[PATCH v3 1/8] arm/arm64: KVM: Formalise end of direct linear map

[Steve Capper]

On Thu, May 10, 2018 at 06:11:35PM +0100, Marc Zyngier wrote:
> [+Christoffer]
>
> Hi Steve,

Hi Marc,

>
> On 10/05/18 17:23, Steve Capper wrote:
> > We assume that the direct linear map ends at ~0 in the KVM HYP map
> > intersection checking code. This assumption will become invalid later on
> > for arm64 when the address space of the kernel is re-arranged.
> >
> > This patch introduces a new constant PAGE_OFFSET_END for both arm and
> > arm64 and defines it to be ~0UL
> >
> > Signed-off-by: Steve Capper <steve.capper at arm.com>
> > ---
> >  arch/arm/include/asm/memory.h   | 1 +
> >  arch/arm64/include/asm/memory.h | 1 +
> >  virt/kvm/arm/mmu.c              | 4 ++--
> >  3 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> > index ed8fd0d19a3e..45c211fd50da 100644
> > --- a/arch/arm/include/asm/memory.h
> > +++ b/arch/arm/include/asm/memory.h
> > @@ -24,6 +24,7 @@
> >
> >  /* PAGE_OFFSET - the virtual address of the start of the kernel image */
> >  #define PAGE_OFFSET                UL(CONFIG_PAGE_OFFSET)
> > +#define PAGE_OFFSET_END            (~0UL)
> >
> >  #ifdef CONFIG_MMU
> >
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > index 49d99214f43c..c5617cbbf1ff 100644
> > --- a/arch/arm64/include/asm/memory.h
> > +++ b/arch/arm64/include/asm/memory.h
> > @@ -61,6 +61,7 @@
> >     (UL(1) << VA_BITS) + 1)
> >  #define PAGE_OFFSET                (UL(0xffffffffffffffff) - \
> >     (UL(1) << (VA_BITS - 1)) + 1)
> > +#define PAGE_OFFSET_END            (~0UL)
> >  #define KIMAGE_VADDR               (MODULES_END)
> >  #define MODULES_END                (MODULES_VADDR + MODULES_VSIZE)
> >  #define MODULES_VADDR              (VA_START + KASAN_SHADOW_SIZE)
> > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> > index 7f6a944db23d..22af347d65f1 100644
> > --- a/virt/kvm/arm/mmu.c
> > +++ b/virt/kvm/arm/mmu.c
> > @@ -1927,10 +1927,10 @@ int kvm_mmu_init(void)
> >     kvm_debug("IDMAP page: %lx\n", hyp_idmap_start);
> >     kvm_debug("HYP VA range: %lx:%lx\n",
> >               kern_hyp_va(PAGE_OFFSET),
> > -             kern_hyp_va((unsigned long)high_memory - 1));
> > +             kern_hyp_va(PAGE_OFFSET_END));
> >
> >     if (hyp_idmap_start >= kern_hyp_va(PAGE_OFFSET) &&
> > -       hyp_idmap_start <  kern_hyp_va((unsigned long)high_memory - 1) &&
> > +       hyp_idmap_start <  kern_hyp_va(PAGE_OFFSET_END) &&
>
> This doesn't feel right to me now that we have the HYP randomization
> code merged. The way kern_hyp_va works now is only valid for addresses
> between VA(memblock_start_of_DRAM()) and high_memory.
>
> I fear that you could trigger the failing condition below as you
> evaluate the idmap address against something that is now not a HYP VA.
>
> >         hyp_idmap_start != (unsigned long)__hyp_idmap_text_start) {
> >             /*
> >              * The idmap page is intersecting with the VA space,
> >

Thanks! Yes, this patch is completely spurious, apologies I think I
made a mistake rebasing my V2 series on top of HASLR (originally I replaced
~0LL with PAGE_OFFSET_END in V1). I will drop this patch from the next version
of the series.

>
> I'd appreciate if you could keep me cc'd on this series.

Apologies, I'll be much more careful with git send-email.

Cheers,
--
Steve
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