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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B00FC0015E for ; Thu, 22 Jun 2023 18:21:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A909D8D0003; Thu, 22 Jun 2023 14:21:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A1A418D0001; Thu, 22 Jun 2023 14:21:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8BB418D0003; Thu, 22 Jun 2023 14:21:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 77DBE8D0001 for ; Thu, 22 Jun 2023 14:21:30 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 335B81401FB for ; Thu, 22 Jun 2023 18:21:30 +0000 (UTC) X-FDA: 80931201540.19.898E4A3 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf18.hostedemail.com (Postfix) with ESMTP id 0AA4F1C0025 for ; Thu, 22 Jun 2023 18:21:26 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=JkDrdCiY; dmarc=none; spf=none (imf18.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1687458087; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=t02GqixU93hABDtM3rcPTM2ZhN4nb0XzBqI30VoyYtE=; b=uDjIC4cppcotNaFEoQQQgFkAs36xvAWEq7ooujwgPy31qBkgumV5TkN3GjTIdtO0jMiUEO e3rttB+fmR7XOhoDDF+b5UuFuXS6y7cbce+3PoIpQ6u0dPxJxApx5qNGN1jrSxH/f5e4oe 0N++mHmzzBe+DaKuADcZd15llP5ujtQ= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=JkDrdCiY; dmarc=none; spf=none (imf18.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1687458087; a=rsa-sha256; cv=none; b=MOxCfJ3XtYXi2tDlxswHdU7cT+PDCtMqlV4NhFi2N+bzgClH22myEFtZ24DWGQcfhT+NX8 zU1SClr1Bj0gl48ZGiXeF7OiRtQzT4yZQXxc4vRBPaNlivQWiW3zAeEILKuEZRb9dypMRn dYXToKmDDZ8L4zx5lMPNG1HewjMi4GA= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=t02GqixU93hABDtM3rcPTM2ZhN4nb0XzBqI30VoyYtE=; b=JkDrdCiYPmkRNJ5i6MKcglC3hd NNkrYcDa/j7MYLLBgA00ey9vHiYeBuzgjsqsikSND7EtUysmHbzGMxKW0AP+vk5H3dVHHqBiPIweh gG2XM09tag/4gG9lm6S6WKfYBzWVKUyZt/0vBnCFVNR1F1vtv4X47yTkGAYwS/GvQmPjPaCVg5bKB IO7lNl1cJezXl2O0/b4/TM5Vy3oc/85fzjOG3U4XQLNicGnZsWshEqYIHbXFJ7iNj5G4E9LVEQsKi o0Cj/wcmvdiOOJIBDh7OrM2p52ajZQP5/2+eZPYS5Xl62VvDjLXmLPfcwtk0+94x48hYBrJqteI14 4sqgR3VA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qCOvX-00ForJ-LK; Thu, 22 Jun 2023 18:21:03 +0000 Date: Thu, 22 Jun 2023 19:21:03 +0100 From: Matthew Wilcox To: Rick Edgecombe Cc: x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , Weijiang Yang , "Kirill A . Shutemov" , John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com, akpm@linux-foundation.org, Andrew.Cooper3@citrix.com, christina.schimpe@intel.com, david@redhat.com, debug@rivosinc.com, szabolcs.nagy@arm.com, torvalds@linux-foundation.org, broonie@kernel.org, Yu-cheng Yu , Pengfei Xu Subject: Re: [PATCH v9 16/42] mm: Add guard pages around a shadow stack. Message-ID: References: <20230613001108.3040476-1-rick.p.edgecombe@intel.com> <20230613001108.3040476-17-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230613001108.3040476-17-rick.p.edgecombe@intel.com> X-Rspamd-Queue-Id: 0AA4F1C0025 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 7hzdbzm5m4wy5qp9dg96suwnud668aix X-HE-Tag: 1687458086-691141 X-HE-Meta: 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 JjrEF+gm bmYuuFrdRPKvwMkc0WAv4T3FVPWBYUH2cOepta4SI8czxwDN03s5/uZn0O1iheyZsfDxm9lrQlfTeFscc+OdwplTLM4jOMpQQImSlNtMJS5CLJ32P3aN7EwOAlCrG/k/yTjyyWKhNlloXJMvlGO6JltyMv8oQUyYqdVwGoen5/nUuKjoshBccMtojnklAhgtETcLN9FNQeuroM4J2s1fN9UtpNA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jun 12, 2023 at 05:10:42PM -0700, Rick Edgecombe wrote: > +++ b/include/linux/mm.h > @@ -342,7 +342,36 @@ extern unsigned int kobjsize(const void *objp); > #endif /* CONFIG_ARCH_HAS_PKEYS */ > > #ifdef CONFIG_X86_USER_SHADOW_STACK > -# define VM_SHADOW_STACK VM_HIGH_ARCH_5 /* Should not be set with VM_SHARED */ > +/* > + * This flag should not be set with VM_SHARED because of lack of support > + * core mm. It will also get a guard page. This helps userspace protect > + * itself from attacks. The reasoning is as follows: > + * > + * The shadow stack pointer(SSP) is moved by CALL, RET, and INCSSPQ. The > + * INCSSP instruction can increment the shadow stack pointer. It is the > + * shadow stack analog of an instruction like: > + * > + * addq $0x80, %rsp > + * > + * However, there is one important difference between an ADD on %rsp > + * and INCSSP. In addition to modifying SSP, INCSSP also reads from the > + * memory of the first and last elements that were "popped". It can be > + * thought of as acting like this: > + * > + * READ_ONCE(ssp); // read+discard top element on stack > + * ssp += nr_to_pop * 8; // move the shadow stack > + * READ_ONCE(ssp-8); // read+discard last popped stack element > + * > + * The maximum distance INCSSP can move the SSP is 2040 bytes, before > + * it would read the memory. Therefore a single page gap will be enough > + * to prevent any operation from shifting the SSP to an adjacent stack, > + * since it would have to land in the gap at least once, causing a > + * fault. > + * > + * Prevent using INCSSP to move the SSP between shadow stacks by > + * having a PAGE_SIZE guard gap. > + */ > +# define VM_SHADOW_STACK VM_HIGH_ARCH_5 > #else > # define VM_SHADOW_STACK VM_NONE > #endif This is a lot of very x86-specific language in a generic header file. I'm sure there's a better place for all this text.