From e01d8718de4170373cd7fbf5cf6f9cb61cebb1e9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 27 Jan 2016 23:24:29 +0100 Subject: [PATCH] perf/x86: Fix uninitialized value usage 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) Cc: Arnaldo Carvalho de Melo Cc: David Ahern Cc: Jiri Olsa Cc: Kan Liang Cc: Linus Torvalds Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Fixes: ae3f011fc251 ("perf/x86/intel: Fix SLM MSR_OFFCORE_RSP1 valid_mask") Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c index a667078a5180..4264a084e59b 100644 --- a/arch/x86/kernel/cpu/perf_event_intel.c +++ b/arch/x86/kernel/cpu/perf_event_intel.c @@ -1960,7 +1960,8 @@ intel_bts_constraints(struct perf_event *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;