fw_meta: check that firmware memory regions do not overlap with kernel

Check that the memory regions provided by the SEV firmware metadata do
not overlap with kernel memory before validating them. Not doing this
could lead to the SVSM doubly validating its own memory, which allows
for remapping attacks.

Fixes: #114
Signed-off-by: Carlos López <[email protected]>

src/fw_meta.rs

@@ -9,6 +9,7 @@ extern crate alloc;
 use crate::address::PhysAddr;
 use crate::cpu::percpu::this_cpu_mut;
 use crate::error::SvsmError;
+use crate::kernel_launch::KernelLaunchInfo;
 use crate::mm::PerCPUPageMappingGuard;
 use crate::mm::SIZE_1G;
 use crate::sev::ghcb::PageStateChangeOp;
@@ -414,7 +415,10 @@ fn validate_fw_memory_vec(regions: Vec<MemoryRegion<PhysAddr>>) -> Result<(), Sv
     validate_fw_memory_vec(next_vec)
 }
 
-pub fn validate_fw_memory(fw_meta: &SevFWMetaData) -> Result<(), SvsmError> {
+pub fn validate_fw_memory(
+    fw_meta: &SevFWMetaData,
+    launch_info: &KernelLaunchInfo,
+) -> Result<(), SvsmError> {
     // Initalize vector with regions from the FW
     let mut regions = fw_meta.valid_mem.clone();
 
@@ -436,6 +440,13 @@ pub fn validate_fw_memory(fw_meta: &SevFWMetaData) -> Result<(), SvsmError> {
     // Sort regions by base address
     regions.sort_unstable_by_key(|a| a.start());
 
+    let kernel_region = launch_info.kernel_region();
+    for region in regions.iter() {
+        if region.overlap(&kernel_region) {
+            panic!("FwMeta region ovelaps with kernel");
+        }
+    }
+
     validate_fw_memory_vec(regions)
 }
 

src/svsm.rs

@@ -442,7 +442,7 @@ pub extern "C" fn svsm_main() {
 
     print_fw_meta(&fw_meta);
 
-    if let Err(e) = validate_fw_memory(&fw_meta) {
+    if let Err(e) = validate_fw_memory(&fw_meta, &LAUNCH_INFO) {
         panic!("Failed to validate firmware memory: {:#?}", e);
     }