Re: [PATCH v2 4/4] arm64: kaslr: support randomized module area with KASAN_VMALLOC

[Lecopzer Chen]

> 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@xxxxxxxxxx>
> > Signed-off-by: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
> > ---
> >  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.

thanks,
Lecopzer