vfs: Provide drivers with secure copies of caller buffers

Fixes #45.

1 files changed, 25 insertions, 5 deletions

diff --git a/src/lib/vfs.zig b/src/lib/vfs.zig
index d9a7b90..b6646bf 100644
--- a/src/lib/vfs.zig
+++ b/src/lib/vfs.zig
@@ -4,6 +4,7 @@
 
 const std = @import("std");
 
+const paging = @import("paging.zig");
 const process = @import("process.zig");
 const sysexchange = @import("sysexchange.zig");
 
@@ -133,10 +134,15 @@ pub const ResourceDescriptor = struct {
         return switch (self.inode.resource) {
             .stream => |stream| {
                 const driver = process.latestThread(self.inode.pid).?;
+                const copy = try driver.copyBuffer(buffer);
 
                 const readFn = stream.readFn orelse return Error.ReadNotSupported;
                 proc.state = .suspended;
-                try call(driver, readFn, .{ buffer.ptr, buffer.len }, .{
+                try call(driver, readFn, .{ copy.ptr, copy.len }, .{
+                    .cleanupFn = moveBack,
+                    .buffer = buffer,
+                    .copy = copy,
+                }, .{
                     .hookFn = crossProcessReturn,
                     .context = proc,
                 });
@@ -150,10 +156,11 @@ pub const ResourceDescriptor = struct {
         return switch (self.inode.resource) {
             .stream => |stream| {
                 const driver = process.latestThread(self.inode.pid).?;
+                const copy = try driver.copyBytes(bytes);
 
                 const writeFn = stream.writeFn orelse return Error.WriteNotSupported;
                 proc.state = .suspended;
-                try call(driver, writeFn, .{ bytes.ptr, bytes.len }, .{
+                try call(driver, writeFn, .{ copy.ptr, copy.len }, null, .{
                     .hookFn = crossProcessReturn,
                     .context = proc,
                 });
@@ -162,6 +169,19 @@ pub const ResourceDescriptor = struct {
             else => Error.WriteNotSupported,
         };
     }
+
+    fn moveBack(driver: *const process.Info, buffer: []u8, copy: []const u8) void {
+        paging.setUserMemoryAccess(true);
+        defer paging.setUserMemoryAccess(false);
+
+        @memcpy(buffer, copy);
+
+        var addr = @intFromPtr(copy.ptr);
+        const limit = addr + copy.len;
+        while (addr < limit) : (addr += paging.page_size) {
+            driver.page_table.unmapEntry(addr);
+        }
+    }
 };
 
 pub const UserInfo = union(enum) {
@@ -222,7 +242,7 @@ pub fn open(proc: *process.Info, path: []const u8, pid: u16, data: usize) !Resou
             const driver = process.latestThread(node.data.pid).?;
 
             proc.state = .suspended;
-            try call(driver, hook.callback, .{ pid, data }, .{
+            try call(driver, hook.callback, .{ pid, data }, null, .{
                 .hookFn = crossProcessReturn,
                 .context = proc,
             });
@@ -235,9 +255,9 @@ pub fn openZ(proc: *process.Info, path_c: [*:0]const u8, pid: u16, data: usize)
     return open(proc, mem.sliceTo(path_c, 0), pid, data);
 }
 
-fn call(proc: *process.Info, function: *const anyopaque, args: anytype, termHook: ?process.Info.TermHook) !noreturn {
+fn call(proc: *process.Info, function: *const anyopaque, args: anytype, cleanup_hook: ?process.Info.CleanupHook, term_hook: ?process.Info.TermHook) !noreturn {
     const callback_thread = try proc.createThread(null);
-    callback_thread.call(@intFromPtr(function), args, termHook);
+    callback_thread.call(@intFromPtr(function), args, cleanup_hook, term_hook);
 }
 
 fn crossProcessReturn(context: *anyopaque, driver: *const process.Info) void {