From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97A59C43460 for ; Wed, 31 Mar 2021 13:50:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CA63600D3 for ; Wed, 31 Mar 2021 13:50:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235793AbhCaNtk (ORCPT ); Wed, 31 Mar 2021 09:49:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235630AbhCaNtM (ORCPT ); Wed, 31 Mar 2021 09:49:12 -0400 Received: from mail-ot1-x32c.google.com (mail-ot1-x32c.google.com [IPv6:2607:f8b0:4864:20::32c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90A57C061574; Wed, 31 Mar 2021 06:49:11 -0700 (PDT) Received: by mail-ot1-x32c.google.com with SMTP id v24-20020a9d69d80000b02901b9aec33371so18971003oto.2; Wed, 31 Mar 2021 06:49:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=90V6/8WcZ7wZDuZMIocWQ9L7DdYjn1t/LqSZtSrrOEE=; b=G49tIdwjULMU2Cqeu4wjE9DJpNFdYzUzXvbGYDhfrshdU49qL96tuafW4r8WWOiXjy IiABPvUy/fpQ5dkLiVs0IpHOr877FNBPI1r53vVzV8Jut/ZEXtbaoBcq01axwXVOYjMN Y9Qhfn7nFPF9EfrrbFoIZDRXl91tBhgz+o6w2DYYd7krZO9Sv4fbKPfkKTmfLONgLiCb XNo2VK3fdv2sCk9IMVBHdhiZB5MdC7ffdF2ThZEsEf4kvRlKHZUGXmqJFRTVicC3I8SS AGu67yQjpKh3wJdc5SU27SshiS8c1BI2Gd/EdNLtqJUZreTDG9VQvEvbr5ho4F+wyh0Q PCRA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id :mime-version:content-transfer-encoding; bh=90V6/8WcZ7wZDuZMIocWQ9L7DdYjn1t/LqSZtSrrOEE=; b=AEMoQbADkyPfgDpJZ3wSeDuFRBcfNHq3+Ig1+nAP+yg5fmVpRXKokIVbEFT67ZWm4E A32/YtQ5Rwsq++S93rpuIuqyGmobsGoPsjGEO6zeFvMc6ZN4QoqL1NdoSS5v3oxuJSLI 9bPJ0wxftfAdYV8mBzclPEWDORFC+L2V/LnI5DvixUKBP8KNpVXINeQPda3UCwDYF3+w EsYkAKQUzzgSZhMCHCEg7Qht6m9oja+DGJKu0ZlzG8qrjMlrwOqglBpNFORvjoD/dCLs 5JpjrBUDl4+mS2fYVK5UBMxRJ8HjCtaNgWo51BAkJzDm2pvg9rIdRkBdm4tdWJ3v9puH U2Kg== X-Gm-Message-State: AOAM532+6Fxjruq7YuYqPl+HzGL/GWrLvm1xgviRhQOsNVGuDFTZZNuN 2+qaPG+VwJh1y+qFFfirh2ocDz4wPYY= X-Google-Smtp-Source: ABdhPJyKZQ/7mfET1BKou4Gs8LrRSiG03Y5/DSZiL29qpaKeu49K/eOB9OGMET8jwk6Qnk8uNZ99+g== X-Received: by 2002:a9d:5e94:: with SMTP id f20mr2720526otl.150.1617198550279; Wed, 31 Mar 2021 06:49:10 -0700 (PDT) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id l81sm448719oif.31.2021.03.31.06.49.09 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 31 Mar 2021 06:49:09 -0700 (PDT) Sender: Guenter Roeck From: Guenter Roeck To: Hardware Monitoring Cc: linux-kernel@vger.kernel.org, Jean Delvare , Guenter Roeck , Naveen Krishna Chatradhi , Greg Kroah-Hartman Subject: [PATCH] hwmon: (amd_energy) Restore visibility of energy counters Date: Wed, 31 Mar 2021 06:49:02 -0700 Message-Id: <20210331134902.94720-1-linux@roeck-us.net> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 60268b0e8258 ("hwmon: (amd_energy) modify the visibility of the counters") restricted visibility of AMD energy counters to work around a side-channel attack. The attack is described in 'PLATYPUS: Software-based Power Side-Channel Attacks on x86'. It relies on quick and accurate power readings. Limiting power readings to privileged users is annoying. A much better solution is to make power 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 Fixes: 60268b0e8258 ("hwmon: (amd_energy) modify the visibility of the counters") Signed-off-by: Guenter Roeck --- drivers/hwmon/amd_energy.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/drivers/hwmon/amd_energy.c b/drivers/hwmon/amd_energy.c index a86cc8d6d93d..2ee6919eea57 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 +36,8 @@ struct sensor_accumulator { u64 energy_ctr; u64 prev_value; + u64 cached_value; + unsigned long cache_timeout; }; struct amd_energy_data { @@ -93,6 +96,8 @@ static void accumulate_delta(struct amd_energy_data *data, accum->prev_value + input; accum->prev_value = input; + accum->cached_value = input; + accum->cache_timeout = jiffies + HZ + get_random_int() % HZ; mutex_unlock(&data->lock); } @@ -125,16 +130,21 @@ static void amd_add_delta(struct amd_energy_data *data, int ch, u64 input; mutex_lock(&data->lock); - rdmsrl_safe_on_cpu(cpu, reg, &input); - input &= AMD_ENERGY_MASK; accum = &data->accums[ch]; - if (input >= accum->prev_value) - input += accum->energy_ctr - - accum->prev_value; - else - input += UINT_MAX - accum->prev_value + - accum->energy_ctr; + if (!accum->cached_value || time_after(jiffies, accum->cache_timeout)) { + rdmsrl_safe_on_cpu(cpu, reg, &input); + input &= AMD_ENERGY_MASK; + + if (input >= accum->prev_value) + input += accum->energy_ctr - accum->prev_value; + else + input += UINT_MAX - accum->prev_value + accum->energy_ctr; + accum->cached_value = input; + accum->cache_timeout = jiffies + HZ + get_random_int() % HZ; + } else { + input = accum->cached_value; + } /* Energy consumed = (1/(2^ESU) * RAW * 1000000UL) μJoules */ *val = div64_ul(input * 1000000UL, BIT(data->energy_units)); @@ -171,7 +181,7 @@ 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) -- 2.17.1