On Sun, Nov 22, 2020 at 04:42:47PM +0000, Chatradhi, Naveen Krishna wrote: > [AMD Official Use Only - Approved for External Use] > > Hi Guenter, > > > A much better fix would have been to cache RAPL data for a short period of time. To avoid any possibility of attacks, maybe add some random interval. Something like this: > Thanks for the tip, I will check this out. > > > In accumulate_delta(): > > accums->next_update = jiffies + HZ / 2 + get_random_int % HZ; [ and this was supposed to be get_random_int() ] > > > In amd_energy_read(): > > accum = &data->accums[channel]; > > if (time_after(accum->next_update)) > Do you mean if (time_after(jiffies, accum->next_update)) yes ... Guenter > > > accumulate_delta(data, channel, cpu, reg); > > *val = div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_units)); > > > and drop amd_add_delta(). > > Regards, > Naveenk > > -----Original Message----- > From: Guenter Roeck <linux@xxxxxxxxxxxx> > Sent: Sunday, November 22, 2020 7:00 PM > To: Chatradhi, Naveen Krishna <NaveenKrishna.Chatradhi@xxxxxxx> > Cc: Salvatore Bonaccorso <carnil@xxxxxxxxxx>; linux-hwmon@xxxxxxxxxxxxxxx; naveenkrishna.ch@xxxxxxxxx; stable@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] hwmon: amd_energy: modify the visibility of the counters > > [CAUTION: External Email] > > On Sun, Nov 22, 2020 at 06:56:24AM +0000, Chatradhi, Naveen Krishna wrote: > > [AMD Official Use Only - Approved for External Use] > > > > Hi Guenter, Salvatore > > > > > This is very unusual, and may mess up the "sensors" command. > > > What problem is this trying to solve ? > > Guenter, sorry for the delayed response. > > This fix is required to address the possible side channel attack reported in CVE-2020-12912. > > > [ ... ] > > > > >> ? > > Yes, Salvatore, thanks for bringing the links. > > > A much better fix would have been to cache RAPL data for a short period of time. To avoid any possibility of attacks, maybe add some random interval. Something like this: > > In accumulate_delta(): > accums->next_update = jiffies + HZ / 2 + get_random_int % HZ; > > In amd_energy_read(): > accum = &data->accums[channel]; > if (time_after(accum->next_update)) > accumulate_delta(data, channel, cpu, reg); > *val = div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_units)); > > and drop amd_add_delta(). > > Guenter
