Load a very simple ELF and launch it in usermode

arch/x86_64/src/idt.rs

@@ -60,6 +60,7 @@ pub unsafe fn init() {
 
     // Set syscall function
     IDT[0x80].set_func(syscall::syscall);
+    IDT[0x80].set_flags(IDT_PRESENT | IDT_RING_3 | IDT_INTERRUPT);
 
     dtables::lidt(&IDTR);
 }

arch/x86_64/src/interrupt/syscall.rs

@@ -1,22 +1,29 @@
 #[naked]
 pub unsafe extern fn syscall() {
-    extern {
-        fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+    #[inline(never)]
+    unsafe fn inner() {
+        extern {
+            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+        }
+
+        let mut a;
+        {
+            let b;
+            let c;
+            let d;
+            let e;
+            let f;
+            asm!("xchg bx, bx" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
+                : : : "intel", "volatile");
+
+            a = syscall(a, b, c, d, e, f);
+        }
+
+        asm!("xchg bx, bx" : : "{rax}"(a) : : "intel", "volatile");
     }
 
-    let a;
-    let b;
-    let c;
-    let d;
-    let e;
-    let f;
-    asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
-        : : : "intel", "volatile");
+    inner();
 
-    let a = syscall(a, b, c, d, e, f);
-
-    asm!("" : : "{rax}"(a) : : "intel", "volatile");
-
-    // Pop scratch registers, error code, and return
+    // Interrupt return
     asm!("iretq" : : : : "intel", "volatile");
 }

arch/x86_64/src/lib.rs

@@ -17,7 +17,7 @@ extern crate hole_list_allocator as allocator;
 extern crate bitflags;
 extern crate ransid;
 extern crate spin;
-extern crate x86;
+pub extern crate x86;
 
 /// Print to console
 #[macro_export]

arch/x86_64/src/paging/mapper.rs

@@ -46,6 +46,15 @@ impl Mapper {
         self.map_to(page, frame, flags)
     }
 
+    /// Update flags for a page
+    pub fn remap(&mut self, page: Page, flags: EntryFlags) {
+        let mut p3 = self.p4_mut().next_table_mut(page.p4_index()).expect("failed to remap: no p3");
+        let mut p2 = p3.next_table_mut(page.p3_index()).expect("failed to remap: no p2");
+        let mut p1 = p2.next_table_mut(page.p2_index()).expect("failed to remap: no p1");
+        let frame = p1[page.p1_index()].pointed_frame().expect("failed to remap: not mapped");
+        p1[page.p1_index()].set(frame, flags | entry::PRESENT);
+    }
+
     /// Identity map a frame
     pub fn identity_map(&mut self, frame: Frame, flags: EntryFlags) {
         let page = Page::containing_address(VirtualAddress::new(frame.start_address().get()));

arch/x86_64/src/paging/table.rs

@@ -66,7 +66,7 @@ impl<L> Table<L> where L: HierarchicalLevel {
             assert!(!self[index].flags().contains(HUGE_PAGE),
                     "mapping code does not support huge pages");
             let frame = allocate_frame().expect("no frames available");
-            self[index].set(frame, PRESENT | WRITABLE);
+            self[index].set(frame, PRESENT | WRITABLE | USER_ACCESSIBLE /* Allow users to go down the page table, implement permissions at the page level */);
             self.next_table_mut(index).unwrap().zero();
         }
         self.next_table_mut(index).unwrap()

arch/x86_64/src/start.rs

@@ -137,28 +137,6 @@ pub unsafe extern fn kstart() -> ! {
     kmain();
 }
 
-unsafe fn usermode(ip: usize, sp: usize) {
-    // Test usermode
-    asm!("xchg bx, bx
-        mov rax, 0x2B
-        mov ds, ax
-        mov es, ax
-        mov fs, ax
-        mov gs, ax
-
-        push rax
-        push rbx
-        pushfq
-        mov rax, 0x23
-        push rax
-        push rcx
-        iretq"
-        :
-        : "{rbx}"(sp), "{rcx}"(ip)
-        : "rax", "rbx", "rcx", "sp"
-        : "intel", "volatile");
-}
-
 /// Entry to rust for an AP
 pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
     {
@@ -223,3 +201,25 @@ pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
 
     kmain_ap(ap_number);
 }
+
+pub unsafe fn usermode(ip: usize, sp: usize) {
+    // Test usermode
+    asm!("xchg bx, bx
+        mov rax, 0x2B
+        mov ds, ax
+        mov es, ax
+        mov fs, ax
+        mov gs, ax
+
+        push rax
+        push rbx
+        pushfq
+        mov rax, 0x23
+        push rax
+        push rcx
+        iretq"
+        :
+        : "{rbx}"(sp), "{rcx}"(ip)
+        : "rax", "rbx", "rcx", "sp"
+        : "intel", "volatile");
+}

init/main.asm

@@ -0,0 +1,20 @@
+[bits 64]
+section     .text
+global      _start                              ;must be declared for linker (ld)
+
+_start:                                         ;tell linker entry point
+
+    xchg    bx, bx
+    mov     rdx,len                             ;message length
+    mov     rcx,msg                             ;message to write
+    mov     rbx,1                               ;file descriptor (stdout)
+    mov     rax,4                               ;system call number (sys_write)
+    int     0x80                                ;call kernel
+
+    mov     rax,1                               ;system call number (sys_exit)
+    int     0x80                                ;call kernel
+
+section     .data
+
+msg     db  'Hello, world!',0xa                 ;our dear string
+len     equ $ - msg                             ;length of our dear string

kernel/elf.rs

@@ -1,8 +1,8 @@
 //! ELF executables
 
-use collections::{String, Vec};
+use collections::String;
 
-use core::{ptr, str};
+use core::str;
 
 #[cfg(target_arch = "x86")]
 use goblin::elf32::{header, program_header};
@@ -10,9 +10,15 @@ use goblin::elf32::{header, program_header};
 #[cfg(target_arch = "x86_64")]
 use goblin::elf64::{header, program_header};
 
+use arch::externs::{memcpy, memset};
+use arch::paging::{entry, ActivePageTable, Page, VirtualAddress};
+use arch::start::usermode;
+use arch::x86::tlb;
+
 /// An ELF executable
 pub struct Elf<'a> {
     pub data: &'a [u8],
+    header: &'a header::Header
 }
 
 impl<'a> Elf<'a> {
@@ -25,29 +31,125 @@ impl<'a> Elf<'a> {
         } else if data.get(header::EI_CLASS) != Some(&header::ELFCLASS) {
             Err(format!("Elf: Invalid architecture: {:?} != {:?}", data.get(header::EI_CLASS), header::ELFCLASS))
         } else {
-            Ok(Elf { data: data })
+            Ok(Elf {
+                data: data,
+                header: unsafe { &*(data.as_ptr() as usize as *const header::Header) }
+            })
         }
     }
 
-    pub unsafe fn load_segments(&self) -> Vec<program_header::ProgramHeader> {
-        let mut segments = Vec::new();
-
-        let header = &*(self.data.as_ptr() as usize as *const header::Header);
-
-        for i in 0..header.e_phnum {
-            let segment = ptr::read((self.data.as_ptr() as usize + header.e_phoff as usize + i as usize * header.e_phentsize as usize) as *const program_header::ProgramHeader);
-
-            if segment.p_type == program_header::PT_LOAD || segment.p_type == program_header::PT_TLS {
-                segments.push(segment);
-            }
+    pub fn segments(&'a self) -> ElfSegments<'a> {
+        ElfSegments {
+            data: self.data,
+            header: self.header,
+            i: 0
         }
-
-        segments
     }
 
     /// Get the entry field of the header
-    pub unsafe fn entry(&self) -> usize {
-        let header = &*(self.data.as_ptr() as usize as *const header::Header);
-        header.e_entry as usize
+    pub fn entry(&self) -> usize {
+        self.header.e_entry as usize
+    }
+
+    /// Test function to run. Remove and replace with proper syscall
+    pub fn run(self) {
+        let mut active_table = unsafe { ActivePageTable::new() };
+
+        for segment in self.segments() {
+            println!("Segment {:X} flags {:X} off {:X} virt {:X} phys {:X} file {} mem {} align {}",
+                        segment.p_type, segment.p_flags, segment.p_offset,
+                        segment.p_vaddr, segment.p_paddr, segment.p_filesz,
+                        segment.p_memsz, segment.p_align);
+
+            if segment.p_type == program_header::PT_LOAD {
+                let start_page = Page::containing_address(VirtualAddress::new(segment.p_vaddr as usize));
+                let end_page = Page::containing_address(VirtualAddress::new((segment.p_vaddr + segment.p_memsz) as usize));
+
+                for page in Page::range_inclusive(start_page, end_page) {
+                    active_table.map(page, entry::NO_EXECUTE | entry::WRITABLE);
+                }
+
+                unsafe {
+                    // Update the page table
+                    tlb::flush_all();
+
+                    // Copy file data
+                    memcpy(segment.p_vaddr as *mut u8,
+                            (self.data.as_ptr() as usize + segment.p_offset as usize) as *const u8,
+                            segment.p_filesz as usize);
+                    // Set BSS
+                    memset((segment.p_vaddr + segment.p_filesz) as *mut u8,
+                            0,
+                            (segment.p_memsz - segment.p_filesz) as usize);
+                }
+
+                let mut flags = entry::NO_EXECUTE | entry::USER_ACCESSIBLE;
+
+                if segment.p_flags & program_header::PF_R == program_header::PF_R {
+                    flags.insert(entry::PRESENT);
+                }
+
+                // W ^ X. If it is executable, do not allow it to be writable, even if requested
+                if segment.p_flags & program_header::PF_X == program_header::PF_X {
+                    flags.remove(entry::NO_EXECUTE);
+                } else if segment.p_flags & program_header::PF_W == program_header::PF_W {
+                    flags.insert(entry::WRITABLE);
+                }
+
+                for page in Page::range_inclusive(start_page, end_page) {
+                    println!("{:X}: {:?}", page.start_address().get(), flags);
+                    active_table.remap(page, flags);
+                }
+
+                unsafe {
+                    // Update the page table
+                    tlb::flush_all();
+                }
+            }
+        }
+
+        unsafe {
+            // Map stack
+            let start_page = Page::containing_address(VirtualAddress::new(0x80000000));
+            let end_page = Page::containing_address(VirtualAddress::new(0x80000000 + 64*1024 - 1));
+
+            for page in Page::range_inclusive(start_page, end_page) {
+                active_table.map(page, entry::NO_EXECUTE | entry::WRITABLE | entry::USER_ACCESSIBLE);
+            }
+
+            // Update the page table
+            tlb::flush_all();
+
+            // Clear stack
+            memset(0x80000000 as *mut u8, 0, 64 * 1024);
+
+            // Go to usermode
+            usermode(self.entry(), 0x80000000 + 64*1024 - 256);
+        }
+    }
+}
+
+pub struct ElfSegments<'a> {
+    data: &'a [u8],
+    header: &'a header::Header,
+    i: usize
+}
+
+impl<'a> Iterator for ElfSegments<'a> {
+    type Item = &'a program_header::ProgramHeader;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.i < self.header.e_phnum as usize {
+            let item = unsafe {
+                &* ((
+                        self.data.as_ptr() as usize
+                        + self.header.e_phoff as usize
+                        + self.i * self.header.e_phentsize as usize
+                    ) as *const program_header::ProgramHeader)
+            };
+            self.i += 1;
+            Some(item)
+        } else {
+            None
+        }
     }
 }

kernel/lib.rs

@@ -133,6 +133,9 @@ pub extern fn kmain() {
     let pid = syscall::getpid();
     println!("BSP: {:?}", pid);
 
+    let elf = elf::Elf::from(include_bytes!("../init/main")).expect("could not load elf");
+    elf.run();
+
     /*
     if let Ok(_context_lock) = context::contexts_mut().spawn(context_test) {
         print!("Spawned context\n");