Messages in this thread Patch in this message | | | Date | Thu, 21 Mar 2019 11:45:17 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry |
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On Thu, Mar 21, 2019 at 10:02:41AM +0100, Peter Zijlstra wrote: > On Thu, Mar 21, 2019 at 09:33:17AM +0100, Peter Zijlstra wrote: > > I'm thinking this problem wasn't new. > > > idtentry page_fault do_page_fault has_error_code=1 > > call error_entry > > TRACE_IRQS_OFF > > call trace_hardirqs_off* > > <tracer stuff> > > <fault> # modifies CR2 > > CALL_enter_from_user_mode > __context_tracking_exit() > trace_user_exit(0) > #PF > > > call do_page_fault > > address = read_cr2(); /* whoopsie */ > > And that also isn't fixed by your patch. > > I'm trying to make idtentry put cr2 in rdx, such that do_page_fault() > takes address as a 3rd argument, but I'm still fighting that context > tracking nonsense. >
Something a little like so; completely untested and obviously needs 32bit changes too.
--- arch/x86/entry/entry_64.S | 28 ++++++++++++++++------------ arch/x86/mm/fault.c | 3 +-- 2 files changed, 17 insertions(+), 14 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 1f0efdb7b629..776dbe7ba72e 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -879,7 +879,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt * @paranoid == 2 is special: the stub will never switch stacks. This is for * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS. */ -.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 +.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 read_cr2=0 ENTRY(\sym) UNWIND_HINT_IRET_REGS offset=\has_error_code*8 @@ -901,18 +901,28 @@ ENTRY(\sym) .if \paranoid call paranoid_entry + /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */ .else call error_entry + /* returned flag: ebx=1: CALL_enter_from_user_mode, ebx=0: don't need it */ .endif UNWIND_HINT_REGS - /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */ - .if \paranoid + .if \read_cr2 + mov %cr2, %rdx /* XXX paravirt crap */ + .endif + .if \shift_ist != -1 TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */ .else TRACE_IRQS_OFF .endif + + .if \paranoid == 0 + testl %ebx, %ebx + jz .Lno_context_tracking_\@ + CALL_enter_from_user_mode +.Lno_context_tracking_\@: .endif movq %rsp, %rdi /* pt_regs pointer */ @@ -1140,7 +1150,7 @@ idtentry xenint3 do_int3 has_error_code=0 #endif idtentry general_protection do_general_protection has_error_code=1 -idtentry page_fault do_page_fault has_error_code=1 +idtentry page_fault do_page_fault has_error_code=1 read_cr2=1 #ifdef CONFIG_KVM_GUEST idtentry async_page_fault do_async_page_fault has_error_code=1 @@ -1243,17 +1253,11 @@ ENTRY(error_entry) ENCODE_FRAME_POINTER pushq %r12 - /* - * We need to tell lockdep that IRQs are off. We can't do this until - * we fix gsbase, and we should do it before enter_from_user_mode - * (which can take locks). - */ - TRACE_IRQS_OFF - CALL_enter_from_user_mode + mov $1, %ebx /* CALL_enter_from_user_mode */ ret .Lerror_entry_done: - TRACE_IRQS_OFF + xorl %ebx, %ebx ret /* diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 667f1da36208..aac7a74869a2 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1560,9 +1560,8 @@ trace_page_fault_entries(unsigned long address, struct pt_regs *regs, * exception_{enter,exit}() contains all sorts of tracepoints. */ dotraplinkage void 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) { - unsigned long address = read_cr2(); /* Get the faulting address */ enum ctx_state prev_state; prev_state = exception_enter();
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