From nobody Wed Dec 17 07:27:49 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 D575DC4167B for ; Wed, 29 Nov 2023 13:34:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234492AbjK2NeQ (ORCPT ); Wed, 29 Nov 2023 08:34:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234329AbjK2NeD (ORCPT ); Wed, 29 Nov 2023 08:34:03 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2a07:de40:b251:101:10:150:64:2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3A0C11990 for ; Wed, 29 Nov 2023 05:34:09 -0800 (PST) Received: from imap2.dmz-prg2.suse.org (imap2.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:98]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id DADD21FCE8; Wed, 29 Nov 2023 13:34:07 +0000 (UTC) Received: from imap2.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap2.dmz-prg2.suse.org (Postfix) with ESMTPS id 9D5441376F; Wed, 29 Nov 2023 13:34:07 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap2.dmz-prg2.suse.org with ESMTPSA id oQk1Jc89Z2WVHwAAn2gu4w (envelope-from ); Wed, 29 Nov 2023 13:34:07 +0000 From: Juergen Gross To: linux-kernel@vger.kernel.org, x86@kernel.org Cc: Juergen Gross , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Peter Zijlstra Subject: [PATCH v5 3/5] x86/alternative: add indirect call patching Date: Wed, 29 Nov 2023 14:33:30 +0100 Message-Id: <20231129133332.31043-4-jgross@suse.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20231129133332.31043-1-jgross@suse.com> References: <20231129133332.31043-1-jgross@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Authentication-Results: smtp-out2.suse.de; none X-Rspamd-Server: rspamd2 X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[] X-Rspamd-Queue-Id: DADD21FCE8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" In order to prepare replacing of paravirt patching with alternative patching, add the capability to replace an indirect call with a direct one to alternative patching. This is done via a new flag ALT_FLAG_CALL as the target of the call instruction needs to be evaluated using the value of the location addressed by the indirect call. For convenience add a macro for a default call instruction. In case it is being used without the new flag being set, it will result in a BUG() when being executed. As in most cases the feature used will be X86_FEATURE_ALWAYS add another macro ALT_CALL_ALWAYS usable for the flags parameter of the ALTERNATIVE macros. For a complete replacement handle the special cases of calling a nop function and an indirect call of NULL the same way as paravirt does. Signed-off-by: Juergen Gross Signed-off-by: Peter Zijlstra (Intel) --- V4: - 32-bit mode doesn't have %rip relative addressing (kernel test robot) - define ALT_CALL_INSTR in assembly, too (kernel test robot) V5: - BUG() in case of inconsistent flag/instruction (Boris Petkov) - rename flag (Boris Petkov) - make target address calculation more readable (Boris Petkov) --- arch/x86/include/asm/alternative.h | 9 ++++++ arch/x86/kernel/alternative.c | 47 ++++++++++++++++++++++++++++++ 2 files changed, 56 insertions(+) diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alte= rnative.h index ce788ab4e77c..472334eed6f3 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -10,6 +10,9 @@ =20 #define ALT_FLAG_NOT (1 << 0) #define ALT_NOT(feature) ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature)) +#define ALT_FLAG_DIRECT_CALL (1 << 1) +#define ALT_DIRECT_CALL(feature) ((ALT_FLAG_DIRECT_CALL << ALT_FLAGS_SHIFT= ) | (feature)) +#define ALT_CALL_ALWAYS ALT_DIRECT_CALL(X86_FEATURE_ALWAYS) =20 #ifndef __ASSEMBLY__ =20 @@ -150,6 +153,8 @@ static inline int alternatives_text_reserved(void *star= t, void *end) } #endif /* CONFIG_SMP */ =20 +#define ALT_CALL_INSTR "call BUG_func" + #define b_replacement(num) "664"#num #define e_replacement(num) "665"#num =20 @@ -386,6 +391,10 @@ void nop_func(void); .byte \alt_len .endm =20 +.macro ALT_CALL_INSTR + call BUG_func +.endm + /* * Define an alternative between two instructions. If @feature is * present, early code in apply_alternatives() replaces @oldinstr with diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index ca25dd280b8c..e7e53b9e801b 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -395,6 +395,47 @@ noinstr void BUG_func(void) } EXPORT_SYMBOL_GPL(BUG_func); =20 +/* + * Rewrite the "call BUG_func" replacement to point to the target of the + * indirect pv_ops call "call *disp(%ip)". + */ +static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a) +{ + void *target, *bug =3D &BUG_func; + s32 disp; + + if (a->replacementlen !=3D 5 || insn_buff[0] !=3D CALL_INSN_OPCODE) { + pr_err("ALT_FLAG_DIRECT_CALL set for a non-call replacement instruction\= n"); + BUG(); + } + + if (a->instrlen !=3D 6 || instr[0] !=3D 0xff || instr[1] !=3D 0x15) { + pr_err("ALT_FLAG_DIRECT_CALL set for unrecognized indirect call\n"); + BUG(); + } + + disp =3D *(s32 *)(instr + 2); +#ifdef CONFIG_X86_64 + /* ff 15 00 00 00 00 call *0x0(%rip) */ + /* target address is stored at "next instruction + disp". */ + target =3D *(void **)(instr + a->instrlen + disp); +#else + /* ff 15 00 00 00 00 call *0x0 */ + /* target address is stored at disp. */ + target =3D *(void **)disp; +#endif + if (!target) + target =3D bug; + + /* (BUG_func - .) + (target - BUG_func) :=3D target - . */ + *(s32 *)(insn_buff + 1) +=3D target - bug; + + if (target =3D=3D &nop_func) + return 0; + + return 5; +} + /* * Replace instructions with better alternatives for this CPU type. This r= uns * before SMP is initialized to avoid SMP problems with self modifying cod= e. @@ -462,6 +503,12 @@ void __init_or_module noinline apply_alternatives(stru= ct alt_instr *start, memcpy(insn_buff, replacement, a->replacementlen); insn_buff_sz =3D a->replacementlen; =20 + if (a->flags & ALT_FLAG_DIRECT_CALL) { + insn_buff_sz =3D alt_replace_call(instr, insn_buff, a); + if (insn_buff_sz < 0) + continue; + } + for (; insn_buff_sz < a->instrlen; insn_buff_sz++) insn_buff[insn_buff_sz] =3D 0x90; =20 --=20 2.35.3