On Mon, Jul 4, 2016 at 8:11 PM, Andrey Ryabinin <ryabinin....@gmail.com> wrote:
> 2016-07-01 20:38 GMT+03:00 Dmitry Vyukov <dvyu...@google.com>:
>> I've hit a GPF in depot_fetch_stack when it was given
>> bogus stack handle. I think it was caused by a distant
>> out-of-bounds that hit a different object, as the result
>> we treated uninit garbage as stack handle. Maybe there is
>> something to fix in KASAN logic, but I think it makes
>> sense to make depot_fetch_stack more robust as well.
>>
>> Verify that the provided stack handle looks correct.
>>
> I don't think that adding the kernel code to work around bugs in the
> kernel code makes a lot of sense.
> depot_fetch_stack() fails if invalid handler is passed, and that is a
> bug. You can just add WARN_ON() in
> depot_fetch_stack() if you want to detect such cases..
In this case, the code happens to be a debugging tool that actively anticipates
bad memory accesses. If the tool can reliably detect bad input that could
potentially cause a crash inside the debugger itself, and take actions
to prevent it,
I believe that's a good thing.
> Note that KASAN detects corruption of object's metadata, so such check
> may help only in case of
> corruption page owner's data.
It will also help in case of bad access by non-instrumented code.
>
>> if (page_ext->last_migrate_reason != -1) {
>> ret += snprintf(kbuf + ret, count - ret,
>> @@ -307,12 +308,11 @@ void __dump_page_owner(struct page *page)
>> }
>>
>> handle = READ_ONCE(page_ext->handle);
>> - if (!handle) {
>> + if (!depot_fetch_stack(handle, &trace)) {
>> pr_alert("page_owner info is not active (free page?)\n");
>> return;
>> }
>>
>> - depot_fetch_stack(handle, &trace);
>> pr_alert("page allocated via order %u, migratetype %s, gfp_mask
>> %#x(%pGg)\n",
>> page_ext->order, migratetype_names[mt], gfp_mask,
>> &gfp_mask);
>> print_stack_trace(&trace, 0);
>> --
>> 2.8.0.rc3.226.g39d4020
>>
>
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