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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 663ADC88E4A for ; Fri, 11 Sep 2026 01:25:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:CC:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=c58X8ecI9cB05ly16RbhbStXD3+pVr/Huxc1EWTQbes=; b=tmpUajZXYda1ZHxNeGCRTAbTrW 1duxkEbjdb3y6W63PxcH6iiWn7zRYv6YqFsM39Daj2Jn9+Dn23eYGRZiH+uhos5ARSTzbsqaAsieW JQy67zzrxATSWqgfjSz6iKWtyJ/Ri0dLKXPPj+09Kwd5Z09KcwkKqQxt4ZJZD2L3dXm8DQ5l5Fjcx xVONfXsqw0cpenBUTNVnCBjZxYCm4fec0tZdI7sLvzdl1bJsrHLfYJj6SNxZMpwzQd70K067rDAu0 7bq778822ZnwHz1uSjNAFnH2jf/bftXC05cI17RRlU8uT168d1e9+aLU6hM/O+z5KWE/T8ti4UCNu dsUa+yBg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4q14-0000000Ff3U-0E55; Fri, 11 Sep 2026 01:25:22 +0000 Received: from canpmsgout06.his.huawei.com ([113.46.200.221]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4q10-0000000Ff2t-2iWB for linux-arm-kernel@lists.infradead.org; Fri, 11 Sep 2026 01:25:20 +0000 dkim-signature: v=1; a=rsa-sha256; d=h-partners.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=c58X8ecI9cB05ly16RbhbStXD3+pVr/Huxc1EWTQbes=; b=hKeFIytpUKGNGHnKNt+jVrk28bOpl+Wbb2Y6jJ3uatSCB9pPzYr0PPze44XkpVSMy3dDfi69H Y383P3yvjSetY0Ley0mwqbo4kDMRMUuXcfUqWYF3RS0iNv9p35fOyWMFRyupylbneMH1cCqMKRr vNiSJxXQxfvS5SpUuj2UDLA= Received: from mail.maildlp.com (unknown [172.19.163.0]) by canpmsgout06.his.huawei.com (SkyGuard) with ESMTPS id 4hgxQT0JHczRhXP; Fri, 11 Sep 2026 09:14:09 +0800 (CST) Received: from kwepemf100008.china.huawei.com (unknown [7.202.181.222]) by mail.maildlp.com (Postfix) with ESMTPS id 19B1540561; Fri, 11 Sep 2026 09:25:02 +0800 (CST) Received: from [10.174.179.37] (10.174.179.37) by kwepemf100008.china.huawei.com (7.202.181.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Fri, 11 Sep 2026 09:25:01 +0800 Message-ID: <18e70561-f2d1-444c-00d3-97093bd1bb5e@huawei.com> Date: Fri, 11 Sep 2026 09:25:00 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH] arm64: io: Reject present-invalid user prot in ioremap_prot() Content-Language: en-US To: Catalin Marinas , Will Deacon CC: , , , , , , References: <20260905033148.3657516-1-zengheng@huaweicloud.com> From: Zeng Heng In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.37] X-ClientProxiedBy: kwepems200002.china.huawei.com (7.221.188.68) To kwepemf100008.china.huawei.com (7.202.181.222) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260910_182519_021293_6F3F66B2 X-CRM114-Status: GOOD ( 19.97 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Catalin, On 2026/9/10 1:07, Catalin Marinas wrote: > On Wed, Sep 09, 2026 at 02:04:50PM +0100, Will Deacon wrote: >> On Wed, Sep 09, 2026 at 01:50:09PM +0100, Catalin Marinas wrote: >>> On Sat, Sep 05, 2026 at 11:31:48AM +0800, Zeng Heng wrote: >>>> From: Zeng Heng >>>> >>>> Mapping a stack-top page via /dev/mem with PROT_NONE and then reading >>>> that process's /proc//cmdline triggers a spurious WARN in >>>> ioremap_prot() through generic_access_phys(): >>>> >>>> WARNING: ./arch/arm64/include/asm/io.h:275 at generic_access_phys >>>> Call trace: >>>> generic_access_phys+0x1c8/0x228 (P) >>>> __access_remote_vm+0x2b4/0x398 >>>> access_remote_vm+0x14/0x30 >>>> get_mm_cmdline+0xf8/0x2a0 >>>> proc_pid_cmdline_read+0x68/0x120 >>>> >>>> generic_access_phys() passes the full pgprot derived from the user PTE >>>> to ioremap_prot(). A PROT_NONE /dev/mem mapping is encoded as PAGE_NONE, >>>> which clears PTE_VALID and sets the software PTE_PRESENT_INVALID bit. >>>> On arm64 such an entry is still pte_present(), so follow_pfnmap_start() >>>> reports the pfn and generic_access_phys() reaches ioremap_prot(). >>>> The PTE_USER assertion, which is meant to catch kernel prots being >>>> passed by mistake, then fires for a PROT_NONE user mapping >>>> that legitimately lacks PTE_USER, producing the spurious WARN. >>>> >>>> Reject a user prot encoding a present-invalid (i.e. PROT_NONE) entry up >>>> front so that generic_access_phys() cleanly fails the access instead >>>> of warning. Note that PTE_PRESENT_INVALID aliases the PTE_NG bit and >>>> is only meaningful when PTE_VALID is clear, so both bits must be >>>> checked together. >>>> >>>> Fixes: 8f098037139b ("arm64: io: Extract user memory type in ioremap_prot()") >>>> Signed-off-by: Zeng Heng >>>> --- >>>> arch/arm64/include/asm/io.h | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h >>>> index 21c8e400107c..bbfbc4682639 100644 >>>> --- a/arch/arm64/include/asm/io.h >>>> +++ b/arch/arm64/include/asm/io.h >>>> @@ -272,6 +272,10 @@ static inline void __iomem *ioremap_prot(phys_addr_t phys, size_t size, >>>> pgprot_t prot; >>>> ptval_t user_prot_val = pgprot_val(user_prot); >>>> >>>> + if ((user_prot_val & (PTE_VALID | PTE_PRESENT_INVALID)) == >>>> + PTE_PRESENT_INVALID) >>>> + return NULL; >>>> + >>>> if (WARN_ON_ONCE(!(user_prot_val & PTE_USER))) >>>> return NULL; >>> I wonder whether we should just drop the warning and return NULL if >>> !PTE_USER && PTE_UXN. The latter check would also catch execute-only >>> mappings (Sashiko pointed out this case still trips the warning). The >>> PROT_NONE case would be covered automatically as well since PTE_USER is >>> cleared, PTE_UXN set. Maybe add a comment that that pte_protnone() >>> relies on !PTE_USER && PTE_UXN, so it's not that we avoid the PROT_NONE >>> issue by chance. >> Hmm, do we want exec-only mappings to be readable via /dev/mem? > Ah, yes, got confused on how it reaches this path. It doesn't make sense > to allow exec-only to be readable. Also if we mmap(PROT_EXEC) /dev/mem, > PTE_UXN ends up set anyway via pgprot_noncached(). But it does have > PTE_VALID, so the above won't catch it. > > Checking !PTE_USER should be sufficient here and return NULL. For the > warning, I think we can check PTE_NG first but it only works without > kpti. Thanks for your reply. I agree that checking PTE_USER is sufficient here. I'll drop the WARN_ON_ONCE() and return NULL directly when PTE_USER is not set. And I won't add a PTE_NG check for the warning since, as you pointed out, that would not work reliably with KPTI. Best regards, Zeng Heng