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[73.67.244.238]) by smtp.gmail.com with ESMTPSA id a21sm8804411pfe.81.2016.08.23.19.56.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 23 Aug 2016 19:56:43 -0700 (PDT) From: John Stultz To: lkml Cc: John Stultz , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , "Rafael J. Wysocki" , Janek Kozicki , Chen Yu , Xunlei Pang , Zhang Rui , linux-pm@vger.kernel.org, stable Subject: [RFC][PATCH v2] timekeeping: Cap array access in timekeeping_debug to protect against invalid sleep times Date: Tue, 23 Aug 2016 19:56:40 -0700 Message-Id: <1472007400-26563-1-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1471993702-29148-3-git-send-email-john.stultz@linaro.org> References: <1471993702-29148-3-git-send-email-john.stultz@linaro.org> It was reported that hibernation could fail on the 2nd attempt, where the system hangs at hibernate() -> syscore_resume() -> i8237A_resume() -> claim_dma_lock(), because the lock has already been taken. However there is actually no other process would like to grab this lock on that problematic platform. Further investigation showed that the problem is triggered by setting /sys/power/pm_trace to 1 before the 1st hibernation. Since once pm_trace is enabled, the RTC becomes unmeaningful after suspend, and meanwhile some BIOSes would like to adjust the 'invalid' RTC (e.g, smaller than 1970) to the release date of that motherboard during POST stage, thus after resumed, it may seem that the system had a significant long sleep time might due to meaningless RTC delta. Then in timekeeping_resume -> tk_debug_account_sleep_time, if the bit31 of the sleep time happened to be set to 1, the fls returns 32 and then we add 1 to sleep_time_bin[32], which caused a memory overwritten. As depicted by System.map: 0xffffffff81c9d080 b sleep_time_bin 0xffffffff81c9d100 B dma_spin_lock the dma_spin_lock.val is set to 1, which caused this problem. This patch adds a sanity check in tk_debug_account_sleep_time() to ensure we don't index past the sleep_time_bin array. Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Rafael J. Wysocki Cc: Janek Kozicki Cc: Chen Yu Cc: Xunlei Pang Cc: Zhang Rui Cc: linux-pm@vger.kernel.org Cc: stable Reported-by: Janek Kozicki Reported-by: Chen Yu [jstultz: Problem diagnosed and original patch by Chen Yu, I've solved the issue slightly differently, but borrowed his excelent explanation of of the issue here.] Signed-off-by: John Stultz --- v2: Minor tweaks to the commit message kernel/time/timekeeping_debug.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) -- 1.9.1 diff --git a/kernel/time/timekeeping_debug.c b/kernel/time/timekeeping_debug.c index f6bd652..107310a6 100644 --- a/kernel/time/timekeeping_debug.c +++ b/kernel/time/timekeeping_debug.c @@ -23,7 +23,9 @@ #include "timekeeping_internal.h" -static unsigned int sleep_time_bin[32] = {0}; +#define NUM_BINS 32 + +static unsigned int sleep_time_bin[NUM_BINS] = {0}; static int tk_debug_show_sleep_time(struct seq_file *s, void *data) { @@ -69,6 +71,9 @@ late_initcall(tk_debug_sleep_time_init); void tk_debug_account_sleep_time(struct timespec64 *t) { - sleep_time_bin[fls(t->tv_sec)]++; + /* Cap bin index so we don't overflow the array */ + int bin = min(fls(t->tv_sec), NUM_BINS-1); + + sleep_time_bin[bin]++; }