svsm: Allow the firmware metadata location to be specified via config

When using fw_cfg, the OVMF metadata is located at a hardcoded location
of 1 page below 4GB. When using IGVM for configuration it is possible
for the IGVM file to specify a different location for the firmware
itself so it makes sense to also specify a parameter to describe the
metdata page location. This commit adds a new IGVM parameter field and
uses this to determine the OVMF metadata location.

Signed-off-by: Roy Hopkins <roy.hopkins@suse.com>

igvm_params/src/lib.rs

@@ -56,6 +56,7 @@ pub struct IgvmParamBlock {
     pub debug_serial_port: u16,
 
     _reserved: u16,
+
     /// The guest physical address of the start of the guest firmware. The
     /// permissions on the pages in the firmware range are adjusted to the guest
     /// VMPL. If this field is zero then no firmware is launched after
@@ -66,6 +67,13 @@ pub struct IgvmParamBlock {
     /// no firmware is launched after initialization is complete.
     pub fw_size: u32,
 
+    /// The guest physical address of the page that contains metadata that
+    /// corresponds to the firmware. The SVSM expects the page to contain
+    /// metadata in the format defined by OVMF.
+    pub fw_metadata: u32,
+
+    _reserved2: u32,
+
     /// The amount of space that must be reserved at the base of the kernel
     /// memory region (e.g. for VMSA contents).
     pub kernel_reserved_size: u32,

src/config.rs

@@ -11,6 +11,7 @@ use crate::address::PhysAddr;
 use crate::error::SvsmError;
 use crate::fw_cfg::FwCfg;
 use crate::igvm_params::IgvmParams;
+use crate::mm::{PAGE_SIZE, SIZE_1G};
 use crate::serial::SERIAL_PORT;
 use crate::utils::MemoryRegion;
 use alloc::vec::Vec;
@@ -72,6 +73,16 @@ impl<'a> SvsmConfig<'a> {
         }
     }
 
+    pub fn get_fw_metadata(&self) -> Result<PhysAddr, SvsmError> {
+        match self {
+            SvsmConfig::FirmwareConfig(_) => {
+                // The metadata location always starts at 32 bytes below 4GB
+                Ok(PhysAddr::from((4 * SIZE_1G) - PAGE_SIZE))
+            }
+            SvsmConfig::IgvmConfig(igvm_params) => igvm_params.get_fw_metadata(),
+        }
+    }
+
     pub fn get_fw_regions(&self) -> Result<Vec<MemoryRegion<PhysAddr>>, SvsmError> {
         match self {
             SvsmConfig::FirmwareConfig(fw_cfg) => {

src/igvm_params.rs

@@ -140,6 +140,14 @@ impl IgvmParams<'_> {
         self.igvm_param_block.debug_serial_port
     }
 
+    pub fn get_fw_metadata(&self) -> Result<PhysAddr, SvsmError> {
+        if !self.should_launch_fw() || self.igvm_param_block.fw_metadata == 0 {
+            Err(Firmware)
+        } else {
+            Ok(PhysAddr::from(self.igvm_param_block.fw_metadata as u64))
+        }
+    }
+
     pub fn get_fw_regions(&self) -> Result<Vec<MemoryRegion<PhysAddr>>, SvsmError> {
         if !self.should_launch_fw() {
             Err(Firmware)

src/svsm.rs

@@ -38,7 +38,7 @@ use svsm::mm::alloc::{memory_info, print_memory_info, root_mem_init};
 use svsm::mm::memory::init_memory_map;
 use svsm::mm::pagetable::paging_init;
 use svsm::mm::virtualrange::virt_log_usage;
-use svsm::mm::{init_kernel_mapping_info, PerCPUPageMappingGuard, SIZE_1G};
+use svsm::mm::{init_kernel_mapping_info, PerCPUPageMappingGuard};
 use svsm::requests::{request_loop, update_mappings};
 use svsm::serial::SerialPort;
 use svsm::sev::secrets_page::{copy_secrets_page, disable_vmpck0, SecretsPage};
@@ -304,10 +304,9 @@ fn mapping_info_init(launch_info: &KernelLaunchInfo) {
     );
 }
 
-fn map_and_parse_fw_meta() -> Result<SevFWMetaData, SvsmError> {
-    // Map meta-data location, it starts at 32 bytes below 4GiB
-    let pstart = PhysAddr::from((4 * SIZE_1G) - PAGE_SIZE);
-    let guard = PerCPUPageMappingGuard::create_4k(pstart)?;
+fn map_and_parse_fw_meta(config: &SvsmConfig) -> Result<SevFWMetaData, SvsmError> {
+    // Map the metadata location which is defined by the firmware config
+    let guard = PerCPUPageMappingGuard::create_4k(config.get_fw_metadata()?)?;
     let vstart = guard.virt_addr().as_ptr::<u8>();
     // Safety: we just mapped a page, so the size must hold. The type
     // of the slice elements is `u8` so there are no alignment requirements.
@@ -460,7 +459,7 @@ pub extern "C" fn svsm_main() {
 
     let fw_metadata = if config.should_launch_fw() {
         Some(
-            map_and_parse_fw_meta()
+            map_and_parse_fw_meta(&config)
                 .unwrap_or_else(|e| panic!("Failed to parse FW SEV meta-data: {:#?}", e)),
         )
     } else {