linux-kernel - Re: [PATCH v2] perf ioctl: Add check for the sample

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Date:   Tue, 18 Jun 2019 22:28:19 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>, 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 v2] perf ioctl: Add check for the sample_period value

Ravi Bangoria <ravi.bangoria@...ux.ibm.com> writes:
> Peter / mpe,
>
> Is the v2 looks good? If so, can anyone of you please pick this up.

I usually wouldn't take it, it's generic perf code. Unless
peter/ingo/acme tell me otherwise.

It's sort of a bug fix for 0819b2e30ccb, should it have a fixes and/or
stable tag?

  Fixes: 0819b2e30ccb ("perf: Limit perf_event_attr::sample_period to 63 bits")
  Cc: stable@...r.kernel.org # v3.15+

cheers

> On 6/4/19 9:59 AM, Ravi Bangoria wrote:
>> perf_event_open() limits the sample_period to 63 bits. See
>> commit 0819b2e30ccb ("perf: Limit perf_event_attr::sample_period
>> to 63 bits"). Make ioctl() consistent with it.
>> 
>> Also on powerpc, negative sample_period could cause a recursive
>> PMIs 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;
>> +
>>  	event_function_call(event, __perf_event_period, &value);
>>  
>>  	return 0;
>>