linux-kernel - Re: [PATCH 1/2] perf ioctl: Add check for the sample

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Date:   Tue, 28 May 2019 19:50:37 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     jolsa@...hat.com, maddy@...ux.vnet.ibm.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH 1/2] perf ioctl: Add check for the sample_period value

Ravi Bangoria <ravi.bangoria@...ux.ibm.com> writes:
> On 5/13/19 2:26 PM, Peter Zijlstra wrote:
>> On Mon, May 13, 2019 at 09:42:13AM +0200, Peter Zijlstra wrote:
>>> On Sat, May 11, 2019 at 08:12:16AM +0530, Ravi Bangoria wrote:
>>>> Add a check for sample_period value sent from userspace. Negative
>>>> value does not make sense. And in powerpc arch code this could cause
>>>> a recursive PMI leading to a hang (reported when running perf-fuzzer).
>>>>
>>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
>>>> ---
>>>>  kernel/events/core.c | 3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>>> index abbd4b3b96c2..e44c90378940 100644
>>>> --- a/kernel/events/core.c
>>>> +++ b/kernel/events/core.c
>>>> @@ -5005,6 +5005,9 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
>>>>  	if (perf_event_check_period(event, value))
>>>>  		return -EINVAL;
>>>>  
>>>> +	if (!event->attr.freq && (value & (1ULL << 63)))
>>>> +		return -EINVAL;
>>>
>>> Well, perf_event_attr::sample_period is __u64. Would not be the site
>>> using it as signed be the one in error?
>> 
>> You forgot to mention commit: 0819b2e30ccb9, so I guess this just makes
>> it consistent and is fine.
>> 
>
> Yeah, I was about to reply :)

I've taken patch 2. You should probably do a v2 of patch 1 with an
updated change log that explains things fully?

cheers