From 29044ad1509ecc229f1d5a31aeed7a8dc61a71c4 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 3 Mar 2010 02:25:22 +0100 Subject: [PATCH] x86/stacktrace: Don't dereference bad frame pointers Callers of a stacktrace might pass bad frame pointers. Those are usually checked for safety in stack walking helpers before any dereferencing, but this is not the case when we need to go through one more frame pointer that backlinks the irq stack to the previous one, as we don't have any reliable address boudaries to compare this frame pointer against. This raises crashes when we record callchains for ftrace events with perf because we don't use the right helpers to capture registers there. We get wrong frame pointers as we call task_pt_regs() even on kernel threads, which is a wrong thing as it gives us the initial state of any kernel threads freshly created. This is even not what we want for user tasks. What we want is a hot snapshot of registers when the ftrace event triggers, not the state before a task entered the kernel. This requires more thoughts to do it correctly though. So first put a guardian to ensure the given frame pointer can be dereferenced to avoid crashes. We'll think about how to fix the callers in a subsequent patch. Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Thomas Gleixner Cc: H. Peter Anvin Cc: Peter Zijlstra Cc: Paul Mackerras Cc: Steven Rostedt Cc: 2.6.33.x Cc: Arnaldo Carvalho de Melo --- arch/x86/kernel/dumpstack_64.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index 0ad9597073f5..a6c906c9b193 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -125,9 +125,15 @@ fixup_bp_irq_link(unsigned long bp, unsigned long *stack, { #ifdef CONFIG_FRAME_POINTER struct stack_frame *frame = (struct stack_frame *)bp; + unsigned long next; - if (!in_irq_stack(stack, irq_stack, irq_stack_end)) - return (unsigned long)frame->next_frame; + if (!in_irq_stack(stack, irq_stack, irq_stack_end)) { + if (!probe_kernel_address(&frame->next_frame, next)) + return next; + else + WARN_ONCE(1, "Perf: bad frame pointer = %p in " + "callchain\n", &frame->next_frame); + } #endif return bp; } -- 2.20.1