Add support for GPG signature enforcement on booted

kernels and related blobs

This can be used to implement a form of organization-controlled secure boot,
whereby kernels may be loaded from a variety of sources but they will only
boot if a valid signature file is found for each component, and only if the
signature is listed in the /etc/pb-lockdown file.

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
(Minor build fixes and gpgme.m4, comment on secure boot in gpg.c)

10 files changed, 208 insertions, 26 deletions

diff --git a/discover/Makefile.am b/discover/Makefile.am
index 899c9a6..4a6cbd0 100644
--- a/discover/Makefile.am
+++ b/discover/Makefile.am
@@ -58,7 +58,8 @@ discover_pb_discover_LDADD = \
 	discover/grub2/grub2-parser.ro \
 	discover/platform.ro \
 	$(core_lib) \
-	$(UDEV_LIBS)
+	$(UDEV_LIBS) \
+	$(GPGME_LIBS)
 
 discover_pb_discover_LDFLAGS = \
 	$(AM_LDFLAGS) \
diff --git a/discover/boot.c b/discover/boot.c
index 04e7a54..c4ddfef 100644
--- a/discover/boot.c
+++ b/discover/boot.c
@@ -26,27 +26,14 @@
 #include "resource.h"
 #include "platform.h"
 
+#include <security/gpg.h>
+
 static const char *boot_hook_dir = PKG_SYSCONF_DIR "/boot.d";
 enum {
 	BOOT_HOOK_EXIT_OK	= 0,
 	BOOT_HOOK_EXIT_UPDATE	= 2,
 };
 
-struct boot_task {
-	struct load_url_result *image;
-	struct load_url_result *initrd;
-	struct load_url_result *dtb;
-	const char *local_image;
-	const char *local_initrd;
-	const char *local_dtb;
-	const char *args;
-	const char *boot_tty;
-	boot_status_fn status_fn;
-	void *status_arg;
-	bool dry_run;
-	bool cancelled;
-};
-
 /**
  * kexec_load - kexec load helper.
  */
@@ -59,20 +46,39 @@ static int kexec_load(struct boot_task *boot_task)
 	char *s_dtb = NULL;
 	char *s_args = NULL;
 
+	boot_task->local_initrd_override = NULL;
+	boot_task->local_dtb_override = NULL;
+	boot_task->local_image_override = NULL;
+
+	if ((result = gpg_validate_boot_files(boot_task))) {
+		if (result == KEXEC_LOAD_SIGNATURE_FAILURE) {
+			pb_log("%s: Aborting kexec due to"
+				" signature verification failure\n", __func__);
+			goto abort_kexec;
+		}
+	}
+
+	const char* local_initrd = (boot_task->local_initrd_override) ?
+		boot_task->local_initrd_override : boot_task->local_initrd;
+	const char* local_dtb = (boot_task->local_dtb_override) ?
+		boot_task->local_dtb_override : boot_task->local_dtb;
+	const char* local_image = (boot_task->local_image_override) ?
+		boot_task->local_image_override : boot_task->local_image;
+
 	p = argv;
 	*p++ = pb_system_apps.kexec;	/* 1 */
 	*p++ = "-l";			/* 2 */
 
-	if (boot_task->local_initrd) {
+	if (local_initrd) {
 		s_initrd = talloc_asprintf(boot_task, "--initrd=%s",
-				boot_task->local_initrd);
+				local_initrd);
 		assert(s_initrd);
 		*p++ = s_initrd;	 /* 3 */
 	}
 
-	if (boot_task->local_dtb) {
+	if (local_dtb) {
 		s_dtb = talloc_asprintf(boot_task, "--dtb=%s",
-						boot_task->local_dtb);
+						local_dtb);
 		assert(s_dtb);
 		*p++ = s_dtb;		 /* 4 */
 	}
@@ -82,7 +88,7 @@ static int kexec_load(struct boot_task *boot_task)
 	assert(s_args);
 	*p++ = s_args;		/* 5 */
 
-	*p++ = boot_task->local_image;	/* 6 */
+	*p++ = local_image;		/* 6 */
 	*p++ = NULL;			/* 7 */
 
 	result = process_run_simple_argv(boot_task, argv);
@@ -90,6 +96,9 @@ static int kexec_load(struct boot_task *boot_task)
 	if (result)
 		pb_log("%s: failed: (%d)\n", __func__, result);
 
+abort_kexec:
+	gpg_validate_boot_files_cleanup(boot_task);
+
 	return result;
 }
 
@@ -376,23 +385,69 @@ static void boot_process(struct load_url_result *result, void *data)
 			check_load(task, "dtb", task->dtb))
 		goto no_load;
 
+	if (task->verify_signature) {
+		if (load_pending(task->image_signature) ||
+				load_pending(task->initrd_signature) ||
+				load_pending(task->dtb_signature) ||
+				load_pending(task->cmdline_signature))
+			return;
+
+		if (check_load(task, "kernel image signature",
+					task->image_signature) ||
+				check_load(task, "initrd signature",
+					task->initrd_signature) ||
+				check_load(task, "dtb signature",
+					task->dtb_signature) ||
+				check_load(task, "command line signature",
+					task->cmdline_signature))
+			goto no_sig_load;
+	}
+
 	/* we make a copy of the local paths, as the boot hooks might update
 	 * and/or create these */
 	task->local_image = task->image ? task->image->local : NULL;
 	task->local_initrd = task->initrd ? task->initrd->local : NULL;
 	task->local_dtb = task->dtb ? task->dtb->local : NULL;
 
+	if (task->verify_signature) {
+		task->local_image_signature = task->image_signature ?
+			task->image_signature->local : NULL;
+		task->local_initrd_signature = task->initrd_signature ?
+			task->initrd_signature->local : NULL;
+		task->local_dtb_signature = task->dtb_signature ?
+			task->dtb_signature->local : NULL;
+		task->local_cmdline_signature = task->cmdline_signature ?
+			task->cmdline_signature->local : NULL;
+	}
+
 	run_boot_hooks(task);
 
 	update_status(task->status_fn, task->status_arg, BOOT_STATUS_INFO,
 			_("performing kexec_load"));
 
 	rc = kexec_load(task);
-	if (rc) {
+	if (rc == KEXEC_LOAD_SIGNATURE_FAILURE) {
+		update_status(task->status_fn, task->status_arg,
+				BOOT_STATUS_ERROR,
+				_("signature verification failed"));
+	}
+	else if (rc == KEXEC_LOAD_SIG_SETUP_INVALID) {
+		update_status(task->status_fn, task->status_arg,
+				BOOT_STATUS_ERROR,
+				_("invalid signature configuration"));
+	}
+	else if (rc) {
 		update_status(task->status_fn, task->status_arg,
-				BOOT_STATUS_ERROR, _("kexec load failed"));
+				BOOT_STATUS_ERROR,
+				_("kexec load failed"));
 	}
 
+no_sig_load:
+	cleanup_load(task->image_signature);
+	cleanup_load(task->initrd_signature);
+	cleanup_load(task->dtb_signature);
+	cleanup_load(task->cmdline_signature);
+
 no_load:
 	cleanup_load(task->image);
 	cleanup_load(task->initrd);
@@ -433,6 +488,8 @@ struct boot_task *boot(void *ctx, struct discover_boot_option *opt,
 		boot_status_fn status_fn, void *status_arg)
 {
 	struct pb_url *image = NULL, *initrd = NULL, *dtb = NULL;
+	struct pb_url *image_sig = NULL, *initrd_sig = NULL, *dtb_sig = NULL,
+		*cmdline_sig = NULL;
 	const struct config *config;
 	struct boot_task *boot_task;
 	const char *boot_desc;
@@ -476,6 +533,8 @@ struct boot_task *boot(void *ctx, struct discover_boot_option *opt,
 	boot_task->status_fn = status_fn;
 	boot_task->status_arg = status_arg;
 
+	boot_task->verify_signature = (lockdown_status() == PB_LOCKDOWN_SIGN);
+
 	if (cmd && cmd->boot_args) {
 		boot_task->args = talloc_strdup(boot_task, cmd->boot_args);
 	} else if (opt && opt->option->boot_args) {
@@ -492,11 +551,52 @@ struct boot_task *boot(void *ctx, struct discover_boot_option *opt,
 		boot_task->boot_tty = config ? config->boot_tty : NULL;
 	}
 
+	if (boot_task->verify_signature) {
+		if (cmd && cmd->args_sig_file) {
+			cmdline_sig = pb_url_parse(opt, cmd->args_sig_file);
+		} else if (opt && opt->args_sig_file) {
+			cmdline_sig = opt->args_sig_file->url;
+		} else {
+			pb_log("%s: no command line signature file"
+				" specified\n", __func__);
+			update_status(status_fn, status_arg, BOOT_STATUS_INFO,
+					_("Boot failed: no command line"
+						" signature file specified"));
+			talloc_free(boot_task);
+			return NULL;
+		}
+	}
+
 	/* start async loads for boot resources */
 	rc = start_url_load(boot_task, "kernel image", image, &boot_task->image)
 	  || start_url_load(boot_task, "initrd", initrd, &boot_task->initrd)
 	  || start_url_load(boot_task, "dtb", dtb, &boot_task->dtb);
 
+	if (boot_task->verify_signature) {
+		/* Generate names of associated signature files and load */
+		if (image) {
+			image_sig = gpg_get_signature_url(ctx, image);
+			rc |= start_url_load(boot_task,
+				"kernel image signature", image_sig,
+				&boot_task->image_signature);
+		}
+		if (initrd) {
+			initrd_sig = gpg_get_signature_url(ctx, initrd);
+			rc |= start_url_load(boot_task, "initrd signature",
+				initrd_sig, &boot_task->initrd_signature);
+		}
+		if (dtb) {
+			dtb_sig = gpg_get_signature_url(ctx, dtb);
+			rc |= start_url_load(boot_task, "dtb signature",
+				dtb_sig, &boot_task->dtb_signature);
+		}
+
+		rc |= start_url_load(boot_task,
+			"kernel command line signature", cmdline_sig,
+			&boot_task->cmdline_signature);
+	}
+
+	/* If all URLs are local, we may be done. */
 	if (rc) {
 		/* Don't call boot_cancel() to preserve the status update */
 		boot_task->cancelled = true;
diff --git a/discover/boot.h b/discover/boot.h
index ec61703..2190495 100644
--- a/discover/boot.h
+++ b/discover/boot.h
@@ -1,6 +1,9 @@
 #ifndef _BOOT_H
 #define _BOOT_H
 
+#include <types/types.h>
+#include "device-handler.h"
+
 struct boot_option;
 struct boot_command;
 
@@ -11,4 +14,37 @@ struct boot_task *boot(void *ctx, struct discover_boot_option *opt,
 		boot_status_fn status_fn, void *status_arg);
 
 void boot_cancel(struct boot_task *task);
+
+struct boot_task {
+	struct load_url_result *image;
+	struct load_url_result *initrd;
+	struct load_url_result *dtb;
+	const char *local_image;
+	const char *local_initrd;
+	const char *local_dtb;
+	char *local_image_override;
+	char *local_initrd_override;
+	char *local_dtb_override;
+	const char *args;
+	const char *boot_tty;
+	boot_status_fn status_fn;
+	void *status_arg;
+	bool dry_run;
+	bool cancelled;
+	bool verify_signature;
+	struct load_url_result *image_signature;
+	struct load_url_result *initrd_signature;
+	struct load_url_result *dtb_signature;
+	struct load_url_result *cmdline_signature;
+	const char *local_image_signature;
+	const char *local_initrd_signature;
+	const char *local_dtb_signature;
+	const char *local_cmdline_signature;
+};
+
+enum {
+	KEXEC_LOAD_SIG_SETUP_INVALID = 253,
+	KEXEC_LOAD_SIGNATURE_FAILURE = 254,
+};
+
 #endif /* _BOOT_H */
diff --git a/discover/device-handler.c b/discover/device-handler.c
index c31fcea..f6b6d22 100644
--- a/discover/device-handler.c
+++ b/discover/device-handler.c
@@ -613,6 +613,7 @@ static bool __attribute__((used)) boot_option_is_resolved(
 	return resource_is_resolved(opt->boot_image) &&
 		resource_is_resolved(opt->initrd) &&
 		resource_is_resolved(opt->dtb) &&
+		resource_is_resolved(opt->args_sig_file) &&
 		resource_is_resolved(opt->icon);
 }
 
@@ -638,6 +639,8 @@ static bool boot_option_resolve(struct discover_boot_option *opt,
 	return resource_resolve(opt->boot_image, "boot_image", opt, handler) &&
 		resource_resolve(opt->initrd, "initrd", opt, handler) &&
 		resource_resolve(opt->dtb, "dtb", opt, handler) &&
+		resource_resolve(opt->args_sig_file, "args_sig_file", opt,
+			handler) &&
 		resource_resolve(opt->icon, "icon", opt, handler);
 }
 
@@ -652,6 +655,7 @@ static void boot_option_finalise(struct device_handler *handler,
 	assert(!opt->option->dtb_file);
 	assert(!opt->option->icon_file);
 	assert(!opt->option->device_id);
+	assert(!opt->option->args_sig_file);
 
 	if (opt->boot_image)
 		opt->option->boot_image_file = opt->boot_image->url->full;
@@ -661,6 +665,8 @@ static void boot_option_finalise(struct device_handler *handler,
 		opt->option->dtb_file = opt->dtb->url->full;
 	if (opt->icon)
 		opt->option->icon_file = opt->icon->url->full;
+	if (opt->args_sig_file)
+		opt->option->args_sig_file = opt->args_sig_file->url->full;
 
 	opt->option->device_id = opt->device->device->id;
 
diff --git a/discover/device-handler.h b/discover/device-handler.h
index b6f9fd5..f785ccc 100644
--- a/discover/device-handler.h
+++ b/discover/device-handler.h
@@ -48,6 +48,7 @@ struct discover_boot_option {
 	struct resource		*boot_image;
 	struct resource		*initrd;
 	struct resource		*dtb;
+	struct resource		*args_sig_file;
 	struct resource		*icon;
 };
 
diff --git a/discover/grub2/builtins.c b/discover/grub2/builtins.c
index 8bff732..c16b639 100644
--- a/discover/grub2/builtins.c
+++ b/discover/grub2/builtins.c
@@ -6,7 +6,9 @@
 #include <types/types.h>
 #include <talloc/talloc.h>
 #include <util/util.h>
+#include <url/url.h>
 
+#include "discover/resource.h"
 #include "discover/parser.h"
 #include "grub2.h"
 
@@ -69,6 +71,12 @@ static int builtin_linux(struct grub2_script *script,
 		opt->option->boot_args = talloc_asprintf_append(
 						opt->option->boot_args,
 						" %s", argv[i]);
+
+	char* args_sigfile_default = talloc_asprintf(opt,
+		"%s.cmdline.sig", argv[1]);
+	opt->args_sig_file = create_grub2_resource(opt, script->ctx->device,
+						root, args_sigfile_default);
+	talloc_free(args_sigfile_default);
 	return 0;
 }
 
diff --git a/discover/kboot-parser.c b/discover/kboot-parser.c
index cebe787..f7f75e0 100644
--- a/discover/kboot-parser.c
+++ b/discover/kboot-parser.c
@@ -96,6 +96,12 @@ out_add:
 	d_opt->boot_image = create_devpath_resource(d_opt,
 				conf->dc->device, value);
 
+	char* args_sigfile_default = talloc_asprintf(d_opt,
+		"%s.cmdline.sig", value);
+	d_opt->args_sig_file = create_devpath_resource(d_opt,
+				conf->dc->device, args_sigfile_default);
+	talloc_free(args_sigfile_default);
+
 	if (root) {
 		opt->boot_args = talloc_asprintf(opt, "root=%s %s", root, args);
 		talloc_free(args);
diff --git a/discover/pxe-parser.c b/discover/pxe-parser.c
index 4481e5d..4aae8b1 100644
--- a/discover/pxe-parser.c
+++ b/discover/pxe-parser.c
@@ -166,6 +166,13 @@ static void pxe_process_pair(struct conf_context *ctx,
 		url = pxe_url_join(ctx->dc, ctx->dc->conf_url, value);
 		opt->boot_image = create_url_resource(opt, url);
 
+		char* args_sigfile_default = talloc_asprintf(opt,
+			"%s.cmdline.sig", value);
+		url = pxe_url_join(ctx->dc, ctx->dc->conf_url,
+			args_sigfile_default);
+		opt->args_sig_file = create_url_resource(opt, url);
+		talloc_free(args_sigfile_default);
+
 	} else if (streq(name, "INITRD")) {
 		url = pxe_url_join(ctx->dc, ctx->dc->conf_url, value);
 		opt->initrd = create_url_resource(opt, url);
diff --git a/discover/user-event.c b/discover/user-event.c
index 7350b6c..6ea754f 100644
--- a/discover/user-event.c
+++ b/discover/user-event.c
@@ -82,7 +82,7 @@ static void user_event_print_event(struct event __attribute__((unused)) *event)
 }
 
 static struct resource *user_event_resource(struct discover_boot_option *opt,
-		struct event *event)
+		struct event *event, bool gen_boot_args_sigfile)
 {
 	const char *siaddr, *boot_file;
 	struct resource *res;
@@ -101,7 +101,16 @@ static struct resource *user_event_resource(struct discover_boot_option *opt,
 		return NULL;
 	}
 
-	url_str = talloc_asprintf(opt, "%s%s/%s", "tftp://", siaddr, boot_file);
+	if (gen_boot_args_sigfile) {
+		char* args_sigfile_default = talloc_asprintf(opt,
+			"%s.cmdline.sig", boot_file);
+		url_str = talloc_asprintf(opt, "%s%s/%s", "tftp://", siaddr,
+			args_sigfile_default);
+		talloc_free(args_sigfile_default);
+	}
+	else
+		url_str = talloc_asprintf(opt, "%s%s/%s", "tftp://", siaddr,
+			boot_file);
 	url = pb_url_parse(opt, url_str);
 	talloc_free(url_str);
 
@@ -143,12 +152,13 @@ static int parse_user_event(struct discover_context *ctx, struct event *event)
 	opt->id = talloc_asprintf(opt, "%s#%s", dev->id, val);
 	opt->name = talloc_strdup(opt, val);
 
-	d_opt->boot_image = user_event_resource(d_opt, event);
+	d_opt->boot_image = user_event_resource(d_opt, event, false);
 	if (!d_opt->boot_image) {
 		pb_log("%s: no boot image found for %s!\n", __func__,
 				opt->name);
 		goto fail_opt;
 	}
+	d_opt->args_sig_file = user_event_resource(d_opt, event, true);
 
 	val = event_get_param(event, "rootpath");
 	if (val) {
diff --git a/discover/yaboot-parser.c b/discover/yaboot-parser.c
index aa99392..b62f39d 100644
--- a/discover/yaboot-parser.c
+++ b/discover/yaboot-parser.c
@@ -114,6 +114,13 @@ static void yaboot_finish(struct conf_context *conf)
 	/* populate the boot option from state data */
 	state->opt->boot_image = create_yaboot_devpath_resource(state,
 				conf, state->boot_image);
+
+	char* args_sigfile_default = talloc_asprintf(opt,
+		"%s.cmdline.sig", state->boot_image);
+	state->opt->args_sig_file = create_yaboot_devpath_resource(state,
+				conf, args_sigfile_default);
+	talloc_free(args_sigfile_default);
+
 	if (state->initrd) {
 		state->opt->initrd = create_yaboot_devpath_resource(state,
 				conf, state->initrd);