Enable BTI and expose it in the EFI memory attributes table

3 files changed, 55 insertions, 4 deletions

diff --git a/.cargo/config b/.cargo/config
index 7747509..61914ed 100644
--- a/.cargo/config
+++ b/.cargo/config
@@ -1,6 +1,6 @@
 [target.aarch64-unknown-linux-gnu]
 rustflags = ["-C", "relocation-model=static", "-C", "link-arg=-Wl,-Tsrc/efilite.lds,--orphan-handling=error", "-C", "link-arg=-nostartfiles",
-	"-C", "target-feature=+crc,+rand"]
+	"-C", "target-feature=+crc,+rand","-Z", "branch-protection=bti"]
 
 [build]
 target = "aarch64-unknown-linux-gnu"
diff --git a/Cargo.toml b/Cargo.toml
index a91a356..0411c5f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,4 +20,4 @@ panic = "abort"
 
 [profile.release]
 panic = "abort"
-lto = true
+#lto = true   # breaks BTI
diff --git a/src/efi/mod.rs b/src/efi/mod.rs
index 158ab91..00aea0a 100644
--- a/src/efi/mod.rs
+++ b/src/efi/mod.rs
@@ -3,10 +3,11 @@
 // Author: Ard Biesheuvel <ardb@google.com>
 
 use crate::efi::{systemtable::*, loadedimage::*, memorytype::*};
-use crate::efi::MemoryType::{EfiBootServicesCode, EfiBootServicesData};
+use crate::efi::MemoryType::*;
 use crate::efi::loadedimage::EFI_LOADED_IMAGE_PROTOCOL_GUID;
 use crate::efi::configtable::ConfigurationTable;
-use crate::DTB;
+use crate::efi::memmap::*;
+use crate::{DTB, RTSCODE, RTSDATA};
 
 use crate::pecoff::Parser;
 
@@ -81,6 +82,10 @@ pub const EFI_RT_PROPERTIES_TABLE_GUID: Guid = guid!(
     0xeb66918a, 0x7eef, 0x402a, [0x84, 0x2e, 0x93, 0x1d, 0x21, 0xc3, 0x8a, 0xe9]
 );
 
+pub const EFI_MEMORY_ATTRIBUTES_TABLE_GUID: Guid = guid!(
+    0xdcfa911d, 0x26eb, 0x469f, [0xa2, 0x20, 0x38, 0xb7, 0xdc, 0x46, 0x12, 0x20]
+);
+
 const EFI_RT_SUPPORTED_GET_TIME: u32                   = 0x0001;
 const EFI_RT_SUPPORTED_GET_VARIABLE: u32               = 0x0010;
 const EFI_RT_SUPPORTED_GET_NEXT_VARIABLE_NAME: u32     = 0x0020;
@@ -103,6 +108,50 @@ static RT_PROPERTIES_TABLE: RtPropertiesTable = RtPropertiesTable {
         EFI_RT_SUPPORTED_RESET_SYSTEM,
 };
 
+const EFI_MEMORY_ATTRIBUTES_FLAGS_RT_FORWARD_CONTROL_FLOW_GUARD: u32 = 0x1;
+
+#[repr(C)]
+struct MemoryAttributesTable {
+    version: u32,
+    number_of_entries: u32,
+    descriptor_size: u32,
+    flags: u32,
+    entry: [MemoryDescriptor; 2]
+}
+
+impl MemoryAttributesTable {
+    pub fn new() -> &'static MemoryAttributesTable {
+        let m = alloc::boxed::Box::new(MemoryAttributesTable {
+            version: 2,
+            number_of_entries: 2,
+            descriptor_size: core::mem::size_of::<MemoryDescriptor>() as u32,
+            flags:
+                EFI_MEMORY_ATTRIBUTES_FLAGS_RT_FORWARD_CONTROL_FLOW_GUARD,
+            entry: [
+                MemoryDescriptor {
+                    r#type: EfiRuntimeServicesCode,
+                    physical_start: unsafe { RTSCODE.as_ptr() } as u64,
+                    virtual_start: 0x0,
+                    number_of_pages: unsafe {
+                        core::mem::size_of_val(&RTSCODE) as u64 >> EFI_PAGE_SHIFT
+                    },
+                    attribute: EFI_MEMORY_RO,
+                },
+                MemoryDescriptor {
+                    r#type: EfiRuntimeServicesData,
+                    physical_start: unsafe { RTSDATA.as_ptr() } as u64,
+                    virtual_start: 0x0,
+                    number_of_pages: unsafe {
+                        core::mem::size_of_val(&RTSDATA) as u64 >> EFI_PAGE_SHIFT
+                    },
+                    attribute: EFI_MEMORY_XP,
+                }
+            ],
+        });
+        alloc::boxed::Box::leak(m)
+    }
+}
+
 pub(crate) use guid;
 
 type ProtocolDb = BTreeMap::<(Handle, Guid), *const ()>;
@@ -123,6 +172,8 @@ pub fn init() {
                         &RT_PROPERTIES_TABLE as *const _ as *const ());
     install_configtable(&DTB_GUID,
                         unsafe { DTB.as_ptr() } as *const ());
+    install_configtable(&EFI_MEMORY_ATTRIBUTES_TABLE_GUID,
+                        MemoryAttributesTable::new() as *const _ as *const ());
 }
 
 pub fn install_protocol<T>(