On Fri, Feb 28, 2014 at 04:33:40PM +0100, Jiri Olsa wrote:
> 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.
>
> Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
> Cc: Paul Mackerras <pau...@samba.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Arnaldo Carvalho de Melo <a...@ghostprotocols.net>
> Cc: H. Peter Anvin <h...@zytor.com>
> Cc: Seiji Aguchi <seiji.agu...@hds.com>
> ---
> arch/x86/mm/fault.c | 25 ++++++++++++++++++-------
> 1 file changed, 18 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 9d591c8..52fad6c 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1016,11 +1016,11 @@ static inline bool smap_violation(int error_code,
> struct pt_regs *regs)
> * 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;
> @@ -1028,9 +1028,6 @@ __do_page_fault(struct pt_regs *regs, unsigned long
> error_code)
> 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.
> @@ -1248,9 +1245,14 @@ dotraplinkage void __kprobes
> do_page_fault(struct pt_regs *regs, unsigned long error_code)
> {
> enum ctx_state prev_state;
> + unsigned long address;
>
> prev_state = exception_enter();
> - __do_page_fault(regs, error_code);
> +
> + /* Get the faulting address: */
> + address = read_cr2();
> +
As Peter already stated, the address = read_cr2() needs to go before the
exception_enter() call.
> + __do_page_fault(regs, error_code, address);
> exception_exit(prev_state);
> }
>
> @@ -1267,9 +1269,18 @@ dotraplinkage void __kprobes
> trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
> {
> enum ctx_state prev_state;
> + unsigned long address;
>
> prev_state = exception_enter();
> +
> + /*
> + * The tracepoint processing could trigger another page
> + * fault (user space callchain reading) and destroy the
> + * original cr2 value, so read the faulting address now.
> + */
> + address = read_cr2();
Same here.
After that, you can add:
Acked-by: Steven Rostedt <rost...@goodmis.org>
-- Steve
> +
> trace_page_fault_entries(regs, error_code);
> - __do_page_fault(regs, error_code);
> + __do_page_fault(regs, error_code, address);
> exception_exit(prev_state);
> }
> --
> 1.7.11.7
>
> --
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