On Tue, 18 Dec 2018 at 14:00, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>
> On 12/12/2018 20:17, Dave Martin wrote:
> > Since commit d26c25a9d19b ("arm64: KVM: Tighten guest core register
> > access from userspace"), KVM_{GET,SET}_ONE_REG rejects register IDs
> > that do not correspond to a single underlying architectural register.
> >
> > KVM_GET_REG_LIST was not changed to match however: instead, it
> > simply yields a list of 32-bit register IDs that together cover the
> > whole kvm_regs struct. This means that if userspace tries to use
> > the resulting list of IDs directly to drive calls to KVM_*_ONE_REG,
> > some of those calls will now fail.
> >
> > This was not the intention. Instead, iterating KVM_*_ONE_REG over
> > the list of IDs returned by KVM_GET_REG_LIST should be guaranteed
> > to work.
> >
> > This patch fixes the problem by splitting validate_core_reg_id()
> > into a backend core_reg_size_from_offset() which does all of the
> > work except for checking that the size field in the register ID
> > matches, and kvm_arm_copy_reg_indices() and num_core_regs() are
> > converted to use this to enumerate the valid offsets.
> >
> > kvm_arm_copy_reg_indices() now also sets the register ID size field
> > appropriately based on the value returned, so the register ID
> > supplied to userspace is fully qualified for use with the register
> > access ioctls.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: d26c25a9d19b ("arm64: KVM: Tighten guest core register access from userspace")
> > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> > ---
> I'm quite keen on queuing this for 4.21, but I'd like Peter's seal of
> approval on it.
>
> Peter?
Sounds plausible, but I'm on holiday now til January, so if you
want a more detailed response than that (or even actual testing
with QEMU) it'll have to wait til next year. (Note that I never
tested d26c25a9d19b with QEMU either...)
thanks
-- PMM
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