Messages in this thread Patches in this message | | | Date | Fri, 20 Apr 2018 14:00:44 +0200 | From | Peter Zijlstra <> | Subject | Re: Smatch check for Spectre stuff |
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Hi Dan,
awesome stuff...
So I fear that many are actually things we want to fix. Our policy was to kill the speculation on the first load and not worry if it can be completed with a dependent load/store.
Also, many of the reported things (for the ones I looked at) are on slow paths and fixing them is a no brainer.
Let me go write Changelogs for the onces I pasted below.
On Thu, Apr 19, 2018 at 08:15:10AM +0300, Dan Carpenter wrote:
> kernel/events/ring_buffer.c:871 perf_mmap_to_page() warn: potential spectre issue 'rb->aux_pages'
That one looks legit.
--- kernel/events/ring_buffer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 6c6b3c48db71..709458b2b839 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -867,8 +867,10 @@ perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) return NULL; /* AUX space */ - if (pgoff >= rb->aux_pgoff) - return virt_to_page(rb->aux_pages[pgoff - rb->aux_pgoff]); + if (pgoff >= rb->aux_pgoff) { + int aux_pgoff = array_index_nospec(pgoff - rb->aux_pgoff, rb->aux_nr_pages); + return virt_to_page(rb->aux_pages[aux_pgoff]); + } } return __perf_mmap_to_page(rb, pgoff); > arch/x86/events/core.c:319 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_event_ids[cache_type]' (local cap) > arch/x86/events/core.c:319 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_event_ids' (local cap) > arch/x86/events/core.c:328 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_extra_regs[cache_type]' (local cap) > arch/x86/events/core.c:328 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_extra_regs' (local cap)
These are legit. At first I figured they'd be of limited exploitablility because we already mask them to 0xFF, but given its a 3 dimensional array, the highest order term can go quite far.
Also, its a slow path. So we should probably fix this.
--- arch/x86/events/core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 7a987e6c7c35..b1a1b19b9a4f 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -304,17 +304,20 @@ set_ext_hw_attr(struct hw_perf_event *hwc, struct perf_event *event) config = attr->config; - cache_type = (config >> 0) & 0xff; + cache_type = (config >> 0) & 0xff; if (cache_type >= PERF_COUNT_HW_CACHE_MAX) return -EINVAL; + cache_type = array_index_nospec(cache_type, PERF_COUNT_HW_CACHE_MAX); cache_op = (config >> 8) & 0xff; if (cache_op >= PERF_COUNT_HW_CACHE_OP_MAX) return -EINVAL; + cache_op = array_index_nospec(cache_op, PERF_COUNT_HW_CACHE_OP_MAX); cache_result = (config >> 16) & 0xff; if (cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX) return -EINVAL; + cache_result = array_index_nospec(cache_result, PERF_COUNT_HW_CACHE_RESULT_MAX); val = hw_cache_event_ids[cache_type][cache_op][cache_result];
> arch/x86/events/intel/cstate.c:307 cstate_pmu_event_init() warn: potential spectre issue 'pkg_msr' (local cap) > arch/x86/events/intel/core.c:337 intel_pmu_event_map() warn: potential spectre issue 'intel_perfmon_event_map' > arch/x86/events/intel/knc.c:122 knc_pmu_event_map() warn: potential spectre issue 'knc_perfmon_event_map' > arch/x86/events/intel/p4.c:722 p4_pmu_event_map() warn: potential spectre issue 'p4_general_events' > arch/x86/events/intel/p6.c:116 p6_pmu_event_map() warn: potential spectre issue 'p6_perfmon_event_map' > arch/x86/events/amd/core.c:132 amd_pmu_event_map() warn: potential spectre issue 'amd_perfmon_event_map'
They also look legit.
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 7a987e6c7c35..e1972f96d043 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -421,6 +424,8 @@ int x86_setup_perfctr(struct perf_event *event) if (attr->config >= x86_pmu.max_events) return -EINVAL; + attr->config = array_index_nospec(attr->config, x86_pmu.max_events); + /* * The generic map: */
> arch/x86/events/msr.c:178 msr_event_init() warn: potential spectre issue 'msr' (local cap)
arch/x86/events/msr.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/x86/events/msr.c b/arch/x86/events/msr.c index e7edf19e64c2..6dcdce729b1f 100644 --- a/arch/x86/events/msr.c +++ b/arch/x86/events/msr.c @@ -158,9 +158,6 @@ static int msr_event_init(struct perf_event *event) if (event->attr.type != event->pmu->type) return -ENOENT; - if (cfg >= PERF_MSR_EVENT_MAX) - return -EINVAL; - /* unsupported modes and filters */ if (event->attr.exclude_user || event->attr.exclude_kernel || @@ -171,6 +168,11 @@ static int msr_event_init(struct perf_event *event) event->attr.sample_period) /* no sampling */ return -EINVAL; + if (cfg >= PERF_MSR_EVENT_MAX) + return -EINVAL; + + cfg = array_index_nospec(cfg, PERF_MSR_EVENT_MAX); + if (!msr[cfg].attr) return -EINVAL; > kernel/sched/core.c:6921 cpu_weight_nice_write_s64() warn: potential spectre issue 'sched_prio_to_weight' again, looks like we want to fix that.
kernel/sched/core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 5e10aaeebfcc..b5d1dfc8f71a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6928,11 +6928,14 @@ static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, s64 nice) { unsigned long weight; + int idx; if (nice < MIN_NICE || nice > MAX_NICE) return -ERANGE; - weight = sched_prio_to_weight[NICE_TO_PRIO(nice) - MAX_RT_PRIO]; + idx = array_index_nospec(NICE_TO_PRIO(nice) - MAX_RT_PRIO, 40); + weight = sched_prio_to_weight[idx]; + return sched_group_set_shares(css_tg(css), scale_load(weight)); } #endif > kernel/sched/autogroup.c:230 proc_sched_autogroup_set_nice() warn: potential spectre issue 'sched_prio_to_weight'
kernel/sched/autogroup.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/sched/autogroup.c b/kernel/sched/autogroup.c index 6be6c575b6cd..9459fe57af4c 100644 --- a/kernel/sched/autogroup.c +++ b/kernel/sched/autogroup.c @@ -209,7 +209,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int nice) static unsigned long next = INITIAL_JIFFIES; struct autogroup *ag; unsigned long shares; - int err; + int err, idx; if (nice < MIN_NICE || nice > MAX_NICE) return -EINVAL; @@ -227,7 +227,9 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int nice) next = HZ / 10 + jiffies; ag = autogroup_task_get(p); - shares = scale_load(sched_prio_to_weight[nice + 20]); + + idx = array_index_nospec(nice + 20, 40); + shares = scale_load(sched_prio_to_weight[idx]); down_write(&ag->lock); err = sched_group_set_shares(ag->tg, shares);
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