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 4C89AC04FFE for ; Tue, 14 May 2024 04:53:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C16BE8D001A; Tue, 14 May 2024 00:53:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BC69F8D000D; Tue, 14 May 2024 00:53:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AB51C8D001A; Tue, 14 May 2024 00:53:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 8E24A8D000D for ; Tue, 14 May 2024 00:53:55 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 090DE810F0 for ; Tue, 14 May 2024 04:53:55 +0000 (UTC) X-FDA: 82115784030.03.2798A71 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf10.hostedemail.com (Postfix) with ESMTP id 3A127C001B for ; Tue, 14 May 2024 04:53:50 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=GHcFZT3E; spf=none (imf10.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1715662433; 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=LVezlibgYpYZ6gxU8jx9+3JqBMxqQ9XS0qziCKRNA3k=; b=R35ZKAweU5ZyaOkLgtY/UhvmfQzaq3Ls/uonWGuzPrbuvRP8ZEwZsxAsmtYNYT4Jk49RFM 0t1SnSAeQLPQVdUU+QL5y9AbuIp/nU8uY/FyN1NLGjoHcnWyZvaI9GXVKLJB6UypSp/BGe w/pIiayicw3dpDCZF3ysPLcRr8LgULg= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1715662433; a=rsa-sha256; cv=none; b=4H2py+uKx/mSHtMtCfM/kIHWShKxGfD7dMKcIMxHAsi233VpPHGfpgE3VaCq2gbKYyMbve cqWgp/Dmio6G54vDvXESwMY9hiOEljgvcNvwUmUVNvOG1l+OmK3ww2jkf0BKGONZ2StrlE LTfVcPBn+VCZqkMCmOXIhua4xMW5yyA= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=GHcFZT3E; spf=none (imf10.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none 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=LVezlibgYpYZ6gxU8jx9+3JqBMxqQ9XS0qziCKRNA3k=; b=GHcFZT3EnK9sb4Mi9rVI+2sDVv Npg1V0YWh2GWmyQUcGM2ZwrPwIFgaPSGKuWUayxGJ+u+k9Py6TZgLyRqnp98zYi7fpuEhezPS7wo2 gwow6wZ2o8ebmZICGDIzctqWyia4lSp29OlUv87XvkPczBX4rhL8jnyaOF+9DknOhzjSbTksg7hgv 3HmDqfaaaO6+itbk5rA6TCRqEoZuoIquxYpCt0DKHNw5LPwTSCF+PacHf7KZA3HLgI3AtjTxI0TMK jx1VDaV38PbzjoKj7OIdvZE1Q+sk41OBLxHguxb69dZKMP1pFAsYUpDlCp03Nt2Vp1dks7Q9HZUlL MlpLgvTQ==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1s6kAd-00000008jUs-2EeU; Tue, 14 May 2024 04:53:47 +0000 Date: Tue, 14 May 2024 05:53:47 +0100 From: Matthew Wilcox To: Kees Cook Cc: linux-mm@kvack.org Subject: Re: [PATCH 4/8] mm: Add __dump_folio() Message-ID: References: <20240227192337.757313-5-willy@infradead.org> <202405132126.E26FE7B9@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202405132126.E26FE7B9@keescook> X-Rspam-User: X-Stat-Signature: yjhq71nt96gihtw7qd9ubutdk7b3tgt4 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3A127C001B X-HE-Tag: 1715662430-848505 X-HE-Meta: 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 jAzUIh5W GV5/ogmVG/bp0Hq/KrB40vPC34arqSKcKV+kGq0Y1Gg7WWoeVE8qyy5MvOUSWi09NDh+SuhWhL7R6kZ3HQg+g2NhT0YFMrDhW8N/YGEHxLfSxVNq7Wh1rib4+yz99qY+uidPekatcaoApS7rbG4obIyL2peWUb+dG0TFKTy8y/0ev5lgQ3xJoda1AXg== 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: List-Subscribe: List-Unsubscribe: On Mon, May 13, 2024 at 09:33:57PM -0700, Kees Cook wrote: > Hi! > > While working on testing an improved -Warray-bounds in GCC, I encountered > this, which seems to be reasonable: Eek. I think you're right. This is a bad interaction between the page dumping code and the fixed fake head code. I will need to think about this (and LSFMM is happening right now, so I don't necessarily have a lot of time to think). I'll get back to you as soon as I can. > In file included from ./arch/x86/include/generated/asm/rwonce.h:1, > from ../include/linux/compiler.h:299, > from ../include/linux/array_size.h:5, > from ../include/linux/kernel.h:16, > from ../mm/debug.c:9: > In function 'page_fixed_fake_head', > inlined from '_compound_head' at ../include/linux/page-flags.h:251:24, > inlined from '__dump_page' at ../mm/debug.c:123:11: > ../include/asm-generic/rwonce.h:44:26: warning: array subscript 9 is outside array bounds of 'struct page[1]' [-Warray-bounds=] > 44 | #define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x)) > | ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ../include/asm-generic/rwonce.h:50:9: note: in expansion of macro '__READ_ONCE' > 50 | __READ_ONCE(x); \ > | ^~~~~~~~~~~ > ../include/linux/page-flags.h:226:38: note: in expansion of macro 'READ_ONCE' > 226 | unsigned long head = READ_ONCE(page[1].compound_head); > | ^~~~~~~~~ > ../mm/debug.c: In function '__dump_page': > ../mm/debug.c:116:21: note: at offset 72 into object 'precise' of size 64 > 116 | struct page precise; > | ^~~~~~~ > > (Not noted in this warning is that the code passes through page_folio() > _Generic macro.) > > It doesn't like that it can see that "precise" is exactly one page, so > looking at page[1] later is going to freak out. I suspect this may be > "impossible" at run-time, but I'm not 100% sure. Regardless, the compiler > can't tell. > > I suspect just making precise be a 2 page array would make this happy, > but it wasn't clear to me how such a page should be initialized. > > -Kees > > -- > Kees Cook