From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936080AbdKPVTj (ORCPT ); Thu, 16 Nov 2017 16:19:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29438 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934143AbdKPVTc (ORCPT ); Thu, 16 Nov 2017 16:19:32 -0500 Date: Thu, 16 Nov 2017 15:19:29 -0600 From: Josh Poimboeuf To: Juergen Gross Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Linus Torvalds , Sasha Levin , live-patching@vger.kernel.org, Jiri Slaby , Ingo Molnar , "H. Peter Anvin" , Peter Zijlstra , Mike Galbraith , Chris Wright , Alok Kataria , Rusty Russell , virtualization@lists.linux-foundation.org, Boris Ostrovsky , xen-devel@lists.xenproject.org, Thomas Gleixner , Borislav Petkov Subject: Re: [PATCH 10/13] x86/alternative: Support indirect call replacement Message-ID: <20171116211929.g4q5wa52sq64nhe5@treble> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 16 Nov 2017 21:19:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 25, 2017 at 01:25:02PM +0200, Juergen Gross wrote: > On 04/10/17 17:58, Josh Poimboeuf wrote: > > Add alternative patching support for replacing an instruction with an > > indirect call. This will be needed for the paravirt alternatives. > > > > Signed-off-by: Josh Poimboeuf > > --- > > arch/x86/kernel/alternative.c | 22 +++++++++++++++------- > > 1 file changed, 15 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 3344d3382e91..81c577c7deba 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, > > insnbuf_sz = a->replacementlen; > > > > /* > > - * 0xe8 is a relative jump; fix the offset. > > - * > > - * Instruction length is checked before the opcode to avoid > > - * accessing uninitialized bytes for zero-length replacements. > > + * Fix the address offsets for call and jump instructions which > > + * use PC-relative addressing. > > */ > > if (a->replacementlen == 5 && *insnbuf == 0xe8) { > > + /* direct call */ > > *(s32 *)(insnbuf + 1) += replacement - instr; > > - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", > > + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", > > *(s32 *)(insnbuf + 1), > > (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); > > - } > > > > - if (a->replacementlen && is_jmp(replacement[0])) > > + } else if (a->replacementlen == 6 && *insnbuf == 0xff && > > + *(insnbuf+1) == 0x15) { > > + /* indirect call */ > > + *(s32 *)(insnbuf + 2) += replacement - instr; > > + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", > > + *(s32 *)(insnbuf + 2), > > + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); > > + > > + } else if (a->replacementlen && is_jmp(replacement[0])) { > > Is this correct? Without your patch this was: > > if (*insnbuf == 0xe8) ... > if (is_jmp(replacement[0])) ... > > Now you have: > > if (*insnbuf == 0xe8) ... > else if (*insnbuf == 0xff15) ... > else if (is_jmp(replacement[0])) ... > > So only one or none of the three variants will be executed. In the past > it could be none, one or both. It can't be a call *and* a jump. It's either one or the other. Maybe it's a little confusing that the jump check uses replacement[0] while the other checks use *insnbuf? They have the same value, so the same variable should probably be used everywhere for consistency. I can make them more consistent. -- Josh From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Poimboeuf Subject: Re: [PATCH 10/13] x86/alternative: Support indirect call replacement Date: Thu, 16 Nov 2017 15:19:29 -0600 Message-ID: <20171116211929.g4q5wa52sq64nhe5@treble> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Juergen Gross Cc: Boris Ostrovsky , Rusty Russell , Mike Galbraith , xen-devel@lists.xenproject.org, Peter Zijlstra , Jiri Slaby , x86@kernel.org, linux-kernel@vger.kernel.org, Sasha Levin , Chris Wright , Thomas Gleixner , Andy Lutomirski , "H. Peter Anvin" , Borislav Petkov , live-patching@vger.kernel.org, Alok Kataria , virtualization@lists.linux-foundation.org, Linus Torvalds , Ingo Molnar List-Id: virtualization@lists.linuxfoundation.org On Wed, Oct 25, 2017 at 01:25:02PM +0200, Juergen Gross wrote: > On 04/10/17 17:58, Josh Poimboeuf wrote: > > Add alternative patching support for replacing an instruction with an > > indirect call. This will be needed for the paravirt alternatives. > > > > Signed-off-by: Josh Poimboeuf > > --- > > arch/x86/kernel/alternative.c | 22 +++++++++++++++------- > > 1 file changed, 15 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 3344d3382e91..81c577c7deba 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, > > insnbuf_sz = a->replacementlen; > > > > /* > > - * 0xe8 is a relative jump; fix the offset. > > - * > > - * Instruction length is checked before the opcode to avoid > > - * accessing uninitialized bytes for zero-length replacements. > > + * Fix the address offsets for call and jump instructions which > > + * use PC-relative addressing. > > */ > > if (a->replacementlen == 5 && *insnbuf == 0xe8) { > > + /* direct call */ > > *(s32 *)(insnbuf + 1) += replacement - instr; > > - DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", > > + DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx", > > *(s32 *)(insnbuf + 1), > > (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5); > > - } > > > > - if (a->replacementlen && is_jmp(replacement[0])) > > + } else if (a->replacementlen == 6 && *insnbuf == 0xff && > > + *(insnbuf+1) == 0x15) { > > + /* indirect call */ > > + *(s32 *)(insnbuf + 2) += replacement - instr; > > + DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx", > > + *(s32 *)(insnbuf + 2), > > + (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6); > > + > > + } else if (a->replacementlen && is_jmp(replacement[0])) { > > Is this correct? Without your patch this was: > > if (*insnbuf == 0xe8) ... > if (is_jmp(replacement[0])) ... > > Now you have: > > if (*insnbuf == 0xe8) ... > else if (*insnbuf == 0xff15) ... > else if (is_jmp(replacement[0])) ... > > So only one or none of the three variants will be executed. In the past > it could be none, one or both. It can't be a call *and* a jump. It's either one or the other. Maybe it's a little confusing that the jump check uses replacement[0] while the other checks use *insnbuf? They have the same value, so the same variable should probably be used everywhere for consistency. I can make them more consistent. -- Josh