New gcc-plugin:

- Enable per-task stack protector for ARM (Ard Biesheuvel)
 -----BEGIN PGP SIGNATURE-----
 Comment: Kees Cook <kees@outflux.net>
 
 iQJKBAABCgA0FiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAlwYN04WHGtlZXNjb29r
 QGNocm9taXVtLm9yZwAKCRCJcvTf3G3AJhUkD/4i0FW2fW1tY63lnbKhp6LFSGvF
 N7OdwPXwS5dlmVY8KFFrJp0GlT8qvJ3Kqwit5QTu9U9Mo32UbAVwB6gEW/kT3oB3
 Pk9pR/DMhTTxD6mUjIHq2c/IJgzw42slTbf1ezb5RtmFYaxqbX1A/wKes7ZTtp23
 JtNw2EkqDGMeMNDCbIZAaPHC7fwk6t40qgyrLOAHz+jnrL9tEd9/UIdqaRTn6HKE
 nslegmaDAUmPmmG8UK3RITQBD+FZsizcz/n2xKkCB79fld0qGwlUriacSmwVScBS
 LzGvVSrjUbfo/oo850RgrE48GxxlQntOF0z1foRQ7EFygk4gPPsqYRE9OvjE2Iid
 9BNtImt6mvOw7faD7sS6R9U5n/66Q3qlHi5FcU8ID6wVjwPM0RX0G4SDO/aTL//w
 FedMx4PPQtzQIH+X0WxI3mXreuEmN36rnQBR6XovBg2IBlmT6zMRXKhC+50U8+89
 WCUeWCuUz4p4daPgV4xKJu8H7EJxQN3YQ2IMStJCAgmrMAUX710pkJ5bt7meGg6Y
 LUPxRVBeQIC9UuJBDWzMbCYpHx/09o8FsFSEd/M6hW9NhGKo6PIGUu+1oy12LuqM
 eqb+m4wnylUXeaZnDTIYaVzwfCDCcMPTnt2X3Czc1huq8A5pGmfbUGBLMKHVoguA
 8J3bD55suTMTZut3vA==
 =AkLm
 -----END PGP SIGNATURE-----

Merge tag 'gcc-plugins-v4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull gcc-plugins update from Kees Cook:
 "Both arm and arm64 are gaining per-task stack canaries (to match x86),
  but arm is being done with a gcc plugin, hence it going through the
  gcc-plugins tree.

  New gcc-plugin:

   - Enable per-task stack protector for ARM (Ard Biesheuvel)"

* tag 'gcc-plugins-v4.21-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  ARM: smp: add support for per-task stack canaries

scripts/gcc-plugins/Kconfig

@@ -190,4 +190,8 @@ config STACKLEAK_RUNTIME_DISABLE
 	  runtime to control kernel stack erasing for kernels built with
 	  CONFIG_GCC_PLUGIN_STACKLEAK.
 
+config GCC_PLUGIN_ARM_SSP_PER_TASK
+	bool
+	depends on GCC_PLUGINS && ARM
+
 endif

scripts/gcc-plugins/arm_ssp_per_task_plugin.c

@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "gcc-common.h"
+
+__visible int plugin_is_GPL_compatible;
+
+static unsigned int sp_mask, 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 masked_sp;
+
+		/*
+		 * 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 copy of the stack canary value
+		 * stored in struct thread_info
+		 */
+		masked_sp = gen_reg_rtx(Pmode);
+
+		emit_insn_before(gen_rtx_SET(masked_sp,
+					     gen_rtx_AND(Pmode,
+							 stack_pointer_rtx,
+							 GEN_INT(sp_mask))),
+				 insn);
+
+		SET_SRC(body) = gen_rtx_PLUS(Pmode, masked_sp,
+					     GEN_INT(canary_offset));
+	}
+	return 0;
+}
+
+#define PASS_NAME arm_pertask_ssp_rtl
+
+#define NO_GATE
+#include "gcc-generate-rtl-pass.h"
+
+__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 tso = 0;
+	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, "tso")) {
+			tso = atoi(argv[i].value);
+			continue;
+		}
+
+		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;
+	}
+
+	/* create the mask that produces the base of the stack */
+	sp_mask = ~((1U << (12 + tso)) - 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);
+
+	return 0;
+}