Commit d4078e23 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by H. Peter Anvin
Browse files

x86, trace: Further robustify CR2 handling vs tracing 



Building on commit 0ac09f9f ("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: <jolsa@redhat.com>
Cc: <vincent.weaver@maine.edu>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140306145300.GO9987@twins.programming.kicks-ass.net


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 0ac09f9f

arch/x86/mm/fault.c

+23 −10
Original line number Diff line number Diff line
@@ -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 */

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