x86, trace: Fix CR2 corruption when tracing page faults
The trace_do_page_fault function trigger tracepoint
and then handles the actual page fault.
This could lead to error if the tracepoint caused page
fault. The original cr2 value gets lost and the original
page fault handler kills current process with SIGSEGV.
This happens if you record page faults with callchain
data, the user part of it will cause tracepoint handler
to page fault:
# perf record -g -e exceptions:page_fault_user ls
Fixing this by saving the original cr2 value
and using it after tracepoint handler is done.
v2: Moving the cr2 read before exception_enter, because
it could trigger tracepoint as well.
Reported-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1402211701380.6395@vincent-weaver-1.um.maine.edu
Link: http://lkml.kernel.org/r/20140228160526.GD1133@krava.brq.redhat.com
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 6dea040..e7fa28b 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1022,11 +1022,11 @@
* routines.
*/
static void __kprobes
-__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)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
- unsigned long address;
struct mm_struct *mm;
int fault;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
@@ -1034,9 +1034,6 @@
tsk = current;
mm = tsk->mm;
- /* Get the faulting address: */
- address = read_cr2();
-
/*
* Detect and handle instructions that would cause a page fault for
* both a tracked kernel page and a userspace page.
@@ -1252,9 +1249,11 @@
do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
enum ctx_state prev_state;
+ /* Get the faulting address: */
+ unsigned long address = read_cr2();
prev_state = exception_enter();
- __do_page_fault(regs, error_code);
+ __do_page_fault(regs, error_code, address);
exception_exit(prev_state);
}
@@ -1271,9 +1270,16 @@
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
+ * reading) and destroy the original cr2 value, so read
+ * the faulting address now.
+ */
+ unsigned long address = read_cr2();
prev_state = exception_enter();
trace_page_fault_entries(regs, error_code);
- __do_page_fault(regs, error_code);
+ __do_page_fault(regs, error_code, address);
exception_exit(prev_state);
}