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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>
This commit is contained in:
Will Deacon 2018-08-07 13:47:06 +01:00 committed by Catalin Marinas
parent 0bf0f444b2
commit 8f04e8e6e2
8 changed files with 106 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
arch/arm64/include/asm/processor.h
View File

@ -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

1
arch/arm64/include/asm/ptrace.h
View File

@ -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

3
arch/arm64/include/asm/sysreg.h
View File

@ -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)

1
arch/arm64/include/uapi/asm/ptrace.h
View File

@ -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

26
arch/arm64/kernel/cpu_errata.c
View File

@ -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 */

45
arch/arm64/kernel/cpufeature.c
View File

@ -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
{},
};

4
arch/arm64/kernel/process.c
View File

@ -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;
}

21
arch/arm64/kernel/ssbd.c
View File

@ -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;