gcc-plugins: Remove ARM_SSP_PER_TASK plugin

As part of trying to remove GCC plugins from Linux, drop the
ARM_SSP_PER_TASK plugin. The feature is available upstream since GCC
12, so anyone needing newer kernels with per-task ssp can update their
compiler[1].

Suggested-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]/ [1]
Acked-by: Arnd Bergmann <[e-mail]>
Acked-by: Ard Biesheuvel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Kees Cook <[e-mail]>

arch/arm/Kconfig

···
 config STACKPROTECTOR_PER_TASK
 	bool "Use a unique stack canary value for each task"
 	depends on STACKPROTECTOR && CURRENT_POINTER_IN_TPIDRURO && !XIP_DEFLATED_DATA
-	depends on GCC_PLUGINS || CC_HAVE_STACKPROTECTOR_TLS
-	select GCC_PLUGIN_ARM_SSP_PER_TASK if !CC_HAVE_STACKPROTECTOR_TLS
+	depends on CC_HAVE_STACKPROTECTOR_TLS
 	default y
 	help
 	  Due to the fact that GCC uses an ordinary symbol reference from

arch/arm/boot/compressed/Makefile

···
 
 ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin \
 	     -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \
-	     -I$(obj) $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)
+	     -I$(obj)
 ccflags-remove-$(CONFIG_FUNCTION_TRACER) += -pg
 asflags-y := -DZIMAGE
 

scripts/Makefile.gcc-plugins

···
 endif
 export DISABLE_STACKLEAK_PLUGIN
 
-gcc-plugin-$(CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK) += arm_ssp_per_task_plugin.so
-ifdef CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK
-    DISABLE_ARM_SSP_PER_TASK_PLUGIN += -fplugin-arg-arm_ssp_per_task_plugin-disable
-endif
-export DISABLE_ARM_SSP_PER_TASK_PLUGIN
-
 # All the plugin CFLAGS are collected here in case a build target needs to
 # filter them out of the KBUILD_CFLAGS.
 GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))

scripts/gcc-plugins/Kconfig

···
 	   * https://grsecurity.net/
 	   * https://pax.grsecurity.net/
 
-config GCC_PLUGIN_ARM_SSP_PER_TASK
-	bool
-	depends on GCC_PLUGINS && ARM
-
 endif

scripts/gcc-plugins/arm_ssp_per_task_plugin.c

···
-// SPDX-License-Identifier: GPL-2.0
-
-#include "gcc-common.h"
-
-__visible int plugin_is_GPL_compatible;
-
-static unsigned int canary_offset;
-
-static unsigned int arm_pertask_ssp_rtl_execute(void)
-{
-	rtx_insn *insn;
-
-	for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) {
-		const char *sym;
-		rtx body;
-		rtx current;
-
-		/*
-		 * Find a SET insn involving a SYMBOL_REF to __stack_chk_guard
-		 */
-		if (!INSN_P(insn))
-			continue;
-		body = PATTERN(insn);
-		if (GET_CODE(body) != SET ||
-		    GET_CODE(SET_SRC(body)) != SYMBOL_REF)
-			continue;
-		sym = XSTR(SET_SRC(body), 0);
-		if (strcmp(sym, "__stack_chk_guard"))
-			continue;
-
-		/*
-		 * Replace the source of the SET insn with an expression that
-		 * produces the address of the current task's stack canary value
-		 */
-		current = gen_reg_rtx(Pmode);
-
-		emit_insn_before(gen_load_tp_hard(current), insn);
-
-		SET_SRC(body) = gen_rtx_PLUS(Pmode, current,
-					     GEN_INT(canary_offset));
-	}
-	return 0;
-}
-
-#define PASS_NAME arm_pertask_ssp_rtl
-
-#define NO_GATE
-#include "gcc-generate-rtl-pass.h"
-
-#if BUILDING_GCC_VERSION >= 9000
-static bool no(void)
-{
-	return false;
-}
-
-static void arm_pertask_ssp_start_unit(void *gcc_data, void *user_data)
-{
-	targetm.have_stack_protect_combined_set = no;
-	targetm.have_stack_protect_combined_test = no;
-}
-#endif
-
-__visible int plugin_init(struct plugin_name_args *plugin_info,
-			  struct plugin_gcc_version *version)
-{
-	const char * const plugin_name = plugin_info->base_name;
-	const int argc = plugin_info->argc;
-	const struct plugin_argument *argv = plugin_info->argv;
-	int i;
-
-	if (!plugin_default_version_check(version, &gcc_version)) {
-		error(G_("incompatible gcc/plugin versions"));
-		return 1;
-	}
-
-	for (i = 0; i < argc; ++i) {
-		if (!strcmp(argv[i].key, "disable"))
-			return 0;
-
-		/* all remaining options require a value */
-		if (!argv[i].value) {
-			error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
-			      plugin_name, argv[i].key);
-			return 1;
-		}
-
-		if (!strcmp(argv[i].key, "offset")) {
-			canary_offset = atoi(argv[i].value);
-			continue;
-		}
-		error(G_("unknown option '-fplugin-arg-%s-%s'"),
-		      plugin_name, argv[i].key);
-		return 1;
-	}
-
-	PASS_INFO(arm_pertask_ssp_rtl, "expand", 1, PASS_POS_INSERT_AFTER);
-
-	register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP,
-			  NULL, &arm_pertask_ssp_rtl_pass_info);
-
-#if BUILDING_GCC_VERSION >= 9000
-	register_callback(plugin_info->base_name, PLUGIN_START_UNIT,
-			  arm_pertask_ssp_start_unit, NULL);
-#endif
-
-	return 0;
-}