From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2A943396D15 for ; Thu, 3 Sep 2026 09:23:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788427386; cv=none; b=OWMXDvdlSE3wTEfpboJRQuCw+tXVySKTq8M1lHpOaBMPVBlR5pGkpE2Dt8A7Ia5TmvUtCMUfGfAlxT0kvCv/pdUd3z5yahiivHOaHTcTmBLZ9+9VR1UqPz303W9SdskY+7FHHtn43mgETkhDhAT9RGYjEJ1SH6FLOhelGGPL7V4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788427386; c=relaxed/simple; bh=QJzTl9mpfbcR/ern5So2dPo/+BdDFUSyA8/TbaT21bI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FzK+aXxKLfoUb65Sxa6F9Bw1hwj2Q4K4TyuxWc0BeRtC/XbP/F5twLL+PNZEQCeb0WoIs2gdQf8SrdgzSjpVhy4V2fMLKZRRvPagoRnRyjNI781R7kDNEgA3sQiNPrCjZFv7eEZ8kbTBVc2AFecMOvh13bAzRU9l6sf9QqF+hxQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CsLTmwDY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CsLTmwDY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 969871F000E9; Thu, 3 Sep 2026 09:22:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788427376; bh=CVH46s0TiBnSL1nhlyLYQT7Nebe0o5BJiT5/S7ZnuZY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=CsLTmwDYUQuPdEGJ2URh4YYrVQjku/PYtQd8szB9HFBHKuxNiHG8jlkrL7gi1baJv baOlP721yc+Gapvn+co/bsCE+vzOe7wj38uGpYqZPkxomRAwIz0bQTUhRLhTAuqqra dcAYfgKFIupV+om73sgPaweqXIGMwkg5fWtKJMpvY7FG1n04OkQOJYThS8OWkrXRF/ 6d+zCI/PEFFnvI3TBktpF/UQ7XAfs6aQrSu5o0XLNpvLlz/KIh0d4q4F8mng6kmC35 gHgYzeK4HV1Zw3Tpumbe8aupeoEBK6jboDtDlQeHq19XetZJxR/N2esfUJW+ShNiZf qTij8AvQ7COkA== Date: Thu, 3 Sep 2026 12:22:45 +0300 From: Mike Rapoport To: Xueyuan Chen Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, usama.arif@linux.dev, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, kas@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 1/3] mm: make persistent huge zero folio read-only Message-ID: References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260901151818.3191443-2-xueyuan.chen21@gmail.com> On Tue, Sep 01, 2026 at 11:18:16PM +0800, Xueyuan Chen wrote: > The persistent huge zero folio is shared globally and should stay zero > after initialization. As Jann Horn pointed out [1], kernel bugs have > ended up writing to pages that were meant to be read-only, including in > security-sensitive cases. Making the folio read-only in the direct map > turns such writes into faults instead of silent zero-page corruption. > > Add a page-based helper consistent with the existing direct-map interfaces. > Handle TLB invalidation in the architecture implementation; unsupported > architectures retain their current behavior. > > Protect the folio after initialization. Skip highmem folios, which have no > permanent direct-map mapping. > > Inspired by Jann Horn's read-only zero page work [1] and follow-up > discussion [3] with Yang Shi. > > Link: https://lore.kernel.org/r/20260508-ro-zeropage-v1-1-9808abc20b49@google.com [1] > Link: https://lore.kernel.org/r/0e5b23a6-4895-454a-9dfa-6dc21adc2991@kernel.org [2] > Link: https://lore.kernel.org/r/CAHbLzkrXXe7r3n3jXgDKtwZhRqj=jDx9E6dLOULohnhBguvi9A@mail.gmail.com [3] > > Suggested-by: David Hildenbrand > Suggested-by: Usama Arif > Co-developed-by: Lance Yang > Signed-off-by: Lance Yang > Signed-off-by: Xueyuan Chen > --- > include/linux/set_memory.h | 17 +++++++++++++++++ > mm/huge_memory.c | 13 ++++++++++--- > 2 files changed, 27 insertions(+), 3 deletions(-) > > diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h > index 3fe293cfed8c..ed9ce04b18a1 100644 > --- a/include/linux/set_memory.h > +++ b/include/linux/set_memory.h > @@ -54,6 +54,23 @@ static inline bool can_set_direct_map(void) > #endif > #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ > > +#ifndef set_direct_map_ro > +/** > + * set_direct_map_ro - make a direct-map range read-only > + * @page: first page in the direct-map range > + * @nr: number of pages in the range > + * > + * Make the direct-map range starting at @page read-only and invalidate stale > + * writable translations before returning. > + * > + * Return: 0 on success, or a negative error code on failure. > + */ > +static inline int set_direct_map_ro(struct page *page, unsigned int nr) > +{ > + return 0; > +} > +#endif > + > #ifdef CONFIG_X86_64 > int set_mce_nospec(unsigned long pfn); > int clear_mce_nospec(unsigned long pfn); > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 54494c3fa983..742283b36d74 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -42,6 +42,7 @@ > #include > #include > #include > +#include > > #include > #include "internal.h" > @@ -291,10 +292,16 @@ static int __init huge_zero_init(void) > huge_zero_folio = alloc_huge_zero_folio(); > if (!huge_zero_folio) { > pr_warn("Allocating persistent huge zero folio failed\n"); > - } else { > - huge_zero_pfn = folio_pfn(huge_zero_folio); > - count_vm_event(THP_ZERO_PAGE_ALLOC); > + return 0; > } > + > + huge_zero_pfn = folio_pfn(huge_zero_folio); > + count_vm_event(THP_ZERO_PAGE_ALLOC); > + > + /* Highmem folios have no permanent direct-map mapping to protect. */ > + if (!folio_test_highmem(huge_zero_folio)) > + set_direct_map_ro(folio_page(huge_zero_folio, 0), HPAGE_PMD_NR); Sorry, I don't remember if it was discussed previously, but why can't we use the existing set_memory_ro() here? > + > return 0; > } > > -- > 2.47.3 > -- Sincerely yours, Mike.