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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Daniel Axtens <dja@axtens.net>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kasan-dev@googlegroups.com, linux-mm@kvack.org
Subject: Re: [PATCH v5 3/3] powerpc/32: Add KASAN support
In-Reply-To: <3429fe33b68206ecc2a725a740937bbaef2d1ac8.1549935251.git.christophe.leroy@c-s.fr>
References: <cover.1549935247.git.christophe.leroy@c-s.fr> <3429fe33b68206ecc2a725a740937bbaef2d1ac8.1549935251.git.christophe.leroy@c-s.fr>
Date:   Mon, 18 Feb 2019 20:27:47 +1100
Message-ID: <87a7itqwdo.fsf@concordia.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Christophe Leroy <christophe.leroy@c-s.fr> writes:

> diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
> index e0637730a8e7..dba2c1038363 100644
> --- a/arch/powerpc/include/asm/ppc_asm.h
> +++ b/arch/powerpc/include/asm/ppc_asm.h
> @@ -251,6 +251,10 @@ GLUE(.,name):
>  
>  #define _GLOBAL_TOC(name) _GLOBAL(name)
>  
> +#define KASAN_OVERRIDE(x, y) \
> +	.weak x;	     \
> +	.set x, y
> +

Can you add a comment describing what that does and why?

> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 879b36602748..fc4c42262694 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -16,8 +16,9 @@ CFLAGS_prom_init.o      += -fPIC
>  CFLAGS_btext.o		+= -fPIC
>  endif
>  
> -CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> -CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> +CFLAGS_early_32.o += -DDISABLE_BRANCH_PROFILING
> +CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) -DDISABLE_BRANCH_PROFILING
> +CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) -DDISABLE_BRANCH_PROFILING

Why do we need to disable branch profiling now?

I'd probably be happier if all the CFLAGS changes were done in a leadup
patch to make them more obvious.

> diff --git a/arch/powerpc/kernel/prom_init_check.sh b/arch/powerpc/kernel/prom_init_check.sh
> index 667df97d2595..da6bb16e0876 100644
> --- a/arch/powerpc/kernel/prom_init_check.sh
> +++ b/arch/powerpc/kernel/prom_init_check.sh
> @@ -16,8 +16,16 @@
>  # If you really need to reference something from prom_init.o add
>  # it to the list below:
>  
> +grep CONFIG_KASAN=y .config >/dev/null

Just to be safe "^CONFIG_KASAN=y$" ?

> +if [ $? -eq 0 ]
> +then
> +	MEMFCT="__memcpy __memset"
> +else
> +	MEMFCT="memcpy memset"
> +fi

MEM_FUNCS ?

> diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> index 3bf9fc6fd36c..ce8d4a9f810a 100644
> --- a/arch/powerpc/lib/Makefile
> +++ b/arch/powerpc/lib/Makefile
> @@ -8,6 +8,14 @@ ccflags-$(CONFIG_PPC64)	:= $(NO_MINIMAL_TOC)
>  CFLAGS_REMOVE_code-patching.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_feature-fixups.o = $(CC_FLAGS_FTRACE)
>  
> +KASAN_SANITIZE_code-patching.o := n
> +KASAN_SANITIZE_feature-fixups.o := n
> +
> +ifdef CONFIG_KASAN
> +CFLAGS_code-patching.o += -DDISABLE_BRANCH_PROFILING
> +CFLAGS_feature-fixups.o += -DDISABLE_BRANCH_PROFILING
> +endif

There's that branch profiling again, though here it's only if KASAN is enabled.

> diff --git a/arch/powerpc/mm/kasan_init.c b/arch/powerpc/mm/kasan_init.c
> new file mode 100644
> index 000000000000..bd8e0a263e12
> --- /dev/null
> +++ b/arch/powerpc/mm/kasan_init.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#define DISABLE_BRANCH_PROFILING
> +
> +#include <linux/kasan.h>
> +#include <linux/printk.h>
> +#include <linux/memblock.h>
> +#include <linux/sched/task.h>
> +#include <asm/pgalloc.h>
> +
> +void __init kasan_early_init(void)
> +{
> +	unsigned long addr = KASAN_SHADOW_START;
> +	unsigned long end = KASAN_SHADOW_END;
> +	unsigned long next;
> +	pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(addr), addr), addr);

Can none of those fail?


cheers