linux-kernel - Re: [PATCH v2 4/9] KVM: arm64: Add guard pages for pKVM (protected nVHE) hypervisor stack

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Date:   Tue, 22 Feb 2022 12:30:11 -0800
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Fuad Tabba <tabba@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Joey Gouly <joey.gouly@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 4/9] KVM: arm64: Add guard pages for pKVM (protected
 nVHE) hypervisor stack

On Tue, Feb 22, 2022 at 10:55 AM Mark Rutland <mark.rutland@....com> wrote:
>
> On Tue, Feb 22, 2022 at 08:51:05AM -0800, Kalesh Singh wrote:
> > Maps the stack pages in the flexible private VA range and allocates
> > guard pages below the stack as unbacked VA space. The stack is aligned
> > to twice its size to aid overflow detection (implemented in a subsequent
> > patch in the series).
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/setup.c | 25 +++++++++++++++++++++----
> >  1 file changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> > index 27af337f9fea..69df21320b09 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> > @@ -105,11 +105,28 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
> >               if (ret)
> >                       return ret;
> >
> > -             end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va;
> > +             /*
> > +              * Private mappings are allocated upwards from __io_map_base
> > +              * so allocate the guard page first then the stack.
> > +              */
> > +             start = (void *)pkvm_alloc_private_va_range(PAGE_SIZE, PAGE_SIZE);
> > +             if (IS_ERR_OR_NULL(start))
> > +                     return PTR_ERR(start);
>
> As on a prior patch, this usage of PTR_ERR() pattern is wrong when the
> ptr is NULL.

Ack. I'll fix these in the next version.

Thanks,
Kalesh
>
> > +             /*
> > +              * The stack is aligned to twice its size to facilitate overflow
> > +              * detection.
> > +              */
> > +             end = (void *)per_cpu_ptr(&kvm_init_params, i)->stack_pa;
> >               start = end - PAGE_SIZE;
> > -             ret = pkvm_create_mappings(start, end, PAGE_HYP);
> > -             if (ret)
> > -                     return ret;
> > +             start = (void *)__pkvm_create_private_mapping((phys_addr_t)start,
> > +                                     PAGE_SIZE, PAGE_SIZE * 2, PAGE_HYP);
> > +             if (IS_ERR_OR_NULL(start))
> > +                     return PTR_ERR(start);
>
> Likewise.
>
> Thanks,
> Mark.
>
> > +             end = start + PAGE_SIZE;
> > +
> > +             /* Update stack_hyp_va to end of the stack's private VA range */
> > +             per_cpu_ptr(&kvm_init_params, i)->stack_hyp_va = (unsigned long) end;
> >       }
> >
> >       /*
> > --
> > 2.35.1.473.g83b2b277ed-goog
> >