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

Lecopzer Chen
2021-01-28T08:54:54Z

> 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@kernel.org>
> > Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.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.

thanks,
Lecopzer