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 25404C001B0 for ; Sat, 12 Aug 2023 02:57:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236099AbjHLC52 (ORCPT ); Fri, 11 Aug 2023 22:57:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40972 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235412AbjHLC5Z (ORCPT ); Fri, 11 Aug 2023 22:57:25 -0400 Received: from mail-pf1-x449.google.com (mail-pf1-x449.google.com [IPv6:2607:f8b0:4864:20::449]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45F553581 for ; Fri, 11 Aug 2023 19:57:24 -0700 (PDT) Received: by mail-pf1-x449.google.com with SMTP id d2e1a72fcca58-686e7b27f55so3359573b3a.2 for ; Fri, 11 Aug 2023 19:57:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1691809044; x=1692413844; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=tS5bjxGvXHgpjsR89BBAVK24EK+MfHyO8qai22TwsEE=; b=0xRjApE/U2RYFS+YWsLHyC/7iP6MlrHOrokf6+FnoBtk43mlqfsrwUv8M/FWPvEMxR n/IlPK4ZSgwFLSbugSEe11CEcWK596MYNaTc12vJSoAXiB1Q1S7E8n37GfCZUNiVvLzI mRF9H2wv+hFDorBRRf0l7Sw+fQIW7GKXBv+wgFEO59Y6UibZvqkgqZo5NUb1VE42c153 /A+4DJCLf+ZnVVCqjLqNnGQGAo6FN6HMe3AJ52aiNQVCOQjPj7XO79l+tXRnicRvwlOn T6m2ifmiho+Xy1m3EYbG0oKMwPo60tZZE6K5+uLlTIsCqNkCdnZkE3mujYPrz/swJMoL SLng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691809044; x=1692413844; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=tS5bjxGvXHgpjsR89BBAVK24EK+MfHyO8qai22TwsEE=; b=LRWYcaQbEztBJJfoVAm6tbue92dR3wLosBKeu9+SispM+Mcaq7WJohEOgh2W6kmgez TNnN3Q1vMJZN+dHXobB+OwWBefxQmCUJ1Y7Sn46J1lbE/BN7bWO99J/40XmRrTAjNLdF 87VoKi1Rx3xGOVCRWe0+9OquXDOK055BAVRu7vZK0nYSYTC1tNGOfKjv5ry7VBUSlwD3 H0L6qN4DtTYPKoMW0yAQOnEYcPMpWEUiJPYYE7+KPOdDRuhrFwT+9A5EGgfzfek6ceQ9 TOwQrU3TzOOaYAC4PGP7JgYiqQ6gf9y/f126LwAkfEtpOMBvn3HgNHVZvwBWPKYBtdFJ VPxw== X-Gm-Message-State: AOJu0YwUw+ECiQ5Q9qG6hLz8bW2Cr1R9uSs7kAD+YQBqCgG2XqhYja4l stQRfE8gffSJLHV4Hk5UAtMuILj+hH8= X-Google-Smtp-Source: AGHT+IFUZBQeQ6IXU+PWByB0C9HZCEmzHADTXcVvXMNbSAzt3QPkvaokh4WVr9x/O5cMStF3DhjL4D6etL0= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:3928:b0:686:df16:f887 with SMTP id fh40-20020a056a00392800b00686df16f887mr1611366pfb.6.1691809043752; Fri, 11 Aug 2023 19:57:23 -0700 (PDT) Date: Fri, 11 Aug 2023 19:57:22 -0700 In-Reply-To: <8edc91f9-ce20-9528-a496-5b6e650bb63f@redhat.com> Mime-Version: 1.0 References: <20230811155255.250835-1-seanjc@google.com> <8edc91f9-ce20-9528-a496-5b6e650bb63f@redhat.com> Message-ID: Subject: Re: [PATCH] x86/retpoline: Don't clobber RFLAGS during srso_safe_ret() From: Sean Christopherson To: "Mika =?utf-8?B?UGVudHRpbMOk?=" Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, linux-kernel@vger.kernel.org, Srikanth Aithal , kvm@vger.kernel.org, Paolo Bonzini Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 11, 2023, Mika Penttil=C3=A4 wrote: > > @@ -252,11 +252,10 @@ SYM_START(srso_untrain_ret, SYM_L_GLOBAL, SYM_A_N= ONE) > > .byte 0x48, 0xb8 > > SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL) > > - add $8, %_ASM_SP > > + lea 8(%_ASM_SP), %_ASM_SP > > ret > > int3 > > int3 > > - int3 > > lfence > > call srso_safe_ret > > int3 > >=20 > > base-commit: 25aa0bebba72b318e71fe205bfd1236550cc9534 >=20 > Don't we have the same kind of problems with __x86_return_skl ? Yep, forcing that path via "retbleed=3Dforce retbleed=3Dstuff spectre_v2=3D= retpoline,generic" yields the same failures. I have no idea how to go about cleanly fixing th= at. The logic effectively requires modifying flags, the only thing I can think = of is to save/restore flags across the thunk, which seems beyond gross. Given that no one has complained about this, I think I'd vote to simply dis= able KVM if call depth tracking is being used.