On Tue, Aug 2, 2016 at 12:00 PM, Andrey Ryabinin <aryabi...@virtuozzo.com> wrote: > > > On 08/01/2016 05:59 PM, Alexander Potapenko wrote: >> If the total amount of memory assigned to quarantine is less than the >> amount of memory assigned to per-cpu quarantines, |new_quarantine_size| >> may overflow. Instead, set it to zero. >> > > Just curious, how did find this? > Overflow is possible if system has more than 32 cpus per GB of memory. AFIAK > this quite unusual. We were just reading the quarantine code, and Dmitry spotted the problem. I agree this is quite unusual, but we'd better prevent this case.
>> Reported-by: Dmitry Vyukov <dvyu...@google.com> >> Fixes: 55834c59098d ("mm: kasan: initial memory quarantine >> implementation") >> Signed-off-by: Alexander Potapenko <gli...@google.com> >> --- >> mm/kasan/quarantine.c | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c >> index 65793f1..416d3b0 100644 >> --- a/mm/kasan/quarantine.c >> +++ b/mm/kasan/quarantine.c >> @@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, struct >> kmem_cache *cache) >> >> void quarantine_reduce(void) >> { >> - size_t new_quarantine_size; >> + size_t new_quarantine_size, percpu_quarantines; >> unsigned long flags; >> struct qlist_head to_free = QLIST_INIT; >> size_t size_to_free = 0; >> @@ -214,7 +214,15 @@ void quarantine_reduce(void) >> */ >> new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) / >> QUARANTINE_FRACTION; >> - new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus(); >> + percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus(); >> + if (new_quarantine_size < percpu_quarantines) { >> + WARN_ONCE(1, >> + "Too little memory, disabling global KASAN >> quarantine.\n", >> + ); > > Why WARN? I'd suggest pr_warn_once(); Agreed. I'll send the updated patch. (Sorry, Andrew, I'll have to get back to the non-tidy version then, as pr_warn_once() doesn't return the predicate value) >> + new_quarantine_size = 0; >> + } else { >> + new_quarantine_size -= percpu_quarantines; >> + } >> WRITE_ONCE(quarantine_size, new_quarantine_size); >> >> last = global_quarantine.head; >> -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg