x86_64: various fixes for no-execute pages

Author: jewelcodes

src/platform/x86_64/apic/apic.c

@@ -34,15 +34,9 @@ int apicInit() {
         while(1);
     }
 
-    // check for PAE/NX
+    // check for syscall/sysret instructions
     memset(&regs, 0, sizeof(CPUIDRegisters));
     readCPUID(0x80000001, &regs);
-    if(!(regs.edx & (1 << 20))) {
-        KERROR("CPU doesn't support PAE/NX\n");
-        while(1);
-    }
-
-    // and syscall/sysret instructions
     if(!(regs.edx & (1 << 11))) {
         KERROR("CPU doesn't support fast syscall/sysret\n");
         while(1);

src/platform/x86_64/apic/smp.c

@@ -76,9 +76,6 @@ void smpCPUInfoSetup() {
     readCPUID(1, &regs);
     uint8_t apicID = regs.ebx >> 24;
 
-    // enable NX
-    writeMSR(MSR_EFER, readMSR(MSR_EFER) | MSR_EFER_NX_ENABLE);
-
     // enable fast fxsave/fxrstor if supported
     memset(&regs, 0, sizeof(CPUIDRegisters));
     readCPUID(0x80000001, &regs);

src/platform/x86_64/apic/smpstub.asm

@@ -59,6 +59,14 @@ times 0x100 - ($-$$) nop
     mov fs, rax
     mov gs, rax
 
+    ; enable NX - this is necessary here because the pages mapping the stack
+    ; are marked as no-execute, so we cannot wait until the C code to do this
+    ; else we get unhandled page faults :)
+    mov ecx, 0xC0000080
+    rdmsr
+    or eax, 0x800
+    wrmsr
+
     mov rax, 0x1FF0         ; top of stack pointer
     mov rsp, [rax]
     mov rbp, rsp

src/platform/x86_64/cpu/paging.c

@@ -20,9 +20,19 @@ static uint64_t *kernelPagingRoot;  // pml4 -- PHYSICAL ADDRESS
  */
 
 int platformPagingSetup() {
-    // identity map the lower memory
-    // this is already true but we need to replace the paging structs built
-    // by the boot loader
+    // check for PAE/NX
+    CPUIDRegisters regs;
+    memset(&regs, 0, sizeof(CPUIDRegisters));
+    readCPUID(0x80000001, &regs);
+    if(!(regs.edx & (1 << 20))) {
+        KERROR("CPU doesn't support PAE/NX\n");
+        while(1);
+    }
+
+    // enable no-execute pages
+    writeMSR(MSR_EFER, readMSR(MSR_EFER) | MSR_EFER_NX_ENABLE);
+
+    // map physical memory into the higher half
     uint64_t *pml4 = (uint64_t *)pmmAllocate();     // 512 GiB per entry
     uint64_t *pdp = (uint64_t *)pmmAllocate();      // 1 GiB per entry
 
@@ -58,7 +68,7 @@ int platformPagingSetup() {
     writeCR3((uint64_t)pml4);
 
     ttyRemapFramebuffer();
-    KDEBUG("kernel paging structures created, identity mapped %d GiB\n", KERNEL_BASE_MAPPED);
+    KDEBUG("kernel paging structures created, mapped %d GiB at 0x%X\n", KERNEL_BASE_MAPPED, KERNEL_MMIO_BASE);
     kernelPagingRoot = pml4;
     return 0;
 }
@@ -137,7 +147,7 @@ uintptr_t platformGetPage(int *flags, uintptr_t addr) {
     if(!(ptEntry & PT_PAGE_NXE)) *flags |= PLATFORM_PAGE_EXEC;
     if(ptEntry & PT_PAGE_NO_CACHE) *flags |= PLATFORM_PAGE_NO_CACHE;
 
-    return (ptEntry & ~(PAGE_SIZE-1)) | offset;
+    return (ptEntry & ~(PAGE_SIZE-1) & ~(PT_PAGE_NXE)) | offset;
 }
 
 /* platformMapPage(): maps a physical address to a logical address
@@ -205,7 +215,7 @@ uintptr_t platformMapPage(uintptr_t logical, uintptr_t physical, int flags) {
     if(flags & PLATFORM_PAGE_PRESENT) parsedFlags |= PT_PAGE_PRESENT;
     if(flags & PLATFORM_PAGE_WRITE) parsedFlags |= PT_PAGE_RW;
     if(flags & PLATFORM_PAGE_USER) parsedFlags |= PT_PAGE_USER;
-    if(!flags & PLATFORM_PAGE_EXEC) parsedFlags |= PT_PAGE_NXE;
+    if(!(flags & PLATFORM_PAGE_EXEC)) parsedFlags |= PT_PAGE_NXE;
     if(flags & PLATFORM_PAGE_NO_CACHE) parsedFlags |= PT_PAGE_NO_CACHE | PT_PAGE_WRITE_THROUGH;
 
     pt[ptIndex] = physical | parsedFlags;