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x86, trace: Further robustify CR2 handling vs tracing

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Building on commit 0ac09f9f8c ("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: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140306145300.GO9987@twins.programming.kicks-ass.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Peter Zijlstra
2014-03-05 14:07:49 +01:00
committed by H. Peter Anvin
parent 0ac09f9f8c
commit d4078e2322
1 changed files with 23 additions and 10 deletions
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33
arch/x86/mm/fault.c
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@@ -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, * This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate * and the problem, and then passes it off to one of the appropriate
* routines. * 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, __do_page_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address) unsigned long address)
{ {
@@ -1245,31 +1249,38 @@ good_area:
up_read(&mm->mmap_sem); up_read(&mm->mmap_sem);
} }
dotraplinkage void __kprobes dotraplinkage void __kprobes notrace
do_page_fault(struct pt_regs *regs, unsigned long error_code) 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; 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(); prev_state = exception_enter();
__do_page_fault(regs, error_code, address); __do_page_fault(regs, error_code, address);
exception_exit(prev_state); 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) unsigned long error_code)
{ {
if (user_mode(regs)) if (user_mode(regs))
trace_page_fault_user(read_cr2(), regs, error_code); trace_page_fault_user(address, regs, error_code);
else 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) trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
{ {
enum ctx_state prev_state;
/* /*
* The exception_enter and tracepoint processing could * The exception_enter and tracepoint processing could
* trigger another page faults (user space callchain * 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. * the faulting address now.
*/ */
unsigned long address = read_cr2(); unsigned long address = read_cr2();
enum ctx_state prev_state;
prev_state = exception_enter(); 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); __do_page_fault(regs, error_code, address);
exception_exit(prev_state); exception_exit(prev_state);
} }
#endif /* CONFIG_TRACING */