Re: [RFC kvmtool 18/31] arm64: Populate initial realm contents

[Suzuki K Poulose]

Hi Piotr

On 02/03/2023 14:03, Piotr Sawicki wrote:
> Hi,
>
> > From: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> >
> > Populate the realm memory with the initial contents, which include
> > the device tree blob, the kernel image, and initrd, if specified,
> > or the firmware image.
> >
> > Populating an image in the realm involves two steps:
> >   a) Mark the IPA area as RAM - INIT_IPA_REALM
> >   b) Load the contents into the IPA - POPULATE_REALM
> >
> > Wherever we know the actual size of an image in memory, we make
> > sure the "memory area" is initialised to RAM.
> > e.g., Linux kernel image size from the header which includes the bss etc.
> > The "file size" on disk for the Linux image is much smaller.
> > We mark the region of size Image.header.size as RAM (a), from the kernel
> > load address. And load the Image file into the memory (b) above.
> > At the moment we only detect the Arm64 Linux Image header format.
> >
> > Since we're already touching the code that copies the
> > initrd in guest memory, let's do a bit of cleaning and remove a
> > useless local variable.
> >
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> > [ Make sure the Linux kernel image area is marked as RAM ]
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>


> > diff --git a/arm/kvm.c b/arm/kvm.c
> > index acb627b2..57c5b5f7 100644
> > --- a/arm/kvm.c
> > +++ b/arm/kvm.c
> > @@ -6,6 +6,7 @@
> >   #include "kvm/fdt.h"
> >   #include "arm-common/gic.h"
> > +#include <asm/realm.h>
> >   #include <sys/resource.h>
> > @@ -167,6 +168,9 @@ bool kvm__arch_load_kernel_image(struct kvm *kvm, 
> > int fd_kernel, int fd_initrd,
> >       pr_debug("Loaded kernel to 0x%llx (%llu bytes)",
> >            kvm->arch.kern_guest_start, kvm->arch.kern_size);
>
>
> I've noticed that multiple calling of the measurement test from the 
> kvm-unit-tests suite results in different Realm Initial Measurements, 
> although the kernel image is always the same.
>
> After short investigation, I've found that the RIM starts being 
> different while populating the last 4kB chunk of the kernel image.
> The issue occurs when the image size is not aligned to the page size (4kB).
>
> After zeroing the unused area of the last chunk, the measurements become 
> repeatable.

That is a good point. We could memset() the remaining bits of the 4K 
page to 0. I will make this change.

Suzuki