From nobody Wed Dec 17 17:59:30 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 002FCC3063E for ; Thu, 17 Aug 2023 15:13:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352919AbjHQPMd (ORCPT ); Thu, 17 Aug 2023 11:12:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352961AbjHQPML (ORCPT ); Thu, 17 Aug 2023 11:12:11 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D6C0F35A9; Thu, 17 Aug 2023 08:11:45 -0700 (PDT) Date: Thu, 17 Aug 2023 15:10:55 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1692285055; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=F4WpvSXJBp7tslXt/lRAPmiV67xkXdU4wz4n5XJbLWk=; b=Q1+j9/1ovZc/aOS1Njm1tormTZiZWUmZZXhH0mwERciU4WiT2SlgZwyAMvNH1uL2K9qVo0 Bv/gF05ru5aPMUAdJTWopnENe3Ng1fNf6zglp+Oeo5pR1Gmf47odL191o5GWQUkjafI6AL ai5Pkr1Lfw/n3JhyahPxOhFyt9NEDwZGT0c0tS4PH055s//k+TUT23wWY8SUrqOPJt6EVZ ud8hZUcazt538a+zLGUFuY7+Go24o8oZtHUpon4/bfMX/vqR3ZJgge9+0WzDkcw/OPkNDR OQvt3BM2z89p179jsldJ8m/DniIkJ8gWQAbEFcUXh6Ux2JRvvcKLhxThozNA/A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1692285055; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=F4WpvSXJBp7tslXt/lRAPmiV67xkXdU4wz4n5XJbLWk=; b=ACGc2uCV/WY6lAB/Zq2uiDJ7jJ3HFzOnpBCHlRt7ab/AOLhH7jCxXbkLZq/NxRWxdL5oxl 0Vv56fYBVTGavjCQ== From: "tip-bot2 for Josh Poimboeuf" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/shstk] x86/ibt: Convert IBT selftest to asm Cc: Josh Poimboeuf , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <99a7e16b97bda97bf0a04aa141d6241cd8a839a2.1680912949.git.jpoimboe@kernel.org> References: <99a7e16b97bda97bf0a04aa141d6241cd8a839a2.1680912949.git.jpoimboe@kernel.org> MIME-Version: 1.0 Message-ID: <169228505520.27769.12332470800067037980.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the x86/shstk branch of tip: Commit-ID: c6cfcbd8ca43766851a8c952e3b570727147020f Gitweb: https://git.kernel.org/tip/c6cfcbd8ca43766851a8c952e3b570727= 147020f Author: Josh Poimboeuf AuthorDate: Fri, 07 Apr 2023 17:16:41 -07:00 Committer: Peter Zijlstra CommitterDate: Thu, 17 Aug 2023 17:07:09 +02:00 x86/ibt: Convert IBT selftest to asm The following warning is reported when frame pointers and kernel IBT are enabled: vmlinux.o: warning: objtool: ibt_selftest+0x11: sibling call from callabl= e instruction with modified stack frame The problem is that objtool interprets the indirect branch in ibt_selftest() as a sibling call, and GCC inserts a (partial) frame pointer prologue before it: 0000 000000000003f550 : 0000 3f550: f3 0f 1e fa endbr64 0004 3f554: e8 00 00 00 00 call 3f559 3f55= 5: R_X86_64_PLT32 __fentry__-0x4 0009 3f559: 55 push %rbp 000a 3f55a: 48 8d 05 02 00 00 00 lea 0x2(%rip),%rax # 3f563= 0011 3f561: ff e0 jmp *%rax Note the inline asm is missing ASM_CALL_CONSTRAINT, so the 'push %rbp' happens before the indirect branch and the 'mov %rsp, %rbp' happens afterwards. Simplify the generated code and make it easier to understand for both tools and humans by moving the selftest to proper asm. Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/99a7e16b97bda97bf0a04aa141d6241cd8a839a2.16= 80912949.git.jpoimboe@kernel.org --- arch/x86/include/asm/traps.h | 3 ++- arch/x86/kernel/Makefile | 1 + arch/x86/kernel/cet.c | 23 +---------------------- arch/x86/kernel/cpu/common.c | 2 +- arch/x86/kernel/ibt_selftest.S | 17 +++++++++++++++++ 5 files changed, 22 insertions(+), 24 deletions(-) create mode 100644 arch/x86/kernel/ibt_selftest.S diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h index 75e0dab..b1c9cea 100644 --- a/arch/x86/include/asm/traps.h +++ b/arch/x86/include/asm/traps.h @@ -18,7 +18,8 @@ void __init trap_init(void); asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_r= egs *eregs); #endif =20 -extern bool ibt_selftest(void); +extern int ibt_selftest(void); +extern int ibt_selftest_noendbr(void); =20 #ifdef CONFIG_X86_F00F_BUG /* For handling the FOOF bug */ diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 6b6bf47..eca9784 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -49,6 +49,7 @@ obj-y +=3D process_$(BITS).o signal.o signal_$(BITS).o obj-y +=3D traps.o idt.o irq.o irq_$(BITS).o dumpstack_$(BITS).o obj-y +=3D time.o ioport.o dumpstack.o nmi.o obj-$(CONFIG_MODIFY_LDT_SYSCALL) +=3D ldt.o +obj-$(CONFIG_X86_KERNEL_IBT) +=3D ibt_selftest.o obj-y +=3D setup.o x86_init.o i8259.o irqinit.o obj-$(CONFIG_JUMP_LABEL) +=3D jump_label.o obj-$(CONFIG_IRQ_WORK) +=3D irq_work.o diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index cc10d8b..d2c732a 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -81,9 +81,6 @@ static void do_user_cp_fault(struct pt_regs *regs, unsign= ed long error_code) =20 static __ro_after_init bool ibt_fatal =3D true; =20 -/* code label defined in asm below */ -extern void ibt_selftest_ip(void); - static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_c= ode) { if ((error_code & CP_EC) !=3D CP_ENDBR) { @@ -91,7 +88,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsi= gned long error_code) return; } =20 - if (unlikely(regs->ip =3D=3D (unsigned long)&ibt_selftest_ip)) { + if (unlikely(regs->ip =3D=3D (unsigned long)&ibt_selftest_noendbr)) { regs->ax =3D 0; return; } @@ -105,24 +102,6 @@ static void do_kernel_cp_fault(struct pt_regs *regs, u= nsigned long error_code) BUG(); } =20 -/* Must be noinline to ensure uniqueness of ibt_selftest_ip. */ -noinline bool ibt_selftest(void) -{ - unsigned long ret; - - asm (" lea ibt_selftest_ip(%%rip), %%rax\n\t" - ANNOTATE_RETPOLINE_SAFE - " jmp *%%rax\n\t" - "ibt_selftest_ip:\n\t" - UNWIND_HINT_FUNC - ANNOTATE_NOENDBR - " nop\n\t" - - : "=3Da" (ret) : : "memory"); - - return !ret; -} - static int __init ibt_setup(char *str) { if (!strcmp(str, "off")) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index cf5275a..3c6426c 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -610,7 +610,7 @@ static __always_inline void setup_cet(struct cpuinfo_x8= 6 *c) =20 cr4_set_bits(X86_CR4_CET); =20 - if (kernel_ibt && !ibt_selftest()) { + if (kernel_ibt && ibt_selftest()) { pr_err("IBT selftest: Failed!\n"); wrmsrl(MSR_IA32_S_CET, 0); setup_clear_cpu_cap(X86_FEATURE_IBT); diff --git a/arch/x86/kernel/ibt_selftest.S b/arch/x86/kernel/ibt_selftest.S new file mode 100644 index 0000000..c43c4ed --- /dev/null +++ b/arch/x86/kernel/ibt_selftest.S @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#include +#include +#include + +SYM_CODE_START(ibt_selftest_noendbr) + ANNOTATE_NOENDBR + UNWIND_HINT_FUNC + /* #CP handler sets %ax to 0 */ + RET +SYM_CODE_END(ibt_selftest_noendbr) + +SYM_FUNC_START(ibt_selftest) + lea ibt_selftest_noendbr(%rip), %rax + ANNOTATE_RETPOLINE_SAFE + jmp *%rax +SYM_FUNC_END(ibt_selftest)