feat: Enhance MMU by separating sections and configuring permissions

README.md

@@ -14,8 +14,9 @@ NovaOS is a expository project where I build a kernel from scratch for a Raspber
 - Communicate with peripherals via mailboxes ✓
 - Frame Buffer ✓
 - Heap Memory allocation ✓
+- MMU
+- SVC instructions
 - Multi Core
 - Dynamic clock speed
-- MMU
 - Multiprocessing
 - Basic Terminal over UART

link.ld

@@ -27,34 +27,23 @@ SECTIONS {
         KEEP(*(.vector_table))
     }
 
-    .translation_table_l1 ALIGN(4096) : {
+    .heap ALIGN(16): {
-        __translation_table_l1_start = .;
-        . += 4096;
-        __translation_table_l1_end = .;
-    }
-
-    .translation_table_l2 ALIGN(4096) : {
-        __translation_table_l2_start = .;
-        . += 4096;
-        __translation_table_l2_end = .;
-    }
-
-    .heap : ALIGN(16)
-    {
     __heap_start = .;
     . += 100K; #100kB
     __heap_end = .;
     }
 
-    .stack : ALIGN(16)
+    .stack ALIGN(16): {
-    {
     __stack_start = .;
     . += 10K; #10kB stack
     __stack_end = .;
     }
 
-    .stack_el0 : ALIGN(2M)
+    . = ALIGN(2M);
-    {
+
+    __kernel_end = .;
+
+    .stack_el0 : {
     __stack_start_el0 = .;
     . += 10K; #10kB stack
     __stack_end_el0 = .;

src/aarch64/mmu.rs

@@ -1,60 +1,154 @@
-use core::ptr::write_volatile;
+use core::u64::MAX;
+
+use nova_error::NovaError;
 
 use crate::{println, PERIPHERAL_BASE};
 
 unsafe extern "C" {
-    static mut __translation_table_l1_start: u64;
     static mut __translation_table_l2_start: u64;
     static __stack_start_el0: u64;
+    static __kernel_end: u64;
     static _data: u64;
 }
 
-pub fn init_translation_table() {
-    unsafe {
-        write_volatile(
-            &raw mut __translation_table_l1_start,
-            table_descriptor_entry(&raw mut __translation_table_l2_start as u64),
-        );
-        println!("{}", &raw mut __translation_table_l2_start as u64);
-
-        for i in 0..512 {
-            let addr = 0x0 + (i as u64 * 2 * 1024 * 1024);
-
-            let descriptor = if addr < &_data as *const _ as u64 {
-                block_descriptor_entry(addr, NORMAL_MEM, USER_AP | DISALLOW_KERNEL_AP)
-            } else if addr < PERIPHERAL_BASE as u64 {
-                block_descriptor_entry(addr, NORMAL_MEM, KERNEL_AP)
-            } else {
-                block_descriptor_entry(addr, DEVICE_MEM, USER_AP)
-            };
-
-            write_volatile(
-                (&raw mut __translation_table_l2_start).byte_add(8 * i),
-                descriptor,
-            );
-        }
-    }
-}
-
 const BLOCK: u64 = 0b01;
 const TABLE: u64 = 0b11;
 
-const USER_AP: u64 = 1 << 6;
+const EL0_ACCESSIBLE: u64 = 1 << 6;
-const KERNEL_AP: u64 = 0 << 7;
+
-const DISALLOW_KERNEL_AP: u64 = 1 << 7;
+const WRITABLE: u64 = 0 << 7;
+const READ_ONLY: u64 = 1 << 7;
+
 const ACCESS_FLAG: u64 = 1 << 10;
 const INNER_SHAREABILITY: u64 = 0b11 << 8;
 
 const NORMAL_MEM: u64 = 0 << 2;
 const DEVICE_MEM: u64 = 1 << 2;
 
-pub fn block_descriptor_entry(addr: u64, mair_index: u64, additional_flags: u64) -> u64 {
+/// Disallow EL1 Execution.
-    let pxn = 0 << 53; // allow EL1 execution
+const PXN: u64 = 1 << 53;
-    let uxn = 0 << 54; // allow EL0 execution
 
-    (addr & 0x0000_FFFF_FFE0_0000)
+/// Disallow EL0 Execution.
+const UXN: u64 = 1 << 54;
+
+const GRANULARITY: usize = 4 * 1024;
+const TABLE_ENTRY_COUNT: usize = GRANULARITY / size_of::<u64>(); // 2MiB
+const LEVEL2_BLOCK_SIZE: usize = TABLE_ENTRY_COUNT * GRANULARITY;
+
+const MAX_PAGE_COUNT: usize = 1 * 1024 * 1024 * 1024 / GRANULARITY;
+#[repr(align(4096))]
+pub struct PageTable([u64; TABLE_ENTRY_COUNT]);
+
+#[no_mangle]
+pub static mut TRANSLATIONTABLE_TTBR0: PageTable = PageTable([0; 512]);
+pub static mut TRANSLATIONTABLE_TTBR0_L2_0: PageTable = PageTable([0; 512]);
+
+static mut PAGING_BITMAP: [u64; MAX_PAGE_COUNT / 64] = [0; MAX_PAGE_COUNT / 64];
+
+pub fn init_translation_table() {
+    unsafe {
+        TRANSLATIONTABLE_TTBR0.0[0] =
+            table_descriptor_entry(&raw mut TRANSLATIONTABLE_TTBR0_L2_0 as usize);
+        println!("{}", &raw mut TRANSLATIONTABLE_TTBR0_L2_0 as u64);
+        println!("{}", TRANSLATIONTABLE_TTBR0.0[0] & 0x0000_FFFF_FFFF_F000);
+
+        for i in 0..512 {
+            let addr = 0x0 + (i * LEVEL2_BLOCK_SIZE);
+
+            if addr < &_data as *const _ as usize {
+                let _ = alloc_block_l2(
+                    addr,
+                    &TRANSLATIONTABLE_TTBR0,
+                    EL0_ACCESSIBLE | READ_ONLY | NORMAL_MEM,
+                );
+            } else if addr < &__kernel_end as *const _ as usize {
+                let _ = alloc_block_l2(addr, &TRANSLATIONTABLE_TTBR0, WRITABLE | UXN | NORMAL_MEM);
+            } else if addr < PERIPHERAL_BASE {
+                let _ = alloc_block_l2(
+                    addr,
+                    &TRANSLATIONTABLE_TTBR0,
+                    EL0_ACCESSIBLE | WRITABLE | PXN | NORMAL_MEM,
+                );
+            } else {
+                let _ = alloc_block_l2(
+                    addr,
+                    &TRANSLATIONTABLE_TTBR0,
+                    EL0_ACCESSIBLE | WRITABLE | UXN | PXN | DEVICE_MEM,
+                );
+            };
+        }
+        println!("Done");
+    }
+}
+
+pub fn alloc_page() -> Result<usize, NovaError> {
+    find_unallocated_page()
+}
+
+fn find_unallocated_page() -> Result<usize, NovaError> {
+    for (i, entry) in unsafe { PAGING_BITMAP }.iter().enumerate() {
+        if *entry != u64::MAX {
+            for offset in 0..64 {
+                if entry >> offset & 0b1 == 0 {
+                    return Ok((i * 64 + offset) * GRANULARITY);
+                }
+            }
+        }
+    }
+    Err(NovaError::Paging)
+}
+
+pub fn alloc_block_l2(
+    virtual_addr: usize,
+    base_table: &PageTable,
+    additional_flags: u64,
+) -> Result<(), NovaError> {
+    let physical_address = find_unallocated_block_l2()?;
+
+    let l2_off = virtual_addr / GRANULARITY / TABLE_ENTRY_COUNT;
+    let l1_off = l2_off / TABLE_ENTRY_COUNT;
+
+    let l2_table =
+        unsafe { &mut *((base_table.0[l1_off] & 0x0000_FFFF_FFFF_F000) as *mut PageTable) };
+
+    let new_entry = create_block_descriptor_entry(physical_address, additional_flags);
+
+    l2_table.0[l2_off] = new_entry;
+
+    allocate_block_l2(physical_address);
+
+    Ok(())
+}
+
+fn find_unallocated_block_l2() -> Result<usize, NovaError> {
+    let mut count = 0;
+    for (i, entry) in unsafe { PAGING_BITMAP }.iter().enumerate() {
+        if *entry == 0 {
+            count += 1;
+        } else {
+            count = 0;
+        }
+
+        if count == 8 {
+            return Ok((i - 7) * 64 * GRANULARITY);
+        }
+    }
+    Err(NovaError::Paging)
+}
+
+fn allocate_block_l2(physical_address: usize) {
+    let page = physical_address / GRANULARITY;
+    for i in 0..8 {
+        unsafe { PAGING_BITMAP[(page / 64) + i] = MAX };
+    }
+}
+
+fn create_block_descriptor_entry(addr: usize, additional_flags: u64) -> u64 {
+    let pxn = 0 << 53; // Privileged execute never
+    let uxn = 0 << 54; // Unprivileged execute never
+
+    (addr as u64 & 0x0000_FFFF_FFE0_0000)
         | BLOCK
-        | mair_index
         | ACCESS_FLAG
         | pxn
         | uxn
@@ -62,6 +156,6 @@ pub fn block_descriptor_entry(addr: u64, mair_index: u64, additional_flags: u64)
         | additional_flags
 }
 
-pub fn table_descriptor_entry(addr: u64) -> u64 {
+pub fn table_descriptor_entry(addr: usize) -> u64 {
-    0 | (addr & 0x0000_FFFF_FFFF_F000) | TABLE
+    0 | (addr as u64 & 0x0000_FFFF_FFFF_F000) | TABLE
 }

src/configuration.rs

@@ -17,21 +17,17 @@ pub static SCTLR_EL1_CONF: u64 = SCTLR_EL1_MMU_ENABLED
     | SCTLR_EL1_RES
     | SCTLR_EL1_SPAN;
 
-// TODO: Document magic numbers
+const TG0: u64 = 0b00 << 14; // 4KB granularity EL0
+const T0SZ: u64 = 25; // 25 Bits of TTBR select -> 39 Bits of VA
+const SH0: u64 = 0b11 << 12; // Inner shareable
 
-const TG0: u64 = 0b00 << 14;
+const TG1: u64 = 0b10 << 30; // 4KB granularity EL1
-const TG1: u64 = 0b10 << 30;
+const T1SZ: u64 = 25 << 16; // 25 Bits of TTBR select -> 39 Bits of VA
+const EPD1: u64 = 0b1 << 23; // Trigger translation fault when using TTBR1_EL1
+const SH1: u64 = 0b11 << 28; // Inner sharable
 
-const T0SZ: u64 = 27;
+const IPS: u64 = 0b000 << 32; // 32 bits of PA space -> up to 4GiB
-const T1SZ: u64 = 27 << 16;
+const AS: u64 = 0b1 << 36; // configure an ASID size of 16 bits
 
-const SH0: u64 = 0b11 << 12;
-const SH1: u64 = 0b11 << 28;
-
-const IPS: u64 = 0b000 << 32;
-const EPD1: u64 = 0b1 << 23;
-
-const AS: u64 = 0b1 << 36;
-const TBI0: u64 = 0b1 << 38;
 #[no_mangle]
-pub static TCR_EL1_CONF: u64 = IPS | TG0 | TG1 | T0SZ | T1SZ | SH0 | SH1 | EPD1 | AS | TBI0;
+pub static TCR_EL1_CONF: u64 = IPS | TG0 | TG1 | T0SZ | T1SZ | SH0 | SH1 | EPD1 | AS;

src/lib.rs

@@ -14,7 +14,7 @@ use heap::Heap;
 
 use crate::{interrupt_handlers::initialize_interrupt_handler, logger::DefaultLogger};
 
-static PERIPHERAL_BASE: u32 = 0x3F00_0000;
+static PERIPHERAL_BASE: usize = 0x3F00_0000;
 
 unsafe extern "C" {
     unsafe static mut __heap_start: u8;

src/main.rs

@@ -19,7 +19,6 @@ use nova::{
     framebuffer::{FrameBuffer, BLUE, GREEN, RED},
     get_current_el, init_heap,
     interrupt_handlers::{enable_irq_source, IRQSource},
-    log,
     peripherals::{
         gpio::{
             blink_gpio, gpio_pull_up, set_falling_edge_detect, set_gpio_function, GPIOFunction,
@@ -128,12 +127,12 @@ pub extern "C" fn el0() -> ! {
 
     loop {
         let temp = mailbox::read_soc_temp([0]).unwrap();
-        log!("{} °C", temp[1] / 1000);
+        println!("{} °C", temp[1] / 1000);
 
         blink_gpio(SpecificGpio::OnboardLed as u8, 500);
 
         let b = Box::new([1, 2, 3, 4]);
-        log!("{:?}", b);
+        println!("{:?}", b);
     }
 }
 

src/pi3/power_management.rs

@@ -3,7 +3,7 @@ use core::ptr::{read_volatile, write_volatile};
 use crate::PERIPHERAL_BASE;
 
 /// Power Management Base
-static PM_BASE: u32 = PERIPHERAL_BASE + 0x10_0000;
+static PM_BASE: u32 = PERIPHERAL_BASE as u32 + 0x10_0000;
 static PM_RSTC: u32 = PM_BASE + 0x1c;
 static PM_WDOG: u32 = PM_BASE + 0x24;
 

src/vector.S

@@ -56,7 +56,7 @@ el2_to_el1:
 
     adrp x0, SCTLR_EL1_CONF
     ldr  x1, [x0, :lo12:SCTLR_EL1_CONF]
-    msr SCTLR_EL1, x0
+    msr SCTLR_EL1, x1
 
     isb
 
@@ -74,18 +74,23 @@ el2_to_el1:
 .align 4
 .global configure_mmu_el1
 configure_mmu_el1:
+    // Configure MMU
     adrp x0, TCR_EL1_CONF
     ldr  x1, [x0, :lo12:TCR_EL1_CONF]
-    msr TCR_EL1, x0
+    msr TCR_EL1, x1
     isb
 
+    // MAIR0: Normal Mem.
+    // MAIR1: Device Mem.
     mov x0, #0x04FF
     msr MAIR_EL1, x0
     isb
 
-    ldr x0, =__translation_table_l1_start
+    // Configure translation table
-    msr TTBR0_EL1, x0
+    adrp x0, TRANSLATIONTABLE_TTBR0
-    msr TTBR1_EL1, x0
+    add  x1, x0, :lo12:TRANSLATIONTABLE_TTBR0
+    msr TTBR0_EL1, x1
+    msr TTBR1_EL1, x1
 
     tlbi vmalle1
     dsb ish
@@ -210,10 +215,3 @@ synchronous_interrupt_no_el_change:
     add sp, sp, #176
 
     eret
-
-.align 4
-.global pan
-pan:
-    mov x0, #0
-    msr S3_0_C4_C2_3, x0
-    ret

workspace/nova_error/src/lib.rs

@@ -8,4 +8,5 @@ pub enum NovaError {
     Mailbox,
     HeapFull,
     EmptyHeapSegmentNotAllowed,
+    Paging,
 }