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SubjectRe: Smatch check for Spectre stuff

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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