[edk2-devel] [PATCH v2] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Use physical address with SEV-ES
Lendacky, Thomas
thomas.lendacky at amd.com
Sat Jan 23 14:02:26 UTC 2021
On 1/23/21 7:57 AM, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky at amd.com>
>
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3183
>
> Under SEV-ES, a write to the flash device is done using a direct VMGEXIT
> to perform an MMIO write. The address provided to the MMIO write must be
> the physical address of the MMIO write destitnation. During boot, OVMF
> runs with an identity mapped pagetable structure so that VA == PA and the
> VMGEXIT MMIO write destination is just the virtual address of the flash
> area address being written.
>
> However, when the UEFI SetVitualAddressMap() API is invoked, an identity
> mapped pagetable structure may not be in place and using the virtual
> address for the flash area address is no longer valid. This results in
> writes to the flash not being performed successfully. This can be seen
> by attempting to change the boot order under Linux. The update will
> appear to be performed, based on the output of the command. But rebooting
> the guest will show that the new boot order has not been set.
>
> To remedy this, save the value of the flash base physical address before
> converting the address as part of SetVirtualAddressMap(). The physical
> address can then be calculated by obtaining the offset of the MMIO target
> virtual address relative to the flash base virtual address and adding that
> to the original flash base physical address. The resulting value produces
> a successful MMIO write during runtime services.
>
> Fixes: 437eb3f7a8db7681afe0e6064d3a8edb12abb766
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com> > ---
> .../QemuFlashDxe.c | 20 ++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
Forgot to add the changelog and use the diffstat options.
The changes address the comments from Laszlo on the v1 version of the patch:
- Update the last paragraph of the commit message
- Limit changes to only the QemuFlashDxe.c file
- Update expression for calculating the physical address
Thanks,
Tom
>
> diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c
> index 1b0742967f71..d303b0078b08 100644
> --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c
> +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c
> @@ -16,11 +16,17 @@
>
> #include "QemuFlash.h"
>
> +STATIC EFI_PHYSICAL_ADDRESS mSevEsFlashPhysBase;
> +
> VOID
> QemuFlashConvertPointers (
> VOID
> )
> {
> + if (MemEncryptSevEsIsEnabled ()) {
> + mSevEsFlashPhysBase = (UINTN) mFlashBase;
> + }
> +
> EfiConvertPointer (0x0, (VOID **) &mFlashBase);
> }
>
> @@ -52,11 +58,23 @@ QemuFlashPtrWrite (
> if (MemEncryptSevEsIsEnabled ()) {
> MSR_SEV_ES_GHCB_REGISTER Msr;
> GHCB *Ghcb;
> + EFI_PHYSICAL_ADDRESS PhysAddr;
> BOOLEAN InterruptState;
>
> Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
> Ghcb = Msr.Ghcb;
>
> + //
> + // The MMIO write needs to be to the physical address of the flash pointer.
> + // Since this service is available as part of the EFI runtime services,
> + // account for a non-identity mapped VA after SetVitualAddressMap().
> + //
> + if (mSevEsFlashPhysBase == 0) {
> + PhysAddr = (UINTN) Ptr;
> + } else {
> + PhysAddr = mSevEsFlashPhysBase + (Ptr - mFlashBase);
> + }
> +
> //
> // Writing to flash is emulated by the hypervisor through the use of write
> // protection. This won't work for an SEV-ES guest because the write won't
> @@ -68,7 +86,7 @@ QemuFlashPtrWrite (
> Ghcb->SharedBuffer[0] = Value;
> Ghcb->SaveArea.SwScratch = (UINT64) (UINTN) Ghcb->SharedBuffer;
> VmgSetOffsetValid (Ghcb, GhcbSwScratch);
> - VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, (UINT64) (UINTN) Ptr, 1);
> + VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, PhysAddr, 1);
> VmgDone (Ghcb, InterruptState);
> } else {
> *Ptr = Value;
>
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