vfs: Provide drivers with secure copies of caller buffers

Fixes #45.

1 files changed, 56 insertions, 1 deletions

diff --git a/src/lib/process.zig b/src/lib/process.zig
index c155243..aa3568c 100644
--- a/src/lib/process.zig
+++ b/src/lib/process.zig
@@ -58,11 +58,18 @@ pub const Info = struct {
     pages: []align(paging.page_size) u8,
     stack: []align(paging.page_size) u8,
     pc: usize,
+    cleanup_hook: ?CleanupHook,
     term_hook: ?TermHook,
     page_table: *paging.Table,
     state: State,
     rds: std.AutoArrayHashMap(usize, vfs.ResourceDescriptor),
 
+    pub const CleanupHook = struct {
+        cleanupFn: *const fn (proc: *const Info, buffer: []u8, copy: []const u8) void,
+        buffer: []u8,
+        copy: []const u8,
+    };
+
     pub const TermHook = struct {
         hookFn: *const fn (context: *anyopaque, proc: *const Info) void,
         context: *anyopaque,
@@ -122,6 +129,7 @@ pub const Info = struct {
             .pages = self.pages,
             .stack = stack,
             .pc = self.pc,
+            .cleanup_hook = null,
             .term_hook = null,
             .page_table = self.page_table,
             .state = .suspended,
@@ -135,7 +143,7 @@ pub const Info = struct {
         return &proc_node.data;
     }
 
-    pub fn call(self: *Info, function: usize, args: anytype, term_hook: ?TermHook) noreturn {
+    pub fn call(self: *Info, function: usize, args: anytype, cleanup_hook: ?CleanupHook, term_hook: ?TermHook) noreturn {
         const Container = struct {
             fn terminate() linksection(".rethooks") callconv(.Naked) noreturn {
                 // Syscall #100011 is "terminate".
@@ -147,6 +155,7 @@ pub const Info = struct {
         };
 
         self.pc = function;
+        self.cleanup_hook = cleanup_hook;
         self.term_hook = term_hook;
         self.trap_frame.general_purpose_registers[1] = @intFromPtr(&Container.terminate);
         inline for (args, 0..) |arg, i| {
@@ -184,6 +193,9 @@ pub const Info = struct {
             self.rds.deinit();
         }
 
+        if (self.cleanup_hook) |cleanup_hook| {
+            cleanup_hook.cleanupFn(self, cleanup_hook.buffer, cleanup_hook.copy);
+        }
         if (self.term_hook) |term_hook| {
             term_hook.hookFn(term_hook.context, self);
         }
@@ -196,6 +208,48 @@ pub const Info = struct {
     fn shouldRemoveThread(self: *const Info, candidate: *const Info) bool {
         return candidate.thread_id == self.thread_id or self.thread_id == 0;
     }
+
+    pub fn copyBytes(self: *const Info, bytes: []const u8) ![]align(paging.page_size) const u8 {
+        const aligned_len = std.mem.alignForward(usize, bytes.len, paging.page_size);
+        const num_pages = @divExact(aligned_len, paging.page_size);
+
+        const copy = try paging.zeroedAlloc(num_pages);
+        errdefer paging.free(copy);
+
+        var addr = @intFromPtr(copy.ptr);
+        const limit = addr + copy.len;
+        while (addr < limit) : (addr += paging.page_size) {
+            try self.page_table.map(addr, addr, paging.EntryFlags.userReadOnly, 0);
+            errdefer self.page_table.unmapEntry(addr);
+        }
+
+        paging.setUserMemoryAccess(true);
+        defer paging.setUserMemoryAccess(false);
+
+        @memcpy(copy[0..bytes.len], bytes);
+        return copy[0..bytes.len];
+    }
+
+    pub fn copyBuffer(self: *const Info, buffer: []u8) ![]align(paging.page_size) u8 {
+        const aligned_len = std.mem.alignForward(usize, buffer.len, paging.page_size);
+        const num_pages = @divExact(aligned_len, paging.page_size);
+
+        const copy = try paging.zeroedAlloc(num_pages);
+        errdefer paging.free(copy);
+
+        var addr = @intFromPtr(copy.ptr);
+        const limit = addr + copy.len;
+        while (addr < limit) : (addr += paging.page_size) {
+            try self.page_table.map(addr, addr, paging.EntryFlags.userReadWrite, 0);
+            errdefer self.page_table.unmapEntry(addr);
+        }
+
+        paging.setUserMemoryAccess(true);
+        defer paging.setUserMemoryAccess(false);
+
+        @memcpy(copy[0..buffer.len], buffer);
+        return copy[0..buffer.len];
+    }
 };
 
 pub fn next() ?*Info {
@@ -344,6 +398,7 @@ pub fn create(allocator: std.mem.Allocator, elf_buf: []align(@alignOf(elf.Elf64_
         .pages = pages,
         .stack = @ptrCast(stack),
         .pc = hdr.entry,
+        .cleanup_hook = null,
         .term_hook = null,
         .page_table = procmem,
         .state = .waiting,