Re: [PATCH] x86: fix q35 kernel measurements broken due to rng seeding

[Jason A. Donenfeld]

This is already fixed via the patch that MST just sent in his pull. So wait a few days for that to be merged and it'll be all set.

No need for this patch here. Do not merge.

On Wed, Feb 1, 2023, 08:57 James Bottomley <jejb@linux.ibm.com> wrote:

The origin commit for rng seeding 67f7e426e5 ("hw/i386: pass RNG seed
via setup_data entry") modifies the kernel image file to append a
random seed.  Obviously this makes the hash of the kernel file
non-deterministic and so breaks both measured and some signed boots.
The commit notes it's only for non-EFI (because EFI has a different
RNG seeding mechanism) so, since there are no non-EFI q35 systems, this
should be disabled for the whole of the q35 machine type to bring back
deterministic kernel file hashes.

Obviously this still leaves the legacy bios case broken for at least
measured boot, but I don't think anyone cares about that now.

Signed-off-by: James Bottomley <jejb@linux.ibm.com>
---
 hw/i386/pc_q35.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 83c57c6eb1..11e8dd7ca7 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -357,6 +357,7 @@ static void pc_q35_machine_options(MachineClass *m)
     pcmc->default_nic_model = "e1000e";
     pcmc->pci_root_uid = 0;
     pcmc->default_cpu_version = 1;
+    pcmc->legacy_no_rng_seed = true;

     m->family = "pc_q35";
     m->desc = "Standard PC (Q35 + ICH9, 2009)";
@@ -394,9 +395,7 @@ DEFINE_Q35_MACHINE(v7_2, "pc-q35-7.2", NULL,

 static void pc_q35_7_1_machine_options(MachineClass *m)
 {
-    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
     pc_q35_7_2_machine_options(m);
-    pcmc->legacy_no_rng_seed = true;
     compat_props_add(m->compat_props, hw_compat_7_1,
hw_compat_7_1_len);
     compat_props_add(m->compat_props, pc_compat_7_1,
pc_compat_7_1_len);
 }
--
2.35.3