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Re: [PATCH v3 0/2] x86/sev: Measured Linux SEV guest with kernel/initrd/

From: Connor Kuehl
Subject: Re: [PATCH v3 0/2] x86/sev: Measured Linux SEV guest with kernel/initrd/cmdline
Date: Thu, 8 Jul 2021 09:41:24 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

Hi Paolo,

Please consider this series[1] for inclusion into your next pull request.

Just a note that this series has a companion series that is getting
upstreamed into OVMF[2]

[1] Patchwork link, if convenient: 
[2] https://bugzilla.tianocore.org/show_bug.cgi?id=3457#c6

Thank you,


On 6/24/21 3:20 AM, Dov Murik wrote:
> Currently booting with -kernel/-initrd/-append is not supported in SEV
> confidential guests, because the content of these blobs is not measured
> and therefore not trusted by the SEV guest.
> However, in some cases the kernel, initrd, and cmdline are not secret
> but should not be modified by the host.  In such a case, we want to
> verify inside the trusted VM that the kernel, initrd, and cmdline are
> indeed the ones expected by the Guest Owner, and only if that is the
> case go on and boot them up (removing the need for grub inside OVMF in
> that mode).
> To support that, OVMF adds a special area for hashes of
> kernel/initrd/cmdline; that area is expected to be filled by QEMU and
> encrypted as part of the initial SEV guest launch.  This in turn makes
> the hashes part of the PSP measured content, and OVMF can trust these
> inputs if they match the hashes.
> This series adds an SEV function to generate the table of hashes for
> OVMF and encrypt it (patch 1/2), and calls this function if SEV is
> enabled when the kernel/initrd/cmdline are prepared (patch 2/2).
> Corresponding OVMF support was submitted to edk2-devel [1] (patch series
> "Measured SEV boot with kernel/initrd/cmdline"); it's still under
> review.
> [1] https://edk2.groups.io/g/devel/topic/patch_v1_0_8_measured_sev/83074450
> ---
> v3 changes:
>  - initrd hash is now mandatory; if no -initrd is passed, calculate the
>    hash of the empty buffer.  This is now aligned with the OVMF
>    behaviour which verifies the empty initrd (correctly).
>  - make SevHashTable entries fixed: 3 entries for cmdline, initrd, and kernel.
>  - in sev_add_kernel_loader_hashes: first calculate all the hashes, only then
>    fill-in the hashes table in the guest's memory.
>  - Use g_assert_not_reached in sev-stub.c.
>  - Use QEMU_PACKED attribute for structs.
>  - Use QemuUUID type for guids.
>  - in sev_add_kernel_loader_hashes: use ARRAY_SIZE(iov) instead of literal 2.
> v2: 
> https://lore.kernel.org/qemu-devel/20210621190553.1763020-1-dovmurik@linux.ibm.com/
> v2 changes:
>  - Extract main functionality to sev.c (with empty stub in sev-stub.c)
>  - Use sev_enabled() instead of machine->cgs->ready to detect SEV guest
>  - Coding style changes
> v1: 
> https://lore.kernel.org/qemu-devel/20210525065931.1628554-1-dovmurik@linux.ibm.com/
> Dov Murik (2):
>   sev/i386: Introduce sev_add_kernel_loader_hashes for measured linux
>     boot
>   x86/sev: generate SEV kernel loader hashes in x86_load_linux
>  target/i386/sev_i386.h |  12 ++++
>  hw/i386/x86.c          |  25 +++++++-
>  target/i386/sev-stub.c |   5 ++
>  target/i386/sev.c      | 137 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 178 insertions(+), 1 deletion(-)
> base-commit: b22726abdfa54592d6ad88f65b0297c0e8b363e2

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