linux-kernel - Re: [PATCH] um: Fix kcov crash before kernel is started.

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Message-ID: <3011782.xhPzxOy8Zy@blindfold>
Date:   Sat, 14 Oct 2017 10:05:41 +0200
From:   Richard Weinberger <richard@....at>
To:     Thomas Meyer <thomas@...3r.de>
Cc:     syzkaller@...glegroups.com,
        user-mode-linux-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] um: Fix kcov crash before kernel is started.

Am Samstag, 14. Oktober 2017, 00:00:25 CEST schrieb Thomas Meyer:
> UMLs current_thread_info() unconditionally assumes that the top of the stack
> contains the thread_info structure.
> Prevent kcov from using invalid curent_thread_info() data by disable
> instrumentation of early startup code.
> 
> Signed-off-by: Thomas Meyer <thomas@...3r.de>
> ---
>  arch/um/kernel/skas/Makefile | 2 ++
>  lib/Makefile                 | 4 ++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
> index 0b76d8869c94..df3aedb974a2 100644
> --- a/arch/um/kernel/skas/Makefile
> +++ b/arch/um/kernel/skas/Makefile
> @@ -3,6 +3,8 @@
>  # Licensed under the GPL
>  #
> 
> +KCOV_INSTRUMENT                := n

So, you disable kconv for the whole SKAS code?
That's a bit broad. ;-\

>  obj-y := clone.o mmu.o process.o syscall.o uaccess.o
> 
>  # clone.o is in the stub, so it can't be built with profiling
> diff --git a/lib/Makefile b/lib/Makefile
> index dafa79613fb4..18319ad5daab 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -16,6 +16,10 @@ KCOV_INSTRUMENT_list_debug.o := n
>  KCOV_INSTRUMENT_debugobjects.o := n
>  KCOV_INSTRUMENT_dynamic_debug.o := n
> 
> +ifdef CONFIG_UML
> +KCOV_INSTRUMENT_cmdline.o := n
> +endif
> +

huh? Why do we need an exception for UML here?

Thanks,
//richard