From: "Chatradhi, Naveen Krishna" <NaveenKrishna.Chatradhi@amd.com>
To: Guenter Roeck <linux@roeck-us.net>, Jean Delvare <jdelvare@suse.de>
Cc: Hardware Monitoring <linux-hwmon@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: RE: [PATCH v2 2/2] hwmon: (amd_energy) Restore visibility of energy counters
Date: Mon, 19 Apr 2021 16:29:59 +0000 [thread overview]
Message-ID: <DM6PR12MB43888DFB5A7FD52DE4D4433DE8499@DM6PR12MB4388.namprd12.prod.outlook.com> (raw)
In-Reply-To: <797392a6-2d45-2755-7de6-b58ed26c5a50@roeck-us.net>
[AMD Official Use Only - Internal Distribution Only]
Hi Guenter,
>> accum->prev_value = input;
>> + accum->cache_timeout = jiffies + HZ + get_random_int() % HZ;
I've noticed this change is reviewed and accepted, please note “AMD guidance remains to restrict the RAPL MSR access to privilege users for the CVE-2020-12912. See 2020 tab in https://www.amd.com/en/corporate/product-security#paragraph-313561”
Regards,
Naveenk
-----Original Message-----
From: Guenter Roeck <groeck7@gmail.com> On Behalf Of Guenter Roeck
Sent: Monday, April 12, 2021 7:56 PM
To: Jean Delvare <jdelvare@suse.de>
Cc: Hardware Monitoring <linux-hwmon@vger.kernel.org>; Chatradhi, Naveen Krishna <NaveenKrishna.Chatradhi@amd.com>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v2 2/2] hwmon: (amd_energy) Restore visibility of energy counters
[CAUTION: External Email]
On 4/12/21 5:27 AM, Jean Delvare wrote:
> On Fri, 9 Apr 2021 10:48:52 -0700, Guenter Roeck wrote:
>> Commit 60268b0e8258 ("hwmon: (amd_energy) modify the visibility of
>> the counters") restricted visibility of AMD energy counters to work
>> around a side-channel attack using energy data to determine which
>> instructions are executed. The attack is described in 'PLATYPUS:
>> Software-based Power Side-Channel Attacks on x86'. It relies on quick
>> and accurate energy readings.
>>
>> Limiting energy readings to privileged users is annoying. A much
>> better solution is to make energy readings unusable for attacks by
>> randomizing the time between updates. We can do that by caching
>> energy values for a short and randomized period of time.
>>
>> Cc: Naveen Krishna Chatradhi <nchatrad@amd.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> ---
>> v2: Simplified code by using unified function to accumulate energy
>> data
>>
>> drivers/hwmon/amd_energy.c | 29 +++++++++++++++++++++--------
>> 1 file changed, 21 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/hwmon/amd_energy.c b/drivers/hwmon/amd_energy.c
>> index 93bad64039f1..1bf0afc2740c 100644
>> --- a/drivers/hwmon/amd_energy.c
>> +++ b/drivers/hwmon/amd_energy.c
>> @@ -18,6 +18,7 @@
>> #include <linux/mutex.h>
>> #include <linux/processor.h>
>> #include <linux/platform_device.h>
>> +#include <linux/random.h>
>> #include <linux/sched.h>
>> #include <linux/slab.h>
>> #include <linux/topology.h>
>> @@ -35,6 +36,7 @@
>> struct sensor_accumulator {
>> u64 energy_ctr;
>> u64 prev_value;
>> + unsigned long cache_timeout;
>> };
>>
>> struct amd_energy_data {
>> @@ -74,17 +76,14 @@ static void get_energy_units(struct amd_energy_data *data)
>> data->energy_units = (rapl_units & AMD_ENERGY_UNIT_MASK) >> 8;
>> }
>>
>
> Add a comment stating that this function must be called with accum's
> &data->lock held?
>
>> -static void accumulate_delta(struct amd_energy_data *data,
>> - int channel, int cpu, u32 reg)
>> +static void __accumulate_delta(struct sensor_accumulator *accum,
>> + int cpu, u32 reg)
>> {
>> - struct sensor_accumulator *accum;
>> u64 input;
>>
>> - mutex_lock(&data->lock);
>> rdmsrl_safe_on_cpu(cpu, reg, &input);
>> input &= AMD_ENERGY_MASK;
>>
>> - accum = &data->accums[channel];
>> if (input >= accum->prev_value)
>> accum->energy_ctr +=
>> input - accum->prev_value; @@ -93,6 +92,14 @@
>> static void accumulate_delta(struct amd_energy_data *data,
>> accum->prev_value + input;
>>
>> accum->prev_value = input;
>> + accum->cache_timeout = jiffies + HZ + get_random_int() % HZ;
>
> Needs #include <linux/jiffies.h> maybe?
>
>> +}
>> +
>> +static void accumulate_delta(struct amd_energy_data *data,
>> + int channel, int cpu, u32 reg) {
>> + mutex_lock(&data->lock);
>> + __accumulate_delta(&data->accums[channel], cpu, reg);
>> mutex_unlock(&data->lock);
>> }
>>
>> @@ -124,6 +131,7 @@ static int amd_energy_read(struct device *dev, {
>> struct amd_energy_data *data = dev_get_drvdata(dev);
>> struct sensor_accumulator *accum;
>> + u64 energy;
>> u32 reg;
>> int cpu;
>>
>> @@ -140,10 +148,15 @@ static int amd_energy_read(struct device *dev,
>> reg = ENERGY_CORE_MSR;
>> }
>>
>> - accumulate_delta(data, channel, cpu, reg);
>> accum = &data->accums[channel];
>>
>> - *val = div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_units));
>> + mutex_lock(&data->lock);
>> + if (!accum->energy_ctr || time_after(jiffies, accum->cache_timeout))
>> + __accumulate_delta(accum, cpu, reg);
>> + energy = accum->energy_ctr;
>> + mutex_unlock(&data->lock);
>> +
>> + *val = div64_ul(energy * 1000000UL, BIT(data->energy_units));
>>
>> return 0;
>> }
>> @@ -152,7 +165,7 @@ static umode_t amd_energy_is_visible(const void *_data,
>> enum hwmon_sensor_types type,
>> u32 attr, int channel) {
>> - return 0440;
>> + return 0444;
>> }
>>
>> static int energy_accumulator(void *p)
>
> Very nice. This will make the driver useful again :-)
>
> Reviewed-by: Jean Delvare <jdelvare@suse.de>
>
I made the suggested changes.
Thanks a lot for the review!
Guenter
next prev parent reply other threads:[~2021-04-19 16:30 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-09 17:48 [PATCH v2 1/2] hwmon: (amd_energy) Use unified function to read energy data Guenter Roeck
2021-04-09 17:48 ` [PATCH v2 2/2] hwmon: (amd_energy) Restore visibility of energy counters Guenter Roeck
2021-04-12 12:27 ` Jean Delvare
2021-04-12 14:25 ` Guenter Roeck
2021-04-19 16:29 ` Chatradhi, Naveen Krishna [this message]
2021-04-19 17:41 ` Guenter Roeck
2021-04-12 12:14 ` [PATCH v2 1/2] hwmon: (amd_energy) Use unified function to read energy data Jean Delvare
2021-04-12 14:17 ` Guenter Roeck
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