On 4/13/19 1:31 AM, Laszlo Ersek wrote:
> RH covscan justifiedly reports a path through InstallXenTables() where
> DsdtTable can technically remain NULL.
>
> If this occurs in practice, then the guest and the VMM are out of sync on
> the interface contract. Catch the situation with a code snippet that halts
> in RELEASE builds, and in DEBUG builds lets the platform DSC control the
> assert disposition first (i.e. CPU exception, deadloop, or nothing).
>
>> Error: CLANG_WARNING:
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:309:14: warning: Access
>> to field 'Length' results in a dereference of a null pointer (loaded
>> from variable 'DsdtTable')
>> # DsdtTable->Length,
>> # ^~~~~~~~~
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:154:3: note: Null
>> pointer value stored to 'DsdtTable'
>> # DsdtTable = NULL;
>> # ^~~~~~~~~~~~~~~~~~
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:162:3: note: Taking
>> false branch
>> # if (EFI_ERROR (Status)) {
>> # ^
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:170:7: note: Assuming
>> the condition is false
>> # if (XenAcpiRsdpStructurePtr->XsdtAddress) {
>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:170:3: note: Taking
>> false branch
>> # if (XenAcpiRsdpStructurePtr->XsdtAddress) {
>> # ^
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:220:12: note: Assuming
>> the condition is false
>> # else if (XenAcpiRsdpStructurePtr->RsdtAddress) {
>> # ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:220:8: note: Taking
>> false branch
>> # else if (XenAcpiRsdpStructurePtr->RsdtAddress) {
>> # ^
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:274:3: note: Taking
>> false branch
>> # if (Fadt2Table) {
>> # ^
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:288:8: note: Taking
>> false branch
>> # else if (Fadt1Table) {
>> # ^
>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:309:14: note: Access to
>> field 'Length' results in a dereference of a null pointer (loaded from
>> variable 'DsdtTable')
>> # DsdtTable->Length,
>> # ^~~~~~~~~
>> # 307| AcpiProtocol,
>> # 308| DsdtTable,
>> # 309|-> DsdtTable->Length,
>> # 310| &TableHandle
>> # 311| );
>
> Cc: Anthony Perard <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
> Cc: Jordan Justen <[email protected]>
> Cc: Julien Grall <[email protected]>
> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
> Issue: scan-0993.txt
> Signed-off-by: Laszlo Ersek <[email protected]>
> ---
> OvmfPkg/AcpiPlatformDxe/Xen.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/OvmfPkg/AcpiPlatformDxe/Xen.c b/OvmfPkg/AcpiPlatformDxe/Xen.c
> index c8f275a8ee84..b21d3db74dc8 100644
> --- a/OvmfPkg/AcpiPlatformDxe/Xen.c
> +++ b/OvmfPkg/AcpiPlatformDxe/Xen.c
> @@ -295,18 +295,25 @@ InstallXenTables (
> &TableHandle
> );
> if (EFI_ERROR (Status)) {
> return Status;
> }
> }
>
> //
> - // Install DSDT table.
> + // Install DSDT table. If we reached this point without finding the DSDT,
> + // then we're out of sync with the hypervisor, and cannot continue.
> //
> + if (DsdtTable == NULL) {
> + DEBUG ((DEBUG_ERROR, "%a: no DSDT found\n", __FUNCTION__));
> + ASSERT (FALSE);
> + CpuDeadLoop ();
> + }
> +
> Status = InstallAcpiTable (
> AcpiProtocol,
> DsdtTable,
> DsdtTable->Length,
> &TableHandle
> );
> if (EFI_ERROR (Status)) {
> return Status;
>
Reviewed-by: Philippe Mathieu-Daude <[email protected]>
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