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

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Date:   Thu, 28 Jan 2021 20:26:49 +0000
From:   Will Deacon <will@...nel.org>
To:     Lecopzer Chen <lecopzer.chen@...iatek.com>
Cc:     akpm@...ux-foundation.org, andreyknvl@...gle.com, ardb@...nel.org,
        aryabinin@...tuozzo.com, broonie@...nel.org,
        catalin.marinas@....com, dan.j.williams@...el.com,
        dvyukov@...gle.com, glider@...gle.com, gustavoars@...nel.org,
        kasan-dev@...glegroups.com, lecopzer@...il.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-mm@...ck.org,
        linux@...ck-us.net, robin.murphy@....com, rppt@...nel.org,
        tyhicks@...ux.microsoft.com, vincenzo.frascino@....com,
        yj.chiang@...iatek.com
Subject: Re: [PATCH v2 4/4] arm64: kaslr: support randomized module area with
 KASAN_VMALLOC

On Thu, Jan 28, 2021 at 04:53:26PM +0800, Lecopzer Chen wrote:
>  
> > 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
> 
> CONFIG_KASAN_VMALLOC=y means CONFIG_KASAN_GENERIC=y
> but CONFIG_KASAN_GENERIC=y doesn't means CONFIG_KASAN_VMALLOC=y
> 
> So this if-condition allows only KASAN rather than
> KASAN + KASAN_VMALLOC enabled.
> 
> Please correct me if I'm wrong.

Sorry, you're completely right -- I missed the '!' when I read this
initially.

Will