On 19.09.24 17:00, Simon Glass wrote:
Hi,
On Thu, 19 Sept 2024 at 16:32, Ilias Apalodimas
<ilias.apalodi...@linaro.org> wrote:
Hi all,
On Thu, 19 Sept 2024 at 17:20, Heinrich Schuchardt
<heinrich.schucha...@canonical.com> wrote:
On 19.09.24 16:10, Simon Glass wrote:
Hi Heinrich,
On Sat, 14 Sept 2024 at 18:06, Heinrich Schuchardt
<heinrich.schucha...@canonical.com> wrote:
For measured be boot we must avoid any volatile values in the device-tree.
We already delete /chosen/kaslr-seed if we provide and EFI RNG protocol.
Could you explain a bit why this is, and where this is checked?
Additionally remove /chosen/rng-seed provided by QEMU or U-Boot.
Measured boot relies on creating hashes of artifacts and writing these
to TPM. If the hashes don't match the OS will either warn or refuse to
boot. The device-tree is one of the artifacts that are measured.
If we have random values in /chosen, measured boot will fail.
When an EFI RNG protocol is provided by the firmware, GRUB and the
kernel will use it instead of /chosen/rng-seed and /chosen/kaslr-seed.
There's a comment on top of that function that explains what happens as well.
In short the EFI stub does not even look at the KASLR seed and never
randomizes the physical placement of the kernel. It only does that
when the EFI_RNG protocol is there.
OK thank you. I suppose I am more just wondering why it got added in
the first place?
For booting via the legacy Linux entry point adding kaslr-seed allows to
randomize addresses. QEMU adds rng-seed instead of kaslr-seed.
Best regards
Heinrich
Regards,
Simon
Regards
/Ilias
Best regards
Heinrich
Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
---
include/efi_loader.h | 2 +-
lib/efi_loader/efi_dt_fixup.c | 15 ++++++++++-----
lib/efi_loader/efi_helper.c | 2 +-
3 files changed, 12 insertions(+), 7 deletions(-)
[..]
Regards,
Simon
