runtime: add mem_protect

src/runtime/link.x

@@ -17,19 +17,23 @@ MEMORY
 
 SECTIONS
 {
-    .text :
+    .text : ALIGN(0x1000000)
     {
+        __text_start = .;
         KEEP(*(.text.exceptions));
         *(.text.boot);
         *(.text .text.*);
+        __text_end = .;
     } > SDRAM
  
-    .rodata : ALIGN(4)
+    .rodata : ALIGN(0x1000000)
     {
+        __rodata_start = .;
         *(.rodata .rodata.*);
+        __rodata_end = .;
     } > SDRAM
  
-    .data : ALIGN(4)
+    .data : ALIGN(0x1000000)
     {
         *(.data .data.*);
     } > SDRAM

src/runtime/src/main.rs

@@ -11,6 +11,7 @@ use log::{info, error};
 use libboard_zynq::{timer::GlobalTimer, logger, devc};
 use libsupport_zynq::ram;
 
+mod mem_protect;
 mod sd_reader;
 mod config;
 mod proto_core_io;
@@ -44,6 +45,7 @@ pub fn main_core0() {
     log::set_max_level(log::LevelFilter::Debug);
     info!("NAR3/Zynq7000 starting...");
 
+    mem_protect::setup();
     ram::init_alloc_linker();
 
     match config::Config::new() {

src/runtime/src/mem_protect.rs

@@ -0,0 +1,39 @@
+use libcortex_a9::mmu::{AccessPermissions, L1_PAGE_SIZE, L1Table};
+
+/// Symbols defined by the linker script
+extern "C" {
+    static __text_start: usize;
+    static __text_end: usize;
+    static __rodata_start: usize;
+    static __rodata_end: usize;
+}
+
+/// Apply basic memory protection to the regions defined by the linker
+/// script for the runtime on core 0.
+///
+/// Therefore these regions need to be aligned to 1 MB.
+pub fn setup() {
+    let text_start = unsafe { &__text_start as *const _ as usize };
+    let text_end = unsafe { &__text_end as *const _ as usize };
+    let rodata_start = unsafe { &__rodata_start as *const _ as usize };
+    let rodata_end = unsafe { &__rodata_end as *const _ as usize };
+
+    let l1table = L1Table::get();
+    for addr in (0..0xFFFF_FFFF).step_by(L1_PAGE_SIZE) {
+        l1table.update(addr as *const usize, |l1section| {
+            if addr >= text_start && addr < text_end {
+                // Code: R-X
+                l1section.access = AccessPermissions::ReadOnly;
+                l1section.exec = true;
+            } else if addr >= rodata_start && addr < rodata_end {
+                // Data: R--
+                l1section.access = AccessPermissions::ReadOnly;
+                l1section.exec = false;
+            } else {
+                // Everything else: RW-
+                l1section.access = AccessPermissions::FullAccess;
+                l1section.exec = false;
+            }
+        });
+    }
+}