linux-kernel - Re: [PATCH v2 4/4] arm64: kaslr: support randomized module area with KASAN

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Date:   Wed, 27 Jan 2021 23:04:14 +0000
From:   Will Deacon <will@...nel.org>
To:     Lecopzer Chen <lecopzer@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        dan.j.williams@...el.com, aryabinin@...tuozzo.com,
        glider@...gle.com, dvyukov@...gle.com, akpm@...ux-foundation.org,
        linux-mediatek@...ts.infradead.org, yj.chiang@...iatek.com,
        catalin.marinas@....com, ardb@...nel.org, andreyknvl@...gle.com,
        broonie@...nel.org, linux@...ck-us.net, rppt@...nel.org,
        tyhicks@...ux.microsoft.com, robin.murphy@....com,
        vincenzo.frascino@....com, gustavoars@...nel.org,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: Re: [PATCH v2 4/4] arm64: kaslr: support randomized module area with
 KASAN_VMALLOC

On Sat, Jan 09, 2021 at 06:32:52PM +0800, Lecopzer Chen wrote:
> After KASAN_VMALLOC works in arm64, we can randomize module region
> into vmalloc area now.
> 
> Test:
> 	VMALLOC area ffffffc010000000 fffffffdf0000000
> 
> 	before the patch:
> 		module_alloc_base/end ffffffc008b80000 ffffffc010000000
> 	after the patch:
> 		module_alloc_base/end ffffffdcf4bed000 ffffffc010000000
> 
> 	And the function that insmod some modules is fine.
> 
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> ---
>  arch/arm64/kernel/kaslr.c  | 18 ++++++++++--------
>  arch/arm64/kernel/module.c | 16 +++++++++-------
>  2 files changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
> index 1c74c45b9494..a2858058e724 100644
> --- a/arch/arm64/kernel/kaslr.c
> +++ b/arch/arm64/kernel/kaslr.c
> @@ -161,15 +161,17 @@ u64 __init kaslr_early_init(u64 dt_phys)
>  	/* use the top 16 bits to randomize the linear region */
>  	memstart_offset_seed = seed >> 48;
>  
> -	if (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
> -	    IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> +	if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) &&
> +	    (IS_ENABLED(CONFIG_KASAN_GENERIC) ||

CONFIG_KASAN_VMALLOC depends on CONFIG_KASAN_GENERIC so why is this
necessary?

Will