Messages in this thread Patch in this message | | | Subject | Re: [PATCH V5] perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task | From | "Liang, Kan" <> | Date | Wed, 21 Apr 2021 11:12:06 -0400 |
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On 4/21/2021 4:11 AM, Peter Zijlstra wrote: >> @@ -2327,10 +2367,17 @@ static void x86_pmu_event_mapped(struct perf_event *event, struct mm_struct *mm) >> >> static void x86_pmu_event_unmapped(struct perf_event *event, struct mm_struct *mm) >> { >> + unsigned long flags; >> >> if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) >> return; >> >> + if (x86_pmu.sched_task && event->hw.target) { >> + local_irq_save(flags); >> + perf_sched_cb_dec(event->ctx->pmu); >> + local_irq_restore(flags); >> + } >> + >> if (atomic_dec_and_test(&mm->context.perf_rdpmc_allowed)) >> on_each_cpu_mask(mm_cpumask(mm), cr4_update_pce, NULL, 1); >> } > I don't understand how this can possibly be correct. Both > perf_sched_cb_{inc,dec} modify strict per-cpu state, but the mapped > functions happen on whatever random CPU of the moment whenever the task > memory map changes. > > Suppose we mmap() on CPU0 and then exit on CPU1. Suppose the task does > mmap() on CPU0 but then creates threads and runs on CPU1-4 concurrently > before existing on CPU5. > > Could be I'm not seeing it due to having a snot-brain, please explain.
You are right. I implemented a new test case which mmap() on CPU 3, run and exit on CPU 0. It can still read the counter values from other tasks on CPU 0.
Actually, I don't think we need perf_sched_cb_{inc,dec} and sched_task().
The mm->context.perf_rdpmc_allowed will tell us if it's a RDPMC task. I think a clean way should be to add a new check_leakage() method. When perf schedules in a RDPMC task, we invoke the method and clear the dirty counters. (I use a generic name check_leakage for the method so it can be reused by other ARCHs if possible.)
The patch is as below. The new and old test cases are all passed. I will do more tests.
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index c7fcc8d..229dd48 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1624,6 +1624,8 @@ static void x86_pmu_del(struct perf_event *event, int flags) if (cpuc->txn_flags & PERF_PMU_TXN_ADD) goto do_del;
+ __set_bit(event->hw.idx, cpuc->dirty); + /* * Not a TXN, therefore cleanup properly. */ @@ -2631,6 +2633,37 @@ static int x86_pmu_check_period(struct perf_event *event, u64 value) return 0; }
+static void x86_pmu_clear_dirty_counters(void) +{ + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); + int i; + + /* Don't need to clear the assigned counter. */ + for (i = 0; i < cpuc->n_events; i++) + __clear_bit(cpuc->assign[i], cpuc->dirty); + + if (bitmap_empty(cpuc->dirty, X86_PMC_IDX_MAX)) + return; + + for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) { + /* Metrics and fake events don't have corresponding HW counters. */ + if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR)) + continue; + else if (i >= INTEL_PMC_IDX_FIXED) + wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + (i - INTEL_PMC_IDX_FIXED), 0); + else + wrmsrl(x86_pmu_event_addr(i), 0); + } + + bitmap_zero(cpuc->dirty, X86_PMC_IDX_MAX); +} + +static void x86_pmu_check_leakage(void) +{ + if (READ_ONCE(x86_pmu.attr_rdpmc)) + x86_pmu_clear_dirty_counters(); +} + static int x86_pmu_aux_output_match(struct perf_event *event) { if (!(pmu.capabilities & PERF_PMU_CAP_AUX_OUTPUT)) @@ -2675,6 +2708,7 @@ static struct pmu pmu = { .sched_task = x86_pmu_sched_task, .swap_task_ctx = x86_pmu_swap_task_ctx, .check_period = x86_pmu_check_period, + .check_leakage = x86_pmu_check_leakage,
.aux_output_match = x86_pmu_aux_output_match,
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h index 27fa85e..d6003e0 100644 --- a/arch/x86/events/perf_event.h +++ b/arch/x86/events/perf_event.h @@ -229,6 +229,7 @@ struct cpu_hw_events { */ struct perf_event *events[X86_PMC_IDX_MAX]; /* in counter order */ unsigned long active_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)]; + unsigned long dirty[BITS_TO_LONGS(X86_PMC_IDX_MAX)]; int enabled;
int n_events; /* the # of events in the below arrays */ diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index a763928..bcf3964 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -514,6 +514,11 @@ struct pmu { * Check period value for PERF_EVENT_IOC_PERIOD ioctl. */ int (*check_period) (struct perf_event *event, u64 value); /* optional */ + + /* + * Check and clear dirty counters to prevent potential leakage + */ + void (*check_leakage) (void); /* optional */ };
enum perf_addr_filter_action_t { diff --git a/kernel/events/core.c b/kernel/events/core.c index 928b166..b496113 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3822,6 +3822,12 @@ static void cpu_ctx_sched_in(struct perf_cpu_context *cpuctx, ctx_sched_in(ctx, cpuctx, event_type, task); }
+static bool has_check_leakage(struct pmu *pmu) +{ + return pmu->check_leakage && current->mm && + atomic_read(¤t->mm->context.perf_rdpmc_allowed); +} + static void perf_event_context_sched_in(struct perf_event_context *ctx, struct task_struct *task) { @@ -3832,6 +3838,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx, if (cpuctx->task_ctx == ctx) { if (cpuctx->sched_cb_usage) __perf_pmu_sched_task(cpuctx, true); + if (has_check_leakage(pmu)) + pmu->check_leakage(); return; }
@@ -3858,6 +3866,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
if (cpuctx->sched_cb_usage && pmu->sched_task) pmu->sched_task(cpuctx->task_ctx, true); + if (has_check_leakage(pmu)) + pmu->check_leakage();
perf_pmu_enable(pmu);
Thanks, Kan
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