Hi Alex,
On 2020-06-05 13:16, Alexandru Elisei wrote:
Hi Marc,
On 6/5/20 11:49 AM, Marc Zyngier wrote:
Recent changes made to Linux 5.8 have outlined that kvmtool
hardcodes the text offset instead of reading it from the arm64
image itself.
To address this, import the image header structure into kvmtool
and do the right thing. 32bit guests are still loaded to their
usual locations.
Reported-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
Makefile | 1 +
arm/aarch32/include/kvm/kvm-arch.h | 2 +-
arm/aarch64/include/asm/image.h | 59
++++++++++++++++++++++++++++++
arm/aarch64/include/kvm/kvm-arch.h | 5 +--
arm/aarch64/kvm.c | 30 +++++++++++++++
arm/kvm.c | 2 +-
6 files changed, 94 insertions(+), 5 deletions(-)
create mode 100644 arm/aarch64/include/asm/image.h
create mode 100644 arm/aarch64/kvm.c
[..]
This is a great addition to kvmtool, thank you! Before I do a more
in-depth
review, I have some general questions.
Regarding the actual value of text_offset, the booting.rst document
says:
"Prior to v3.17, the endianness of text_offset was not specified. In
these cases
image_size is zero and text_offset is 0x80000 in the endianness of the
kernel.
Where image_size is non-zero image_size is little-endian and must be
respected.
Where image_size is zero, text_offset can be assumed to be 0x80000".
All header fields are declared little-endian, which looks to me like it
would
break kernels older than 3.17. If that was intentional, I think it's
worth
documenting somewhere, or at least a comment for the
kvm__arch_get_kern_offset
function.
TBH, I didn't give pre-3.17 *big-endian* much thought. Happy to document
it though.
Now that we are parsing the kernel header, have you considered
checking the magic
number to make sure the user specified a valid kernel image? It might
save someone
some time debugging why the kernel isn't booting, if, for example, they
are
booting an armv7 kernel, but they forgot to specify --aarch32.
That'd be interesting. I'd be reluctant to prevent it from booting
altogether, but I can definitely detect the lack of signature and
print a warning.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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