Re: [PATCH 2/2] riscv: Add KASAN support

From: Christoph Hellwig <hch@infradead.org>
To: Nick Hu <nickhu@andestech.com>
Cc: aou@eecs.berkeley.edu, alankao@andestech.com,
	atish.patra@wdc.com, gregkh@linuxfoundation.org,
	palmer@sifive.com, linux-kernel@vger.kernel.org,
	kasan-dev@googlegroups.com, zong@andestech.com,
	alexios.zavras@intel.com, Anup.Patel@wdc.com, glider@google.com,
	green.hu@gmail.com, paul.walmsley@sifive.com,
	aryabinin@virtuozzo.com, tglx@linutronix.de, deanbo422@gmail.com,
	linux-riscv@lists.infradead.org, dvyukov@google.com
Subject: Re: [PATCH 2/2] riscv: Add KASAN support
Date: Mon, 12 Aug 2019 08:10:50 -0700	[thread overview]
Message-ID: <20190812151050.GJ26897@infradead.org> (raw)
In-Reply-To: <88358ef8f7cfcb7fd01b6b989eccaddbe00a1e57.1565161957.git.nickhu@andestech.com>

> 2. KASAN can't debug the modules since the modules are allocated in VMALLOC
> area. We mapped the shadow memory, which corresponding to VMALLOC area,
> to the kasan_early_shadow_page because we don't have enough physical space
> for all the shadow memory corresponding to VMALLOC area.

How do other architectures solve this problem?

> @@ -54,6 +54,8 @@ config RISCV
>  	select EDAC_SUPPORT
>  	select ARCH_HAS_GIGANTIC_PAGE
>  	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
> +	select GENERIC_STRNCPY_FROM_USER if KASAN

Is there any reason why we can't always enabled this?  Also just
enabling the generic efficient strncpy_from_user should probably be
a separate patch.

> +	select HAVE_ARCH_KASAN if MMU

Based on your cover letter this should be if MMU && 64BIT

>  #define __HAVE_ARCH_MEMCPY
>  extern asmlinkage void *memcpy(void *, const void *, size_t);
> +extern asmlinkage void *__memcpy(void *, const void *, size_t);
>  
>  #define __HAVE_ARCH_MEMMOVE
>  extern asmlinkage void *memmove(void *, const void *, size_t);
> +extern asmlinkage void *__memmove(void *, const void *, size_t);
> +
> +#define memcpy(dst, src, len) __memcpy(dst, src, len)
> +#define memmove(dst, src, len) __memmove(dst, src, len)
> +#define memset(s, c, n) __memset(s, c, n)

This looks weird and at least needs a very good comment.  Also
with this we effectively don't need the non-prefixed prototypes
anymore.  Also you probably want to split the renaming of the mem*
routines into a separate patch with a proper changelog.

>  #include <asm/tlbflush.h>
>  #include <asm/thread_info.h>
>  
> +#ifdef CONFIG_KASAN
> +#include <asm/kasan.h>
> +#endif

Any good reason to not just always include the header?

> +
>  #ifdef CONFIG_DUMMY_CONSOLE
>  struct screen_info screen_info = {
>  	.orig_video_lines	= 30,
> @@ -64,12 +68,17 @@ void __init setup_arch(char **cmdline_p)
>  
>  	setup_bootmem();
>  	paging_init();
> +
>  	unflatten_device_tree();

spurious whitespace change.

> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 23cd1a9..9700980 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -46,6 +46,7 @@ SECTIONS
>  		KPROBES_TEXT
>  		ENTRY_TEXT
>  		IRQENTRY_TEXT
> +		SOFTIRQENTRY_TEXT

Hmm.  What is the relation to kasan here?  Maybe we should add this
separately with a good changelog?

> +++ b/arch/riscv/mm/kasan_init.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0

This probably also wants a copyright statement.

> +	// init for swapper_pg_dir

Please use /* */ style comments.

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