From d4078e232267ff53f3b030b9698a3c001db4dbec Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 5 Mar 2014 14:07:49 +0100 Subject: [PATCH] x86, trace: Further robustify CR2 handling vs tracing Building on commit 0ac09f9f8cd1 ("x86, trace: Fix CR2 corruption when tracing page faults") this patch addresses another few issues: - Now that read_cr2() is lifted into trace_do_page_fault(), we should pass the address to trace_page_fault_entries() to avoid it re-reading a potentially changed cr2. - Put both trace_do_page_fault() and trace_page_fault_entries() under CONFIG_TRACING. - Mark both fault entry functions {,trace_}do_page_fault() as notrace to avoid getting __mcount or other function entry trace callbacks before we've observed CR2. - Mark __do_page_fault() as noinline to guarantee the function tracer does get to see the fault. Cc: Cc: Acked-by: Steven Rostedt Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140306145300.GO9987@twins.programming.kicks-ass.net Signed-off-by: H. Peter Anvin --- arch/x86/mm/fault.c | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e7fa28b..a10c8c7 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1020,8 +1020,12 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs) * This routine handles page faults. It determines the address, * and the problem, and then passes it off to one of the appropriate * routines. + * + * This function must have noinline because both callers + * {,trace_}do_page_fault() have notrace on. Having this an actual function + * guarantees there's a function trace entry. */ -static void __kprobes +static void __kprobes noinline __do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address) { @@ -1245,31 +1249,38 @@ good_area: up_read(&mm->mmap_sem); } -dotraplinkage void __kprobes +dotraplinkage void __kprobes notrace do_page_fault(struct pt_regs *regs, unsigned long error_code) { + unsigned long address = read_cr2(); /* Get the faulting address */ enum ctx_state prev_state; - /* Get the faulting address: */ - unsigned long address = read_cr2(); + + /* + * We must have this function tagged with __kprobes, notrace and call + * read_cr2() before calling anything else. To avoid calling any kind + * of tracing machinery before we've observed the CR2 value. + * + * exception_{enter,exit}() contain all sorts of tracepoints. + */ prev_state = exception_enter(); __do_page_fault(regs, error_code, address); exception_exit(prev_state); } -static void trace_page_fault_entries(struct pt_regs *regs, +#ifdef CONFIG_TRACING +static void trace_page_fault_entries(unsigned long address, struct pt_regs *regs, unsigned long error_code) { if (user_mode(regs)) - trace_page_fault_user(read_cr2(), regs, error_code); + trace_page_fault_user(address, regs, error_code); else - trace_page_fault_kernel(read_cr2(), regs, error_code); + trace_page_fault_kernel(address, regs, error_code); } -dotraplinkage void __kprobes +dotraplinkage void __kprobes notrace trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) { - enum ctx_state prev_state; /* * The exception_enter and tracepoint processing could * trigger another page faults (user space callchain @@ -1277,9 +1288,11 @@ trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) * the faulting address now. */ unsigned long address = read_cr2(); + enum ctx_state prev_state; prev_state = exception_enter(); - trace_page_fault_entries(regs, error_code); + trace_page_fault_entries(address, regs, error_code); __do_page_fault(regs, error_code, address); exception_exit(prev_state); } +#endif /* CONFIG_TRACING */ -- 2.7.4