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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q13sm17769121pjc.4.2019.11.30.08.33.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 30 Nov 2019 08:33:46 -0800 (PST) Date: Sat, 30 Nov 2019 08:33:44 -0800 From: Kees Cook To: Konstantin Khlebnikov Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Sasha Levin , Greg Kroah-Hartman , rcu@vger.kernel.org, Tejun Heo , Andrew Morton , Linus Torvalds , Thomas Gleixner Subject: Re: [PATCH 2/2] kernel: add sysctl kernel.nr_taints Message-ID: <201911300823.69EAF975E9@keescook> References: <157503370645.8187.6335564487789994134.stgit@buzz> <157503370887.8187.1663761929323284758.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <157503370887.8187.1663761929323284758.stgit@buzz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 29, 2019 at 04:21:48PM +0300, Konstantin Khlebnikov wrote: > Once taint flag is set it's never cleared. Following taint could be detected > only via parsing kernel log messages which are different for each occasion. > For repeatable taints like TAINT_MACHINE_CHECK, TAINT_BAD_PAGE, TAINT_DIE, > TAINT_WARN, TAINT_LOCKUP it would be good to know count to see their rate. > > This patch adds sysctl with vector of counters. One for each taint flag. > Counters are non-atomic in favor of simplicity. Exact count doesn't matter. > Writing vector of zeroes resets counters. > > This is useful for detecting frequent problems with automatic monitoring. > > Signed-off-by: Konstantin Khlebnikov I like this, yeah. This would let LKDTM users reset taint counts to re-check the same kernel, etc, without explicitly clearing the taint flags which always seemed like a bad idea. :) Reviewed-by: Kees Cook One nit below... > --- > include/linux/kernel.h | 1 + > kernel/panic.c | 2 ++ > kernel/sysctl.c | 9 +++++++++ > 3 files changed, 12 insertions(+) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index e8a6808e4f2f..900d02167bbd 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -604,6 +604,7 @@ struct taint_flag { > }; > > extern const struct taint_flag taint_flags[TAINT_FLAGS_COUNT]; > +extern int sysctl_nr_taints[TAINT_FLAGS_COUNT]; > > extern const char hex_asc[]; > #define hex_asc_lo(x) hex_asc[((x) & 0x0f)] > diff --git a/kernel/panic.c b/kernel/panic.c > index d7750a45ca8d..a3df00ebcba2 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -39,6 +39,7 @@ > int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE; > static unsigned long tainted_mask = > IS_ENABLED(CONFIG_GCC_PLUGIN_RANDSTRUCT) ? (1 << TAINT_RANDSTRUCT) : 0; > +int sysctl_nr_taints[TAINT_FLAGS_COUNT]; > static int pause_on_oops; > static int pause_on_oops_flag; > static DEFINE_SPINLOCK(pause_on_oops_lock); > @@ -434,6 +435,7 @@ void add_taint(unsigned flag, enum lockdep_ok lockdep_ok) > pr_warn("Disabling lock debugging due to kernel taint\n"); > > set_bit(flag, &tainted_mask); > + sysctl_nr_taints[flag]++; As long as we're changing this code, how about adding an explicit check of "flag" against either ARRAY_SIZE(sysctl_nr_tains) or TAINT_FLAGS_COUNT? It looks like only 1 caller isn't using a static value, though: proc_taint(), so it would catch "overflows" there (it's already bounded to the size of tainted_mask, but proc could set "unknown" taint flags). -Kees > } > EXPORT_SYMBOL(add_taint); > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index b6f2f35d0bcf..5d9727556cef 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -553,6 +553,15 @@ static struct ctl_table kern_table[] = { > .mode = 0644, > .proc_handler = proc_taint, > }, > + { > + .procname = "nr_taints", > + .data = &sysctl_nr_taints, > + .maxlen = sizeof(sysctl_nr_taints), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = SYSCTL_ZERO, > + .extra2 = SYSCTL_ZERO, > + }, > { > .procname = "sysctl_writes_strict", > .data = &sysctl_writes_strict, > -- Kees Cook