64/include/uapi/asm/ptrace.h | 1
arch/arm64/kernel/cpu_errata.c | 26 ++++++++++++++++++--
arch/arm64/kernel/cpufeature.c | 45 +++++++++++++++++++++++++++++++++++
arch/arm64/kernel/process.c | 4 +++
arch/arm64/kernel/ssbd.c | 21 ++++++++++++++++
8 files changed, 106 insertions(+), 2 deletions(-)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -182,6 +182,10 @@ static inline void start_thread(struct p
{
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;
}
@@ -198,6 +202,9 @@ static inline void compat_start_thread(s
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
--- 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
--- 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)
--- 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
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -312,6 +312,14 @@ void __init arm64_enable_wa2_handling(st
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 st
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 st
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 st
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 st
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 */
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1071,6 +1071,48 @@ static void cpu_has_fwb(const struct arm
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",
@@ -1258,6 +1300,7 @@ static const struct arm64_cpu_capabiliti
.cpu_enable = cpu_enable_hw_dbm,
},
#endif
+#ifdef CONFIG_ARM64_SSBD
{
.desc = "Speculative Store Bypassing Safe (SSBS)",
.capability = ARM64_SSBS,
@@ -1267,7 +1310,9 @@ static const struct arm64_cpu_capabiliti
.field_pos = ID_AA64PFR1_SSBS_SHIFT,
.sign = FTR_UNSIGNED,
.min_field_value = ID_AA64PFR1_SSBS_PSTATE_ONLY,
+ .cpu_enable = cpu_enable_ssbs,
},
+#endif
{},
};
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -358,6 +358,10 @@ int copy_thread(unsigned long clone_flag
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;
}
--- a/arch/arm64/kernel/ssbd.c
+++ b/arch/arm64/kernel/ssbd.c
@@ -3,13 +3,31 @@
* Copyright (C) 2018 ARM Ltd, All Rights Reserved.
*/
+#include <linux/compat.h>
#include <linux/errno.h>
#include <linux/prctl.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
* FIXME: Drop the below ifdefery once merged in 4.18.
@@ -47,12 +65,14 @@ static int ssbd_prctl_set(struct task_st
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)
@@ -60,6 +80,7 @@ static int ssbd_prctl_set(struct task_st
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;
