linux-kernel - Re: [PATCH -mm] ubsan, x86: disable alignemnt checks for arch/x86/*

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Date:	Tue, 2 Feb 2016 00:09:00 +0300
From:	Mike Krinkin <krinkin.m.u@...il.com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	akpm@...ux-foundation.org, ying.huang@...ux.intel.com,
	davej@...emonkey.org.uk, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] ubsan, x86: disable alignemnt checks for arch/x86/*

Works well for me, thank you.

Tested-by: Mike Krinkin <krinkin.m.u@...il.com>

On Mon, Feb 01, 2016 at 08:08:19PM +0300, Andrey Ryabinin wrote:
> On 01/30/2016 03:36 AM, Mike Krinkin wrote:
> > option CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled,
> > i. e kernel with CONFIG_UBSAN_ALIGNMENT fails to load without even any
> > error message.
> >
> > The problem is that ubsan callbacks use spinlocks and might be called
> > before lockdep is initialized.
> 
> There is also report from kernel test robot:
> [    0.000000] WARNING: lockdep init error: lock 'report_lock' was acquired before lockdep_init().
> [    0.000000] Call stack leading to lockdep invocation was:
> [    0.000000]  [<b9e30ec5>] save_stack_trace+0x26/0x16d
> [    0.000000]  [<b9f98054>] __lock_acquire+0x237/0x15a4
> [    0.000000]  [<b9f994db>] lock_acquire+0x11a/0x1a9
> [    0.000000]  [<bae228f9>] _raw_spin_lock_irqsave+0x39/0x49
> [    0.000000]  [<ba5df852>] ubsan_prologue+0x1e/0x51
> [    0.000000]  [<ba5dfb02>] __ubsan_handle_type_mismatch+0xbd/0x14a
> [    0.000000]  [<bbca63c3>] reserve_ebda_region+0x8b/0x1bb
> [    0.000000]  [<bbca632c>] i386_start_kernel+0xf6/0x102
> [    0.000000]  [<ffffffff>] 0xffffffff
> 
> Let's disable aligment checks for x86-specific code since those are not
> useful.
> Changes around CFLAGS_UBSAN in this patch needed to be sure that cflags
> from 'subdir-ccflags-' appears only after CFLAGS_UBSAN.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Reported-by: kernel test robot <ying.huang@...ux.intel.com>
> Reported-by: Mike Krinkin <krinkin.m.u@...il.com>
> ---
>  Makefile               | 2 +-
>  arch/x86/Kbuild        | 2 ++
>  scripts/Makefile.lib   | 4 ++--
>  scripts/Makefile.ubsan | 5 +++++
>  4 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 6c1a3c2..1da29a0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -411,7 +411,7 @@ export MAKE AWK GENKSYMS INSTALLKERNEL PERL PYTHON UTS_MACHINE
>  export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
>  
>  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
> -export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KASAN CFLAGS_UBSAN
> +export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV CFLAGS_KASAN
>  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
>  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
>  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
> index 1538562..f1348ce 100644
> --- a/arch/x86/Kbuild
> +++ b/arch/x86/Kbuild
> @@ -21,3 +21,5 @@ obj-y += platform/
>  obj-y += net/
>  
>  obj-$(CONFIG_KEXEC_FILE) += purgatory/
> +
> +subdir-ccflags-$(CONFIG_UBSAN_ALIGNMENT) := $(call cc-option, -fno-sanitize=alignment)
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 2edbcad..d7342cf 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -132,8 +132,8 @@ endif
>  
>  ifeq ($(CONFIG_UBSAN),y)
>  _c_flags += $(if $(patsubst n%,, \
> -		$(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_SANITIZE)$(CONFIG_UBSAN_SANITIZE_ALL)), \
> -		$(CFLAGS_UBSAN))
> +		$(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_SANITIZE)$(CONFIG_UBSAN_SANITIZE_ALL)),, \
> +		$(DISABLE_UBSAN))
>  endif
>  
>  # If building the kernel in a separate objtree expand all occurrences
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 77ce538..91c1dd3 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -18,4 +18,9 @@ endif
>        # -fsanitize=* options makes GCC less smart than usual and
>        # increase number of 'maybe-uninitialized false-positives
>        CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)
> +
> +      KBUILD_CFLAGS += $(CFLAGS_UBSAN)
> +      export DISABLE_UBSAN
> +      DISABLE_UBSAN := $(call cc-option, -fno-sanitize=undefined)
> +      DISABLE_UBSAN += $(call cc-option, -Wmaybe-uninitialized)
>  endif
> -- 
> 2.4.10
>