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ARM: spectre-v2: per-CPU vtables to work around big.Little systems

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In big.Little systems, some CPUs require the Spectre workarounds in
paths such as the context switch, but other CPUs do not.  In order
to handle these differences, we need per-CPU vtables.

We are unable to use the kernel's per-CPU variables to support this
as per-CPU is not initialised at times when we need access to the
vtables, so we have to use an array indexed by logical CPU number.

We use an array-of-pointers to avoid having function pointers in
the kernel's read/write .data section.

Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Russell King 2018-07-19 12:21:31 +01:00
parent e209950fdd
commit 383fb3ee80
4 changed files with 61 additions and 15 deletions
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23
arch/arm/include/asm/proc-fns.h
View File

@ -104,12 +104,35 @@ extern void cpu_do_resume(void *);
#else
extern struct processor processor;
#if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
#include <linux/smp.h>
/*
* This can't be a per-cpu variable because we need to access it before
* per-cpu has been initialised. We have a couple of functions that are
* called in a pre-emptible context, and so can't use smp_processor_id()
* there, hence PROC_TABLE(). We insist in init_proc_vtable() that the
* function pointers for these are identical across all CPUs.
*/
extern struct processor *cpu_vtable[];
#define PROC_VTABLE(f) cpu_vtable[smp_processor_id()]->f
#define PROC_TABLE(f) cpu_vtable[0]->f
static inline void init_proc_vtable(const struct processor *p)
{
unsigned int cpu = smp_processor_id();
*cpu_vtable[cpu] = *p;
WARN_ON_ONCE(cpu_vtable[cpu]->dcache_clean_area !=
cpu_vtable[0]->dcache_clean_area);
WARN_ON_ONCE(cpu_vtable[cpu]->set_pte_ext !=
cpu_vtable[0]->set_pte_ext);
}
#else
#define PROC_VTABLE(f) processor.f
#define PROC_TABLE(f) processor.f
static inline void init_proc_vtable(const struct processor *p)
{
processor = *p;
}
#endif
#define cpu_proc_init PROC_VTABLE(_proc_init)
#define cpu_check_bugs PROC_VTABLE(check_bugs)

5
arch/arm/kernel/setup.c
View File

@ -115,6 +115,11 @@ EXPORT_SYMBOL(elf_hwcap2);
#ifdef MULTI_CPU
struct processor processor __ro_after_init;
#if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
struct processor *cpu_vtable[NR_CPUS] = {
[0] = &processor,
};
#endif
#endif
#ifdef MULTI_TLB
struct cpu_tlb_fns cpu_tlb __ro_after_init;

31
arch/arm/kernel/smp.c
View File

@ -42,6 +42,7 @@
#include <asm/mmu_context.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/procinfo.h>
#include <asm/processor.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
@ -102,6 +103,30 @@ static unsigned long get_arch_pgd(pgd_t *pgd)
#endif
}
#if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
static int secondary_biglittle_prepare(unsigned int cpu)
{
if (!cpu_vtable[cpu])
cpu_vtable[cpu] = kzalloc(sizeof(*cpu_vtable[cpu]), GFP_KERNEL);
return cpu_vtable[cpu] ? 0 : -ENOMEM;
}
static void secondary_biglittle_init(void)
{
init_proc_vtable(lookup_processor(read_cpuid_id())->proc);
}
#else
static int secondary_biglittle_prepare(unsigned int cpu)
{
return 0;
}
static void secondary_biglittle_init(void)
{
}
#endif
int __cpu_up(unsigned int cpu, struct task_struct *idle)
{
int ret;
@ -109,6 +134,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
if (!smp_ops.smp_boot_secondary)
return -ENOSYS;
ret = secondary_biglittle_prepare(cpu);
if (ret)
return ret;
/*
* We need to tell the secondary core where to find
* its stack and the page tables.
@ -360,6 +389,8 @@ asmlinkage void secondary_start_kernel(void)
struct mm_struct *mm = &init_mm;
unsigned int cpu;
secondary_biglittle_init();
/*
* The identity mapping is uncached (strongly ordered), so
* switch away from it before attempting any exclusive accesses.

17
arch/arm/mm/proc-v7-bugs.c
View File

@ -52,8 +52,6 @@ static void cpu_v7_spectre_init(void)
case ARM_CPU_PART_CORTEX_A17:
case ARM_CPU_PART_CORTEX_A73:
case ARM_CPU_PART_CORTEX_A75:
if (processor.switch_mm != cpu_v7_bpiall_switch_mm)
goto bl_error;
per_cpu(harden_branch_predictor_fn, cpu) =
harden_branch_predictor_bpiall;
spectre_v2_method = "BPIALL";
@ -61,8 +59,6 @@ static void cpu_v7_spectre_init(void)
case ARM_CPU_PART_CORTEX_A15:
case ARM_CPU_PART_BRAHMA_B15:
if (processor.switch_mm != cpu_v7_iciallu_switch_mm)
goto bl_error;
per_cpu(harden_branch_predictor_fn, cpu) =
harden_branch_predictor_iciallu;
spectre_v2_method = "ICIALLU";
@ -88,11 +84,9 @@ static void cpu_v7_spectre_init(void)
ARM_SMCCC_ARCH_WORKAROUND_1, &res);
if ((int)res.a0 != 0)
break;
if (processor.switch_mm != cpu_v7_hvc_switch_mm && cpu)
goto bl_error;
per_cpu(harden_branch_predictor_fn, cpu) =
call_hvc_arch_workaround_1;
processor.switch_mm = cpu_v7_hvc_switch_mm;
cpu_do_switch_mm = cpu_v7_hvc_switch_mm;
spectre_v2_method = "hypervisor";
break;
@ -101,11 +95,9 @@ static void cpu_v7_spectre_init(void)
ARM_SMCCC_ARCH_WORKAROUND_1, &res);
if ((int)res.a0 != 0)
break;
if (processor.switch_mm != cpu_v7_smc_switch_mm && cpu)
goto bl_error;
per_cpu(harden_branch_predictor_fn, cpu) =
call_smc_arch_workaround_1;
processor.switch_mm = cpu_v7_smc_switch_mm;
cpu_do_switch_mm = cpu_v7_smc_switch_mm;
spectre_v2_method = "firmware";
break;
@ -119,11 +111,6 @@ static void cpu_v7_spectre_init(void)
if (spectre_v2_method)
pr_info("CPU%u: Spectre v2: using %s workaround\n",
smp_processor_id(), spectre_v2_method);
return;
bl_error:
pr_err("CPU%u: Spectre v2: incorrect context switching function, system vulnerable\n",
cpu);
}
#else
static void cpu_v7_spectre_init(void)