From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6D1B9351C20; Wed, 29 Apr 2026 13:57:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777471030; cv=none; b=UeWVWHoqvi6E+5qcjUMuQ3OwGgHSXCOMmegC7T0Tyr8IfzPcf6/GWmrPKkT5wAzwdscz6eTf+SHHYann4KrkTDnDWFlY1yCQCG5zz/YEVJsQ1qu3tXjcM0L11ziwRu5chvU9e1e4ggr+Q68GC4WOKVjg7oXPJpiYLV3EOgVLj/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777471030; c=relaxed/simple; bh=uCnIw3CR1viWizfBhTu1oz/vcz1koGemFdz8oEqehX4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eG+Jj6IO2knSTflBbVpM/lp1xBohBAVMtoeiycKH0dmb86m8TTBe+0G3RmTdySSp2Ou8V+KrRBN7RW221toEA9MkrvUIt+LPl1XhGyiX1U5rdgctsKzz/rTGl8RIlIvvxlIUR1wO/5KlPtyMzeJ8+SBjIcl0OZdaEdkAiZ/m9Vs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=tKo7qpcU; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="tKo7qpcU" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A4E251650; Wed, 29 Apr 2026 06:57:01 -0700 (PDT) Received: from [10.57.62.76] (unknown [10.57.62.76]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2D89E3F62B; Wed, 29 Apr 2026 06:57:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777471027; bh=uCnIw3CR1viWizfBhTu1oz/vcz1koGemFdz8oEqehX4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tKo7qpcUs76IDv6e5R8HeijntK+tVAsQf3L1gGheC7KBuQnvLjzEHiTDybDxbZD8Z PtAB4aUFl6moEHsC3wTckysjYxLPrEqXAKhGTICBGzpyQ8QAG/d2fCSGec37wtX7SN 2lIFCIl0BQq9yN+RECGiSkBoDunVzSNSdbxs6Lhk= Message-ID: <961e9d06-1520-4176-ad76-3f0d8d5ab146@arm.com> Date: Wed, 29 Apr 2026 15:57:01 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 14/15] arm64: mm: Generalize manipulation code of read-only descriptors To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-31-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260427153416.2103979-31-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 27/04/2026 17:34, Ard Biesheuvel wrote: > [...] > > -void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) > +void noinstr set_rodata_pte(pte_t *ptep, pte_t pte) > { > - pgd_t *fixmap_pgdp; > + pte_t *fixmap_ptep; > > /* > - * Don't bother with the fixmap if swapper_pg_dir is still mapped > - * writable in the kernel mapping. > + * Don't bother with the fixmap if rodata is still mapped > + * writable in the kernel and linear mappings. > */ > if (rodata_is_rw) { > - WRITE_ONCE(*pgdp, pgd); > + WRITE_ONCE(*ptep, pte); > dsb(ishst); > isb(); > return; > } > > - spin_lock(&swapper_pgdir_lock); > - fixmap_pgdp = pgd_set_fixmap(__pa_symbol(pgdp)); > - WRITE_ONCE(*fixmap_pgdp, pgd); > + spin_lock(&rodata_pgdir_lock); > + fixmap_ptep = pte_set_fixmap(__pa_nodebug(ptep)); I don't know much about the fixmap but it strikes me as odd that we would now use pte_set_fixmap() at all levels. I suppose the question is whether swapper_pg_dir could be written concurrently with fixmap page tables at PMD level or above? I'm also wondering if those fixmap page tables are ever written to. - Kevin > + WRITE_ONCE(*fixmap_ptep, pte); > /* > * We need dsb(ishst) here to ensure the page-table-walker sees > * our new entry before set_p?d() returns. The fixmap's > * flush_tlb_kernel_range() via clear_fixmap() does this for us. > */ > - pgd_clear_fixmap(); > - spin_unlock(&swapper_pgdir_lock); > + pte_clear_fixmap(); > + spin_unlock(&rodata_pgdir_lock); > } > > [...]