frida-helper-backend: add option to allocate stack

For some target programs it's not reasonable to assume that any hijacked
thread has a large stack. For example, in Go, stacks are often small and
are allocated on the heap. The injector bootstrap program uses kilobytes
of stack. In order to side-step this problem, this patch enables an
option to allocate an auxiliary stack for the remote call to use and,
for the bootstrapper and loader, uses it.

The calls to mmap and munmap don't use much stack, so they are fine.

Fixes #544

meson.build

@@ -668,6 +668,12 @@ if have_mapper
   cdata.set('HAVE_MAPPER', 1)
 endif
 
+
+allocate_linux_injector_stack_opt = get_option('allocate-linux-injector-stack')
+if allocate_linux_injector_stack_opt.enabled()
+  vala_flags += ['--define=ALLOCATE_LINUX_INJECTOR_STACK']
+endif
+
 configure_file(
   output: 'config.h',
   configuration: cdata)

meson.options

@@ -161,3 +161,9 @@ option('tests',
   value: 'auto',
   description: 'Build tests'
 )
+
+option('allocate-linux-injector-stack',
+  type: 'feature',
+  value: 'disabled',
+  description: 'Allocate a new stack for injected remote calls in linux'
+)

src/linux/frida-helper-backend.vala

@@ -1018,7 +1018,11 @@ namespace Frida {
 
 			uint64 loader_base = (uintptr) bres.context.allocation_base;
 
-			var call_builder = new RemoteCallBuilder (loader_base, saved_regs);
+			GPRegs regs = saved_regs;
+#if ALLOCATE_LINUX_INJECTOR_STACK
+			regs.stack_pointer = bres.allocated_stack.stack_root;
+#endif
+			var call_builder = new RemoteCallBuilder (loader_base, regs);
 			call_builder.add_argument (loader_base + loader_layout.ctx_offset);
 			RemoteCall loader_call = call_builder.build (this);
 			RemoteCallResult loader_result = yield loader_call.execute (cancellable);
@@ -1078,7 +1082,10 @@ namespace Frida {
 
 			uint64 allocation_base = 0;
 			size_t allocation_size = size_t.max (bootstrapper_size, loader_size);
-
+#if ALLOCATE_LINUX_INJECTOR_STACK
+			uint64 stack_base = 0;
+			size_t stack_size = 64 << 10; // enough for the bootstrapper
+#endif
 			uint64 remote_mmap = 0;
 			uint64 remote_munmap = 0;
 			ProcMapsEntry? remote_libc = ProcMapsEntry.find_by_path (pid, local_libc.path);
@@ -1121,6 +1128,16 @@ namespace Frida {
 				code_swap.revert ();
 			}
 
+#if ALLOCATE_LINUX_INJECTOR_STACK
+			stack_base = yield allocate_memory (remote_mmap, stack_size,
+					Posix.PROT_READ | Posix.PROT_WRITE | Posix.PROT_EXEC, cancellable);
+			result.allocated_stack.stack_base = (void *)stack_base;
+			result.allocated_stack.stack_size = stack_size;
+			GPRegs regs = saved_regs;
+			regs.stack_pointer = result.allocated_stack.stack_root;
+#else
+			GPRegs regs = saved_regs;
+#endif
 			try {
 				write_memory (allocation_base, bootstrapper_code);
 				maybe_fixup_helper_code (allocation_base, bootstrapper_code);
@@ -1129,7 +1146,7 @@ namespace Frida {
 
 				HelperBootstrapStatus status = SUCCESS;
 				do {
-					var call_builder = new RemoteCallBuilder (code_start, saved_regs);
+					var call_builder = new RemoteCallBuilder (code_start, regs);
 
 					unowned uint8[] fallback_ld_data = fallback_ld.data;
 					unowned uint8[] fallback_libc_data = fallback_libc.data;
@@ -1198,6 +1215,12 @@ namespace Frida {
 						yield deallocate_memory (remote_munmap, allocation_base, allocation_size, null);
 					} catch (GLib.Error e) {
 					}
+#if ALLOCATE_LINUX_INJECTOR_STACK
+					try {
+						yield deallocate_memory (remote_munmap, stack_base, stack_size, null);
+					} catch (GLib.Error e) {
+					}
+#endif
 				}
 
 				throw_api_error (e);
@@ -1393,8 +1416,15 @@ namespace Frida {
 		}
 
 		public async void deallocate (BootstrapResult bres, Cancellable? cancellable) throws Error, IOError {
+
 			yield deallocate_memory ((uintptr) bres.libc.munmap, (uintptr) bres.context.allocation_base,
 				bres.context.allocation_size, cancellable);
+#if ALLOCATE_LINUX_INJECTOR_STACK
+			if (bres.allocated_stack.stack_base != null) {
+				yield deallocate_memory ((uintptr) bres.libc.munmap, (uintptr) bres.allocated_stack.stack_base,
+					(size_t) bres.allocated_stack.stack_size, cancellable);
+			}
+#endif	
 		}
 	}
 
@@ -1416,14 +1446,34 @@ namespace Frida {
 		}
 	}
 
+#if ALLOCATE_LINUX_INJECTOR_STACK
+	private struct AllocatedStack {
+		public void * stack_base;
+		public uint64 stack_size;
+
+		public uint64 stack_root {
+			get {
+				return ((uint64) stack_base) + stack_size;
+			}
+		}
+	}
+#endif
+
+
 	private class BootstrapResult {
 		public HelperBootstrapContext context;
 		public HelperLibcApi libc;
+#if ALLOCATE_LINUX_INJECTOR_STACK
+		public AllocatedStack allocated_stack;
+#endif
 
 		public BootstrapResult clone () {
 			var res = new BootstrapResult ();
 			res.context = context;
 			res.libc = libc;
+#if ALLOCATE_LINUX_INJECTOR_STACK
+			res.allocated_stack = allocated_stack;
+#endif
 			return res;
 		}
 	}