This is a note to let you know that I've just added the patch titled perf/x86: Fix uninitialized value usage to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: perf-x86-fix-uninitialized-value-usage.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e01d8718de4170373cd7fbf5cf6f9cb61cebb1e9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Wed, 27 Jan 2016 23:24:29 +0100 Subject: perf/x86: Fix uninitialized value usage From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> commit e01d8718de4170373cd7fbf5cf6f9cb61cebb1e9 upstream. When calling intel_alt_er() with .idx != EXTRA_REG_RSP_* we will not initialize alt_idx and then use this uninitialized value to index an array. When that is not fatal, it can result in an infinite loop in its caller __intel_shared_reg_get_constraints(), with IRQs disabled. Alternative error modes are random memory corruption due to the cpuc->shared_regs->regs[] array overrun, which manifest in either get_constraints or put_constraints doing weird stuff. Only took 6 hours of painful debugging to find this. Neither GCC nor Smatch warnings flagged this bug. Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> Cc: David Ahern <dsahern@xxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: Kan Liang <kan.liang@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Namhyung Kim <namhyung@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Stephane Eranian <eranian@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vince Weaver <vincent.weaver@xxxxxxxxx> Fixes: ae3f011fc251 ("perf/x86/intel: Fix SLM MSR_OFFCORE_RSP1 valid_mask") Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/cpu/perf_event_intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/cpu/perf_event_intel.c +++ b/arch/x86/kernel/cpu/perf_event_intel.c @@ -1937,7 +1937,8 @@ intel_bts_constraints(struct perf_event static int intel_alt_er(int idx, u64 config) { - int alt_idx; + int alt_idx = idx; + if (!(x86_pmu.flags & PMU_FL_HAS_RSP_1)) return idx; Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are queue-4.4/perf-x86-fix-uninitialized-value-usage.patch