Kernel, libc: Implement mprotect() and use proper PROT_* values

kernel/include/sys/Syscall.h

@@ -17,6 +17,7 @@
 #define SYS_seek 12
 #define SYS_exec 13
 #define SYS_fcntl 14
+#define SYS_mprotect 15
 
 namespace Syscall
 {
@@ -32,7 +33,7 @@ void sys_write(Context* context, int fd, size_t size, const char* addr);
 void sys_paint(Context* context, uint64_t x, uint64_t y, uint64_t w, uint64_t h, uint64_t col);
 void sys_rand(Context* context);
 void sys_gettid(Context* context);
-void sys_mmap(Context* context, void* address, size_t size, int flags);
+void sys_mmap(Context* context, void* address, size_t size, int prot);
 void sys_munmap(Context* context, void* address, size_t size);
 void sys_open(Context* context, const char* filename, int flags);
 void sys_read(Context* context, int fd, size_t size, char* buffer);
@@ -40,3 +41,4 @@ void sys_close(Context* context, int fd);
 void sys_seek(Context* context, int fd, long offset, int whence);
 void sys_exec(Context* context, const char* pathname);
 void sys_fcntl(Context* context, int fd, int command, uintptr_t arg);
+void sys_mprotect(Context* context, void* address, size_t size, int prot);

kernel/src/sys/Syscall.cpp

@@ -26,6 +26,7 @@ void Syscall::entry(Context* context)
     case SYS_seek: sys_seek(context, (int)context->rdi, (long)context->rsi, (int)context->rdx); break;
     case SYS_exec: sys_exec(context, (const char*)context->rdi); break;
     case SYS_fcntl: sys_fcntl(context, (int)context->rdi, (int)context->rsi, context->rdx); break;
+    case SYS_mprotect: sys_mprotect(context, (void*)context->rdi, context->rsi, (int)context->rdx); break;
     default: context->rax = -ENOSYS; break;
     }
     VMM::exit_syscall_context();

kernel/src/sys/mem.cpp

@@ -8,9 +8,30 @@
 #include "misc/utils.h"
 #include <stddef.h>
 
+#define MAP_READ 1
+#define MAP_WRITE 2
+#define MAP_NONE 0
+
 #define MAP_FAIL(errno) 0xffffffffffffff00 | (unsigned char)(errno)
 
-void sys_mmap(Context* context, void* address, size_t size, int flags)
+static const char* format_prot(int prot)
+{
+    static char prot_string[3];
+    prot_string[2] = 0;
+    prot_string[0] = ((prot & MAP_READ) > 0) ? 'r' : '-';
+    prot_string[1] = ((prot & MAP_WRITE) > 0) ? 'w' : '-';
+    return prot_string;
+}
+
+static int mman_flags_from_prot(int prot)
+{
+    prot &= 0b11;
+    if (prot == MAP_NONE) return 0;
+    if ((prot & MAP_WRITE) > 0) return MAP_USER | MAP_READ_WRITE;
+    return MAP_USER;
+}
+
+void sys_mmap(Context* context, void* address, size_t size, int prot)
 {
     if (size < PAGE_SIZE)
     {
@@ -24,12 +45,10 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
         context->rax = MAP_FAIL(EINVAL);
         return;
     }
-    int real_flags = MAP_USER;
+    int real_flags = mman_flags_from_prot(prot);
-    if (flags & MAP_READ_WRITE) real_flags |= MAP_READ_WRITE;
     if (address)
     {
-        kdbgln("mmap(): %ld pages at address %p, %s", size / PAGE_SIZE, address,
+        kdbgln("mmap(): %ld pages at address %p, %s", size / PAGE_SIZE, address, format_prot(prot));
-               real_flags & MAP_READ_WRITE ? "rw" : "ro");
         if (VMM::get_physical((uint64_t)address) != (uint64_t)-1) // Address is already used.
         {
             kwarnln("attempt to map an already mapped address");
@@ -52,8 +71,7 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
             return;
         }
     }
-    kdbgln("mmap(): %ld pages at any address, %s", Utilities::get_blocks_from_size(PAGE_SIZE, size),
+    kdbgln("mmap(): %ld pages at any address, %s", Utilities::get_blocks_from_size(PAGE_SIZE, size), format_prot(prot));
-           real_flags & MAP_READ_WRITE ? "rw" : "ro");
     void* result = MemoryManager::get_pages(Utilities::get_blocks_from_size(PAGE_SIZE, size), real_flags);
     if (result)
     {
@@ -103,3 +121,42 @@ void sys_munmap(Context* context, void* address, size_t size)
     context->rax = 0;
     return;
 }
+
+void sys_mprotect(Context* context, void* address, size_t size, int prot)
+{
+    kdbgln("mprotect(): attempting to protect %p with %s", address, format_prot(prot));
+
+    if (size < PAGE_SIZE)
+    {
+        kwarnln("mprotect() failed: size is too small");
+        context->rax = -EINVAL;
+        return;
+    }
+    if (size % PAGE_SIZE)
+    {
+        kwarnln("mprotect() failed: size is not a multiple of PAGE_SIZE");
+        context->rax = -EINVAL;
+        return;
+    }
+    if (!address)
+    {
+        kwarnln("mprotect() failed: attempted to unmap page 0");
+        context->rax = -EINVAL;
+        return;
+    }
+
+    uint64_t flags = VMM::get_flags((uint64_t)address);
+    if (!(flags & MAP_USER))
+    {
+        kwarnln("mprotect() failed: attempted to protect a non-existent or kernel page");
+        context->rax = -EINVAL;
+        return;
+    }
+
+    uint64_t offset = (uint64_t)address % PAGE_SIZE;
+    MemoryManager::protect((void*)((uint64_t)address - offset), Utilities::get_blocks_from_size(PAGE_SIZE, size),
+                           mman_flags_from_prot(prot));
+    kdbgln("mprotect() succeeded");
+    context->rax = 0;
+    return;
+}

libs/libc/include/sys/mman.h

@@ -7,7 +7,9 @@
 /* Address returned by mmap when it fails. */
 #define MAP_FAILED (void*)-1
 
-#define PROT_READ_WRITE 1
+#define PROT_NONE 0
+#define PROT_READ 1
+#define PROT_WRITE 2
 
 #define PAGE_SIZE 4096
 
@@ -24,6 +26,9 @@ extern "C"
      * address space. */
     int munmap(void* addr, size_t size);
 
+    /* Protects size bytes of memory according to the prot argument. */
+    int mprotect(void* addr, size_t size, int prot);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/src/bits/bindings.c

@@ -13,7 +13,7 @@ int liballoc_unlock()
 
 void* liballoc_alloc(size_t size)
 {
-    void* result = mmap(NULL, size * PAGE_SIZE, PROT_READ_WRITE, 0, 0, 0);
+    void* result = mmap(NULL, size * PAGE_SIZE, PROT_READ | PROT_WRITE, 0, 0, 0);
     if (result == MAP_FAILED) return 0;
     return (void*)result;
 }