From mboxrd@z Thu Jan 1 00:00:00 1970 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 1904ECE79DC for ; Wed, 20 Sep 2023 14:45:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235237AbjITOpu (ORCPT ); Wed, 20 Sep 2023 10:45:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236835AbjITOpJ (ORCPT ); Wed, 20 Sep 2023 10:45:09 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 87840C6 for ; Wed, 20 Sep 2023 07:45:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4hBA0mBFz86EuPBzuRyC6ZCKI5h6ySdd8K4qpgeL0oM=; b=Jsv7w/BZMh+zkv/M4Ojx8yDNnZ Z6rZzuzcqV9vBeGcpupMFe4Yg7c34Dvkk9NY7HugdGXloG8jpgcsxjBj449PLlFWWfqFIDxpw5F8d DGU7GgKsk5pEwwGXqIevo+moJCeGwFLsfHPaOSf1atcOjN6+YRWg9NWvqBA1gvMM2K/WAvPzglpt2 w34nqJi9OBXzG1MbMlFiCc6XV+6OiBOaWQR0asifD9ycEhqxAlQP6JAj/lmaXwMWo8D0xSiSoIeNc +rjoRppbtLbusWfeA/M5HHtyJg0ODokI8yGkWERlBZ3BxIIVIpe/BujHHPph75zZABA4/bS+qpf6x re1627Dw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1qiyRK-00EfRD-2z; Wed, 20 Sep 2023 14:44:32 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 09E03300513; Wed, 20 Sep 2023 16:44:32 +0200 (CEST) Date: Wed, 20 Sep 2023 16:44:31 +0200 From: Peter Zijlstra To: Juergen Gross Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Subject: Re: [RFC PATCH 2/3] x86/alternative: add indirect call patching Message-ID: <20230920144431.GA6687@noisy.programming.kicks-ass.net> References: <20230608140333.4083-1-jgross@suse.com> <20230608140333.4083-3-jgross@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230608140333.4083-3-jgross@suse.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 08, 2023 at 04:03:32PM +0200, Juergen Gross wrote: > 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 Since I wrecked all that with 270a69c4485d ("x86/alternative: Support relocations in alternatives") I wrote you a replacement :-) --- Index: linux-2.6/arch/x86/include/asm/alternative.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/alternative.h +++ linux-2.6/arch/x86/include/asm/alternative.h @@ -10,6 +10,9 @@ #define ALT_FLAG_NOT (1 << 0) #define ALT_NOT(feature) ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature)) +#define ALT_FLAG_CALL (1 << 1) +#define ALT_CALL(feature) ((ALT_FLAG_CALL << ALT_FLAGS_SHIFT) | (feature)) +#define ALT_CALL_ALWAYS ALT_CALL(X86_FEATURE_ALWAYS) #ifndef __ASSEMBLY__ @@ -150,6 +153,8 @@ static inline int alternatives_text_rese } #endif /* CONFIG_SMP */ +#define ALT_CALL_INSTR "call x86_BUG" + #define b_replacement(num) "664"#num #define e_replacement(num) "665"#num Index: linux-2.6/arch/x86/kernel/alternative.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/alternative.c +++ linux-2.6/arch/x86/kernel/alternative.c @@ -396,6 +396,40 @@ noinstr void x86_BUG(void) EXPORT_SYMBOL_GPL(x86_BUG); /* + * Rewrite the "call x86_BUG" 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 = &x86_BUG; + + if (a->replacementlen != 5 || insn_buff[0] != CALL_INSN_OPCODE) { + pr_err("Alternative: ALT_FLAG_CALL set for a non-call replacement instruction\n"); + pr_err(" Ignoring the flag for the instruction at %pS (%px)\n", instr, instr); + return 5; + } + + if (a->instrlen != 6 || instr[0] != 0xff || instr[1] != 0x15) { + pr_err("Alternative: ALT_FLAG_CALL set for unrecognized indirect call\n"); + pr_err(" Not replacing the instruction at %pS (%px)\n", instr, instr); + return -1; + } + + /* ff 15 00 00 00 00 call *0x0(%rip) */ + target = *(void **)(instr + a->instrlen + *(s32 *)(instr + 2)); + if (!target) + target = bug; + + /* (x86_BUG - .) + (target - x86_BUG) := target - . */ + *(s32 *)(insn_buff + 1) += target - bug; + + if (target == &x86_nop) + return 0; + + return 5; +} + +/* * Replace instructions with better alternatives for this CPU type. This runs * before SMP is initialized to avoid SMP problems with self modifying code. * This implies that asymmetric systems where APs have less capabilities than @@ -451,6 +485,12 @@ void __init_or_module noinline apply_alt memcpy(insn_buff, replacement, a->replacementlen); insn_buff_sz = a->replacementlen; + if (a->flags & ALT_FLAG_CALL) { + insn_buff_sz = 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] = 0x90;