linux-kernel - Re: [PATCH 1/2] riscv: Fix asan-stack clang build

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Date:   Wed, 27 Oct 2021 16:06:24 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     alexandre.ghiti@...onical.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        ryabinin.a.a@...il.com, glider@...gle.com, andreyknvl@...il.com,
        dvyukov@...gle.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        alexandre.ghiti@...onical.com, nathan@...nel.org
Subject:     Re: [PATCH 1/2] riscv: Fix asan-stack clang build

On Tue, 26 Oct 2021 21:58:42 PDT (-0700), alexandre.ghiti@...onical.com wrote:
> Nathan reported that because KASAN_SHADOW_OFFSET was not defined in
> Kconfig, it prevents asan-stack from getting disabled with clang even
> when CONFIG_KASAN_STACK is disabled: fix this by defining the
> corresponding config.
>
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Alexandre Ghiti <alexandre.ghiti@...onical.com>
> ---
>  arch/riscv/Kconfig             | 6 ++++++
>  arch/riscv/include/asm/kasan.h | 3 +--
>  arch/riscv/mm/kasan_init.c     | 3 +++
>  3 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c1abbc876e5b..79250b1ed54e 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -162,6 +162,12 @@ config PAGE_OFFSET
>  	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
>  	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
>
> +config KASAN_SHADOW_OFFSET
> +	hex
> +	depends on KASAN_GENERIC
> +	default 0xdfffffc800000000 if 64BIT
> +	default 0xffffffff if 32BIT

I thought I posted this somewhere, but this is exactly what my first 
guess was.  The problem is that it's hanging on boot for me.  I don't 
really have anything exotic going on, it's just a defconfig with 
CONFIG_KASAN=y running in QEMU.

Does this boot for you?

> +
>  config ARCH_FLATMEM_ENABLE
>  	def_bool !NUMA
>
> diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
> index a2b3d9cdbc86..b00f503ec124 100644
> --- a/arch/riscv/include/asm/kasan.h
> +++ b/arch/riscv/include/asm/kasan.h
> @@ -30,8 +30,7 @@
>  #define KASAN_SHADOW_SIZE	(UL(1) << ((CONFIG_VA_BITS - 1) - KASAN_SHADOW_SCALE_SHIFT))
>  #define KASAN_SHADOW_START	KERN_VIRT_START
>  #define KASAN_SHADOW_END	(KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
> -#define KASAN_SHADOW_OFFSET	(KASAN_SHADOW_END - (1ULL << \
> -					(64 - KASAN_SHADOW_SCALE_SHIFT)))
> +#define KASAN_SHADOW_OFFSET	_AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>
>  void kasan_init(void);
>  asmlinkage void kasan_early_init(void);
> diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> index d7189c8714a9..8175e98b9073 100644
> --- a/arch/riscv/mm/kasan_init.c
> +++ b/arch/riscv/mm/kasan_init.c
> @@ -17,6 +17,9 @@ asmlinkage void __init kasan_early_init(void)
>  	uintptr_t i;
>  	pgd_t *pgd = early_pg_dir + pgd_index(KASAN_SHADOW_START);
>
> +	BUILD_BUG_ON(KASAN_SHADOW_OFFSET !=
> +		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
> +
>  	for (i = 0; i < PTRS_PER_PTE; ++i)
>  		set_pte(kasan_early_shadow_pte + i,
>  			mk_pte(virt_to_page(kasan_early_shadow_page),