[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;
> In amd_energy_read():
> accum = &data->accums[channel];
> if (time_after(accum->next_update))
Do you mean if (time_after(jiffies, 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().
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
