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Mon, 12 Apr 2021 07:25:32 -0700 (PDT) Sender: Guenter Roeck Subject: Re: [PATCH v2 2/2] hwmon: (amd_energy) Restore visibility of energy counters To: Jean Delvare Cc: Hardware Monitoring , Naveen Krishna Chatradhi , Greg Kroah-Hartman References: <20210409174852.4585-1-linux@roeck-us.net> <20210409174852.4585-2-linux@roeck-us.net> <20210412142744.54c55d06@endymion> From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= Message-ID: <797392a6-2d45-2755-7de6-b58ed26c5a50@roeck-us.net> Date: Mon, 12 Apr 2021 07:25:31 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210412142744.54c55d06@endymion> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org 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 >> Cc: Greg Kroah-Hartman >> Signed-off-by: Guenter Roeck >> --- >> 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 >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -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 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 > I made the suggested changes. Thanks a lot for the review! Guenter