Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 27 Oct 2014 08:45:01 -0700 | Subject | Re: [PATCH v2 7/8] x86, perf: Only allow rdpmc if a perf_event is mapped |
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On Oct 27, 2014 12:17 AM, "张静(长谷)" <hillf.zj@alibaba-inc.com> wrote: > > > > > We currently allow any process to use rdpmc. This significantly > > weakens the protection offered by PR_TSC_DISABLED, and it could be > > helpful to users attempting to exploit timing attacks. > > > > Since we can't enable access to individual counters, use a very > > coarse heuristic to limit access to rdpmc: allow access only when > > a perf_event is mmapped. This protects seccomp sandboxes. > > > > There is plenty of room to further tighen these restrictions. For > > example, this allows rdpmc for any x86_pmu event, but it's only > > useful for self-monitoring tasks. > > > > As a side effect, cap_user_rdpmc will now be false for AMD uncore > > events. This isn't a real regression, since .event_idx is disabled > > for these events anyway for the time being. Whenever that gets > > re-added, the cap_user_rdpmc code can be adjusted or refactored > > accordingly. > > > > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > > --- > > arch/x86/include/asm/mmu.h | 2 ++ > > arch/x86/include/asm/mmu_context.h | 16 +++++++++++ > > arch/x86/kernel/cpu/perf_event.c | 57 +++++++++++++++++++++++++------------- > > arch/x86/kernel/cpu/perf_event.h | 2 ++ > > 4 files changed, 58 insertions(+), 19 deletions(-) > > > > diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h > > index 876e74e8eec7..09b9620a73b4 100644 > > --- a/arch/x86/include/asm/mmu.h > > +++ b/arch/x86/include/asm/mmu.h > > @@ -19,6 +19,8 @@ typedef struct { > > > > struct mutex lock; > > void __user *vdso; > > + > > + atomic_t perf_rdpmc_allowed; /* nonzero if rdpmc is allowed */ > > } mm_context_t; > > > > #ifdef CONFIG_SMP > > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h > > index 23697f74b372..ccad8d616038 100644 > > --- a/arch/x86/include/asm/mmu_context.h > > +++ b/arch/x86/include/asm/mmu_context.h > > @@ -19,6 +19,18 @@ static inline void paravirt_activate_mm(struct mm_struct *prev, > > } > > #endif /* !CONFIG_PARAVIRT */ > > > > +#ifdef CONFIG_PERF_EVENTS > > +static inline void load_mm_cr4(struct mm_struct *mm) > > +{ > > + if (atomic_read(&mm->context.perf_rdpmc_allowed)) > > + cr4_set_bits(X86_CR4_PCE); > > + else > > + cr4_clear_bits(X86_CR4_PCE); > > +} > > +#else > > +static inline void load_mm_cr4(struct mm_struct *mm) {} > > +#endif > > + > > /* > > * Used for LDT copy/destruction. > > */ > > @@ -53,6 +65,9 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, > > /* Stop flush ipis for the previous mm */ > > cpumask_clear_cpu(cpu, mm_cpumask(prev)); > > > > + /* Load per-mm CR4 state */ > > + load_mm_cr4(next); > > + > > /* > > * Load the LDT, if the LDT is different. > > * > > @@ -88,6 +103,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, > > */ > > load_cr3(next->pgd); > > trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); > > + load_mm_cr4(next); > > load_LDT_nolock(&next->context); > > } > > } > > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > > index 00fbab7aa587..3e875b3b30f2 100644 > > --- a/arch/x86/kernel/cpu/perf_event.c > > +++ b/arch/x86/kernel/cpu/perf_event.c > > @@ -31,6 +31,7 @@ > > #include <asm/nmi.h> > > #include <asm/smp.h> > > #include <asm/alternative.h> > > +#include <asm/mmu_context.h> > > #include <asm/tlbflush.h> > > #include <asm/timer.h> > > #include <asm/desc.h> > > @@ -1336,8 +1337,6 @@ x86_pmu_notifier(struct notifier_block *self, unsigned long action, void *hcpu) > > break; > > > > case CPU_STARTING: > > - if (x86_pmu.attr_rdpmc) > > - cr4_set_bits(X86_CR4_PCE); > > if (x86_pmu.cpu_starting) > > x86_pmu.cpu_starting(cpu); > > break; > > @@ -1813,14 +1812,44 @@ static int x86_pmu_event_init(struct perf_event *event) > > event->destroy(event); > > } > > > > + if (ACCESS_ONCE(x86_pmu.attr_rdpmc)) > > + event->hw.flags |= PERF_X86_EVENT_RDPMC_ALLOWED; > > + > > return err; > > } > > > > +static void refresh_pce(void *ignored) > > +{ > > + if (current->mm) > > + load_mm_cr4(current->mm); > > +} > > + > > +static void x86_pmu_event_mapped(struct perf_event *event) > > +{ > > + if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) > > + return; > > + > > + if (atomic_inc_return(¤t->mm->context.perf_rdpmc_allowed) == 1) > > + on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); > > +} > > + > > +static void x86_pmu_event_unmapped(struct perf_event *event) > > +{ > > + if (!current->mm) > > + return; > > + > > + if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) > > + return; > > + > > + if (atomic_dec_and_test(¤t->mm->context.perf_rdpmc_allowed)) > > + on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); > > The current task(T-a on CPU A) is asking CPUs(A, B, C, D) to refresh pce, and looks > the current task(T-d on CPU D) is disturbed if T-d loaded CR4 when going on CPU D.
I don't understand. This code is intended to interrupt only affected tasks, except for a race if cpus switch mm while this code is running. At worst, the race should only result in an unnecessary IPI.
Can you clarify your concern?
--Andy
> > Hillf > > +} > > + > > static int x86_pmu_event_idx(struct perf_event *event) > > { > > int idx = event->hw.idx; > > > > - if (!x86_pmu.attr_rdpmc) > > + if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) > > return 0; > > > > if (x86_pmu.num_counters_fixed && idx >= INTEL_PMC_IDX_FIXED) { > > @@ -1838,16 +1867,6 @@ static ssize_t get_attr_rdpmc(struct device *cdev, > > return snprintf(buf, 40, "%d\n", x86_pmu.attr_rdpmc); > > } > > > > -static void change_rdpmc(void *info) > > -{ > > - bool enable = !!(unsigned long)info; > > - > > - if (enable) > > - cr4_set_bits(X86_CR4_PCE); > > - else > > - cr4_clear_bits(X86_CR4_PCE); > > -} > > - > > static ssize_t set_attr_rdpmc(struct device *cdev, > > struct device_attribute *attr, > > const char *buf, size_t count) > > @@ -1862,11 +1881,7 @@ static ssize_t set_attr_rdpmc(struct device *cdev, > > if (x86_pmu.attr_rdpmc_broken) > > return -ENOTSUPP; > > > > - if (!!val != !!x86_pmu.attr_rdpmc) { > > - x86_pmu.attr_rdpmc = !!val; > > - on_each_cpu(change_rdpmc, (void *)val, 1); > > - } > > - > > + x86_pmu.attr_rdpmc = !!val; > > return count; > > } > > > > @@ -1909,6 +1924,9 @@ static struct pmu pmu = { > > > > .event_init = x86_pmu_event_init, > > > > + .event_mapped = x86_pmu_event_mapped, > > + .event_unmapped = x86_pmu_event_unmapped, > > + > > .add = x86_pmu_add, > > .del = x86_pmu_del, > > .start = x86_pmu_start, > > @@ -1930,7 +1948,8 @@ void arch_perf_update_userpage(struct perf_event *event, > > > > userpg->cap_user_time = 0; > > userpg->cap_user_time_zero = 0; > > - userpg->cap_user_rdpmc = x86_pmu.attr_rdpmc; > > + userpg->cap_user_rdpmc = > > + !!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED); > > userpg->pmc_width = x86_pmu.cntval_bits; > > > > if (!sched_clock_stable()) > > diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h > > index d98a34d435d7..f6868186e67b 100644 > > --- a/arch/x86/kernel/cpu/perf_event.h > > +++ b/arch/x86/kernel/cpu/perf_event.h > > @@ -71,6 +71,8 @@ struct event_constraint { > > #define PERF_X86_EVENT_COMMITTED 0x8 /* event passed commit_txn */ > > #define PERF_X86_EVENT_PEBS_LD_HSW 0x10 /* haswell style datala, load */ > > #define PERF_X86_EVENT_PEBS_NA_HSW 0x20 /* haswell style datala, unknown */ > > +#define PERF_X86_EVENT_RDPMC_ALLOWED 0x40 /* grant rdpmc permission */ > > + > > > > struct amd_nb { > > int nb_id; /* NorthBridge id */ > > -- > > 1.9.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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