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 F2346C433EF for ; Mon, 2 May 2022 20:17:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1387263AbiEBUVV (ORCPT ); Mon, 2 May 2022 16:21:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352110AbiEBUVP (ORCPT ); Mon, 2 May 2022 16:21:15 -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 1B0EFBF73 for ; Mon, 2 May 2022 13:17:46 -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=Llu4EhFfyri9boZWF9UgcWQJbPBw0lrtewWWD268xjw=; b=R5Zfmcz6hlUxJGb+EcNuY6xfWQ W2uFkszEspHYYH4k/j//5ejjaFiYqYYx2dyd7OqN4mUGQZXR8lLvxPkAsdx1JPQ9O0aXy45hK8/YS hiAuL6q2HZMGfYnAze0Li6lTT2nAZbQMpsdzSXw4C0RtmIcEa8BJC4oGkRpyxoBq7FV3QxihZVR8v 2QmLaiIrnf3bjX15vZZW6eI8I94IpAxYF6wbMxrhZEyViXR9z83bOZZ00Oa0J6UbPQEJsB2gIdzfP 4oVRcZwYQ73PbZbuzI/c+iVuzS9MmWB6b6me4iZ45HnrSr09Lu3gGeE49BJUhCF0xL87GxV5blKsc 8MxI3r6Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nlcUG-00AZn4-6h; Mon, 02 May 2022 20:17:40 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id CD663300091; Mon, 2 May 2022 22:17:39 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B891220288CEB; Mon, 2 May 2022 22:17:39 +0200 (CEST) Date: Mon, 2 May 2022 22:17:39 +0200 From: Peter Zijlstra To: Josh Poimboeuf Cc: x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] objtool: Fix SLS checks Message-ID: References: <20220502181547.fzz2yre2p4akph4s@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220502181547.fzz2yre2p4akph4s@treble> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 02, 2022 at 11:15:47AM -0700, Josh Poimboeuf wrote: > From: Josh Poimboeuf > Subject: [PATCH] x86/speculation: Mitigate SLS for JMP_NOSPEC with retpolines disabled > > Having disabled retpolines doesn't necessarily mean the user doesn't > care about straight-line speculation. For example, retpolines are > disabled when eIBRS is used. > > If CONFIG_SLS is enabled, properly mitigate SLS for JMP_NOSPEC for the > retpolines disabled cases. > > Signed-off-by: Josh Poimboeuf > --- > arch/x86/include/asm/nospec-branch.h | 13 ++++++++++--- > tools/objtool/check.c | 3 --- > 2 files changed, 10 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > index acbaeaf83b61..0648746bf60b 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -75,6 +75,13 @@ > .popsection > .endm > > +.macro INDIRECT_JMP reg > + jmp *%\reg > +#ifdef CONFIG_SLS > + int3 > +#endif > +.endm > + > /* > * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple > * indirect jmp/call which may be susceptible to the Spectre variant 2 > @@ -82,11 +89,11 @@ > */ > .macro JMP_NOSPEC reg:req > #ifdef CONFIG_RETPOLINE > - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ > + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), \ > __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \ > - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE > + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), X86_FEATURE_RETPOLINE_LFENCE > #else > - jmp *%\reg > + INDIRECT_JMP \reg > #endif > .endm > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > index e7983c3e2408..3cf3ad0b5db5 100644 > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -3842,9 +3842,6 @@ static int validate_sls(struct objtool_file *file) > for_each_insn(file, insn) { > next_insn = next_insn_same_sec(file, insn); > > - if (insn->retpoline_safe) > - continue; > - > switch (insn->type) { > case INSN_RETURN: > if (!next_insn || next_insn->type != INSN_TRAP) { Yes, agreed. But perhaps with something like this on top? --- diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 3c66073e7645..84beeb5297d5 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -452,6 +452,17 @@ static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes) return ret; i += ret; +#ifdef CONFIG_SLS + /* + * Ideally this would be unconditional, except in case of + * RETPOLINE_LFENCE we don't have sufficient space. Additionally, + * -mharden-sls=all should be extended to emit INT3 after + * direct jumps too, which will then cover that case. + */ + if (i < insn->length) + bytes[i++] = INT3_INSN_OPCODE; +#endif + for (; i < insn->length;) bytes[i++] = BYTES_NOP1; diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index b2b2366885a2..26e742da3129 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -33,9 +33,9 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL) UNWIND_HINT_EMPTY ANNOTATE_NOENDBR - ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \ + ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), \ __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \ - __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE + __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; INDIRECT_JMP \reg), X86_FEATURE_RETPOLINE_LFENCE .endm diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 16b6efacf7c6..6929856e7f6d 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -418,6 +418,10 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip) #endif EMIT2(0xFF, 0xE0 + reg); +#ifdef CONFIG_SLS + EMIT1(0xCC); +#endif + *pprog = prog; }