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 X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69DA1C433E0 for ; Tue, 26 Jan 2021 12:24:51 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 22F922255F for ; Tue, 26 Jan 2021 12:24:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 22F922255F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=pp0pRKW6gsw7P97W2GoJGl2SHaZuvxPuliwk1HmzOmw=; b=1s3H/aNTkVQU9mOLkoNFNWAv7 zr4MYLBHVIMfhOhX5orVTiWgu1Q2dkaqc2qJWTFsEHknPjmUsVeIBV3kFdbaQ3+FpSVhBRqaR5TFI 7N2ol69PPHY9qiL+PycpFPPqrufQGWcP1sV6J+dOuMa64NUQxIOeloGmvTxXN4UVN7zpMeg7CImGP 2IDVYgyeG75qJyRjFlcKBZeUCnLmXVbdyceNb2PGRWRkvLF/cr/KpnD40OBys1COcD7CgxfKxyR2C bqtCRz2Nq7egf1K8vnkd5Ds6BizuJPognNHbKLGWU2a5LkGrt3lLjFI2dAxo05uCFHGUVBfPbW7uH vjMY8YgDA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4NNi-0006SK-HZ; Tue, 26 Jan 2021 12:23:38 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4NNg-0006Rk-0N for linux-arm-kernel@lists.infradead.org; Tue, 26 Jan 2021 12:23:37 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 51CFD2255F; Tue, 26 Jan 2021 12:23:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611663815; bh=Txadf1GVGZmuiWIiwNvXwwDCn/RQcQ+HKSyv+CMIrNg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OPnMOHUAfmBpDH08dsoErR2m4t/+7QqnRRWjR69lUT8lqeqZPIgPSrXhbwJ198zXh fvSn4SHgFeddSAxqcnE/q7TYEHksaTMFOIpTbWuPAFEIzP1COYUKUN/Lm/ixmKfiBw DrRVk5tw4R3N4PujpSljkLA5AoGEINRmbNthf7WDFedrILfrX42mB3xENBr4RSW4Os wCALocxR4nga/3mE+xrk4Qp9WFev3WctB9sW7wFT6wVyEmwBRcJKqSNphr/rQSn02s 9UhdECB9atuI7GnQi7ab0cqR4ZhTqD9SYUvhYep/+MHQaKuUeY3p0fHuqliEW7b5Xg r94jZ5qNNLEZw== Date: Tue, 26 Jan 2021 12:23:31 +0000 From: Will Deacon To: Catalin Marinas Subject: Re: [PATCH v3 1/2] arm64: Support execute-only permissions with Enhanced PAN Message-ID: <20210126122330.GA29613@willie-the-truck> References: <20210119160723.116983-1-vladimir.murzin@arm.com> <20210119160723.116983-2-vladimir.murzin@arm.com> <20210126110305.GA29467@willie-the-truck> <20210126120542.GA20158@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210126120542.GA20158@gaia> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210126_072336_189815_E2705A1B X-CRM114-Status: GOOD ( 34.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Vladimir Murzin , keescook@chromium.org, linux-arm-kernel@lists.infradead.org, dave.martin@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 26, 2021 at 12:05:42PM +0000, Catalin Marinas wrote: > On Tue, Jan 26, 2021 at 11:03:06AM +0000, Will Deacon wrote: > > On Tue, Jan 19, 2021 at 04:07:22PM +0000, Vladimir Murzin wrote: > > > #define pte_valid_not_user(pte) \ > > > - ((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID) > > > + ((pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN)) > > > #define pte_valid_user(pte) \ > > > ((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER)) > > > > Won't pte_valid_user() go wrong for exec-only mappings now? > > I wondered about the same in November (and reproducing my comment > below): > > https://lore.kernel.org/linux-arm-kernel/20201119182236.GN4376@gaia/ > > pte_valid_user() checks for both PTE_VALID and PTE_USER. In theory, a > !PTE_UXN is also user-accessible but it's only used in gup_pte_range() > via pte_access_permitted(). If "access" in the latter means only > read/write, we should be ok. If we keep it as is, a comment would > be useful. I think we should ensure that: pte_valid(pte) && (pte_valid_not_user(pte) || pte_valid_user(pte)) is always true, but I don't think it is after this patch. It reminds me of some of the tests that Anshuman wrote. > > > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h > > > index 8b5e7e5..47e9fdc 100644 > > > --- a/arch/arm64/include/asm/sysreg.h > > > +++ b/arch/arm64/include/asm/sysreg.h > > > @@ -591,6 +591,7 @@ > > > (SCTLR_EL2_RES1 | ENDIAN_SET_EL2) > > > > > > /* SCTLR_EL1 specific flags. */ > > > +#define SCTLR_EL1_EPAN (BIT(57)) > > > #define SCTLR_EL1_ATA0 (BIT(42)) > > > > > > #define SCTLR_EL1_TCF0_SHIFT 38 > > > @@ -631,7 +632,7 @@ > > > SCTLR_EL1_SED | SCTLR_ELx_I | SCTLR_EL1_DZE | SCTLR_EL1_UCT | \ > > > SCTLR_EL1_NTWE | SCTLR_ELx_IESB | SCTLR_EL1_SPAN | SCTLR_ELx_ITFSB | \ > > > SCTLR_ELx_ATA | SCTLR_EL1_ATA0 | ENDIAN_SET_EL1 | SCTLR_EL1_UCI | \ > > > - SCTLR_EL1_RES1) > > > + SCTLR_EL1_EPAN | SCTLR_EL1_RES1) > > > > Why is this handled differently to normal PAN, where the SCTLR is written in > > cpu_enable_pan()? > > That's how it was done in an early version but I suggested we move it to > the default SCTLR bits to save some lines: > > https://lore.kernel.org/linux-arm-kernel/20201202182303.GC21091@gaia/ > > With classic PAN, we only enable it if all the CPUs support it. For EPAN > that's not necessary since EPAN should depend on PAN being enabled. Ok, let's just hope we don't have any CPU errata requiring us to disable it. > It's also cached in the TLB, so it's a bit of a hassle with CnP. See > this past discussion: > > https://lore.kernel.org/linux-arm-kernel/X7P+r%2Fl3ewvaf1aV@trantor/ Thanks. None of this is in the Arm ARM afaict, so I can't figure this stuff out on my own. > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > index 3c40da4..c32095f6 100644 > > > --- a/arch/arm64/mm/fault.c > > > +++ b/arch/arm64/mm/fault.c > > > @@ -529,6 +529,9 @@ static int __kprobes do_page_fault(unsigned long far, unsigned int esr, > > > if (faulthandler_disabled() || !mm) > > > goto no_context; > > > > > > + if (cpus_have_const_cap(ARM64_HAS_EPAN)) > > > + vm_flags &= ~VM_EXEC; > > > > This needs a comment, and I think it would be cleaner to rework the vm_flags > > initialisation along the lines of: > > > > unsigned long vm_flags; > > unsigned long mm_flags = FAULT_FLAG_DEFAULT; > > > > if (user_mode(regs)) > > mm_flags |= FAULT_FLAG_USER; > > > > if (is_el0_instruction_abort(esr)) { > > vm_flags = VM_EXEC; > > mm_flags |= FAULT_FLAG_INSTRUCTION; > > } else if (is_write_abort(esr)) { > > vm_flags = VM_WRITE; > > mm_flags |= FAULT_FLAG_WRITE; > > } else { > > vm_flags = VM_READ | VM_WRITE; > > if (!cpus_have_const_cap(ARM64_HAS_EPAN)) > > vm_flags |= VM_EXEC: > > } > > > > (but again, please add a comment to that last part because I still don't > > really follow what you're doing) > > Every time I come across this vm_flags handling I have to spend some > minutes to re-understand what it does. So vm_flags tells us what bits we > must have in vma->vm_flags for the fault to be benign. But we start with > all rwx flags and clear VM_EXEC if EPAN since exec does not imply read, > making it more confusing. > > I think your rewrite is cleaner, maybe with some comment why we add > VM_EXEC when !EPAN. Agreed. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel