Messages in this thread Patch in this message | | | Date | Mon, 15 Jun 2020 16:53:36 +0200 | From | Marco Elver <> | Subject | Re: [PATCH -tip v3 1/2] kcov: Make runtime functions noinstr-compatible |
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On Mon, 15 Jun 2020, Peter Zijlstra wrote:
> On Mon, Jun 15, 2020 at 09:53:06AM +0200, Marco Elver wrote: > > > > Disabling KCOV for smp_processor_id now moves the crash elsewhere. In > > the case of KASAN into its 'memcpy' wrapper, called after > > __this_cpu_read in fixup_bad_iret. This is making me suspicious, > > because it shouldn't be called from the noinstr functions. > > With your .config, objtool complains about exactly that though: > > vmlinux.o: warning: objtool: fixup_bad_iret()+0x8e: call to memcpy() leaves .noinstr.text section > > The utterly gruesome thing below 'cures' that.
Is __memcpy() generally available? I think that bypasses KASAN and whatever else.
> > For KCSAN the crash still happens in check_preemption_disabled, in the > > inlined native_save_fl function (apparently on its 'pushf'). If I turn > > fixup_bad_iret's __this_cpu_read into a raw_cpu_read (to bypass > > check_preemption_disabled), no more crash with KCSAN. > > vmlinux.o: warning: objtool: debug_smp_processor_id()+0x0: call to __sanitizer_cov_trace_pc() leaves .noinstr.text section > vmlinux.o: warning: objtool: check_preemption_disabled()+0x1f: call to __sanitizer_cov_trace_pc() leaves .noinstr.text section > vmlinux.o: warning: objtool: __this_cpu_preempt_check()+0x4: call to __sanitizer_cov_trace_pc() leaves .noinstr.text section > > That could be either of those I suppose, did you have the NOP patches > on? Let me try... those seem to placate objtool at least. > > I do see a fair amount of __kasan_check*() crud though: > > vmlinux.o: warning: objtool: rcu_nmi_exit()+0x44: call to __kasan_check_read() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x1c: call to __kasan_check_write() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_nmi_enter()+0x46: call to __kasan_check_read() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x21: call to __kasan_check_write() leaves .noinstr.text section > vmlinux.o: warning: objtool: __rcu_is_watching()+0x1c: call to __kasan_check_read() leaves .noinstr.text section > vmlinux.o: warning: objtool: debug_locks_off()+0x1b: call to __kasan_check_write() leaves .noinstr.text section > > That wasn't supported to happen with the __no_sanitize patches on (which > I didn't forget). Aah, I think we've lost a bunch of patches.. /me goes > rummage. > > This: > > https://lkml.kernel.org/r/20200603114051.896465666@infradead.org > > that cures the rcu part of that. > > Let me go look at your KCSAN thing now...
I tried to find the stack that is used by the crashing code -- which led me to entry_stack? So I tried this:
--- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -370,7 +370,7 @@ struct x86_hw_tss { #define IO_BITMAP_OFFSET_INVALID (__KERNEL_TSS_LIMIT + 1) struct entry_stack { - unsigned long words[64]; + unsigned long words[128]; }; struct entry_stack_page { No more crash. But that's probably not what we want. Just a datapoint.
> --- > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index af75109485c26..031a21fb5a741 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -675,6 +675,14 @@ struct bad_iret_stack { > struct pt_regs regs; > }; > > +void __always_inline __badcpy(void *dst, void *src, int nr) > +{ > + unsigned long *d = dst, *s = src; > + nr /= sizeof(unsigned long); > + while (nr--) > + *(d++) = *(s++); > +} > +
If we can use __memcpy() here, that would probably solve that.
Thanks, -- Marco
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