Hi,
> -drive
> if=pflash,format=raw,unit=0,file=/root/kernels/qemu-install/OVMF_CODE.fd,readonly=on
> -drive if=pflash,format=raw,unit=1,file=./fedora.fd
> In this case, only OVMF_CODE.fd will be encrypted.
> The fedora.fd (OVMF_VARS.fd) will be unencrypted.
> -drive
> if=pflash,format=raw,unit=0,file=/root/kernels/qemu-install/OVMF.fd,readonly=on
> In this case, OVMF.fd will be encrypted, which includes the now memory
> backed variable store.
> > Can AmdSevInitialize() setup the mappings?
>
> Is there a way to tell when OVMF.fd vs OVMF_VARS.fd/OVMF_CODE.fd is used?
Hmm, good question. Can the guest figure what memory ranges are part
of the launch measurement?
I have a patch here (attached below) which refines flash detection and
can detect whenever varstore flash is writable or not. I suspect that
doesn't help much though as flash probing requires mappings already
being correct.
take care,
Gerd
commit fdab276a9f8a25f505b083b5e15180d093f515e3
Author: Gerd Hoffmann <kra...@redhat.com>
Date: Tue Apr 4 11:25:37 2023 +0200
OvmfPkg/QemuFlashFvbServicesRuntimeDxe: refine flash detection
diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
index 82b2b70441bf..c088d560f829 100644
--- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
+++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c
@@ -118,8 +118,17 @@ QemuFlashDetected (
*Ptr = OriginalUint8;
} else if (ProbeUint8 == CLEARED_ARRAY_STATUS) {
DEBUG ((DEBUG_INFO, "QemuFlashDetected => FD behaves as FLASH\n"));
- FlashDetected = TRUE;
- *Ptr = READ_ARRAY_CMD;
+ *Ptr = WRITE_BYTE_CMD;
+ *Ptr = OriginalUint8;
+ *Ptr = READ_STATUS_CMD;
+ ProbeUint8 = *Ptr;
+ if (ProbeUint8 & 0x10 /* programming error */) {
+ DEBUG ((DEBUG_INFO, "QemuFlashDetected => FLASH is readonly\n"));
+ } else {
+ DEBUG ((DEBUG_INFO, "QemuFlashDetected => FLASH is writable\n"));
+ FlashDetected = TRUE;
+ }
+ *Ptr = READ_ARRAY_CMD;
}
}
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