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 F16DAC433F5 for ; Thu, 3 Mar 2022 10:53:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232515AbiCCKyg (ORCPT ); Thu, 3 Mar 2022 05:54:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46400 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230272AbiCCKyc (ORCPT ); Thu, 3 Mar 2022 05:54:32 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8FACD177D30 for ; Thu, 3 Mar 2022 02:53:46 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 280DC1F37B; Thu, 3 Mar 2022 10:53:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1646304825; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1fQZTMimSCOOyhM5uu37na2oMa/18fIoZEJlOGor0Dc=; b=EaKUBwIE5rN3e4I89XWfER9PCH/kgIfZQt84/C0mUoEgtv4Ym6oyWm0LheMy+QAu8x5ZcI cDrL9l4vPPL9XtOt5VEQr9ltXfvTpi0ezJL0bgQdCTxd/ABdv+709AdcHPCNef4TnJT4kN k5Sh47pDMYCZ72IdwnhdbkuU2vY5v2s= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1646304825; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1fQZTMimSCOOyhM5uu37na2oMa/18fIoZEJlOGor0Dc=; b=Vs2yjuRjKTHacQLzsw8JqSHimyds3/eAM5T/sroVknPLrIZNZoHlIA/uVL/YWrMLwvBrsN dpkleBcO8r9iHPAg== Received: from pobox.suse.cz (pobox.suse.cz [10.100.2.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id C3235A3B81; Thu, 3 Mar 2022 10:53:44 +0000 (UTC) Date: Thu, 3 Mar 2022 11:53:44 +0100 (CET) From: Miroslav Benes To: Peter Zijlstra cc: x86@kernel.org, joao@overdrivepizza.com, hjl.tools@gmail.com, jpoimboe@redhat.com, andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org, ndesaulniers@google.com, keescook@chromium.org, samitolvanen@google.com, mark.rutland@arm.com, alyssa.milburn@intel.com, rostedt@goodmis.org, mhiramat@kernel.org, alexei.starovoitov@gmail.com Subject: Re: [PATCH v2 33/39] objtool: Add IBT/ENDBR decoding In-Reply-To: <20220224151323.959862564@infradead.org> Message-ID: References: <20220224145138.952963315@infradead.org> <20220224151323.959862564@infradead.org> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Thu, 24 Feb 2022, Peter Zijlstra wrote: > Decode ENDBR instructions and WARN about NOTRACK prefixes. I guess it has been already mentioned somewhere, but could you explain NOTRACK prefix here, please? If I understand it right, it disables IBT for the indirect branch instruction meaning that its target does not have to start with ENDBR? > Signed-off-by: Peter Zijlstra (Intel) > --- > tools/objtool/arch/x86/decode.c | 34 +++++++++++++++++++++++++++++----- > tools/objtool/include/objtool/arch.h | 1 + > 2 files changed, 30 insertions(+), 5 deletions(-) > > --- a/tools/objtool/arch/x86/decode.c > +++ b/tools/objtool/arch/x86/decode.c > @@ -103,6 +103,18 @@ unsigned long arch_jump_destination(stru > #define rm_is_mem(reg) (mod_is_mem() && !is_RIP() && rm_is(reg)) > #define rm_is_reg(reg) (mod_is_reg() && modrm_rm == (reg)) > > +static bool has_notrack_prefix(struct insn *insn) > +{ > + int i; > + > + for (i = 0; i < insn->prefixes.nbytes; i++) { > + if (insn->prefixes.bytes[i] == 0x3e) > + return true; > + } > + > + return false; > +} > + ... > @@ -636,20 +656,24 @@ int arch_decode_instruction(struct objto > break; > > case 0xff: > - if (modrm_reg == 2 || modrm_reg == 3) > + if (modrm_reg == 2 || modrm_reg == 3) { > > *type = INSN_CALL_DYNAMIC; > + if (has_notrack_prefix(&insn)) > + WARN("notrack prefix found at %s:0x%lx", sec->name, offset); > > - else if (modrm_reg == 4) > + } else if (modrm_reg == 4) { > > *type = INSN_JUMP_DYNAMIC; > + if (has_notrack_prefix(&insn)) > + WARN("notrack prefix found at %s:0x%lx", sec->name, offset); And we want to warn about it here so that we can have it all in the kernel control? Miroslav