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 D953229BDBF; Wed, 1 Oct 2025 17:22:28 +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=1759339351; cv=none; b=UDatUE3XPWOlt3tUt8zyRB8r4KZhJlmftoQH/nTuyFYQhiQAUcvUw7AxMrZiUrkWlzxzrE0wVypprtXLtaeGD8sGOXmO2VixN4Bs8YBbLxsbFOrMJOAxSAvGIqD2Z+j8T+rbg+lIYhnXaEgTpDFySFEe45uCQGXt46V1dKDe0Aw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759339351; c=relaxed/simple; bh=KtHH5slsD8Ox5MoPLqaiqd9jBeTgdv0YVlgjsuTd720=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JeQ/hRdBhIQQ6iZ6RvF0jz2W7NGYip87U/gsbrm77z7tejO6zx5hicaCLyKpEYRrn1+QB9ZQLt4OKEkzUTKxloSWFhKycmZdstl1lPL4ww7512R2u3ICB4iU79jvM++mIYYv1Wl36uA1Vigug06opDDDeH6cgm72U2HneI284/o= 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; 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 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 DDF2116F8; Wed, 1 Oct 2025 10:22:19 -0700 (PDT) Received: from [10.57.66.40] (unknown [10.57.66.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 30AE33F59E; Wed, 1 Oct 2025 10:22:22 -0700 (PDT) Message-ID: <69b1c489-b4cb-4bee-aff1-6c76fc48cf29@arm.com> Date: Wed, 1 Oct 2025 19:22:20 +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: [RFC PATCH v5 13/18] mm: Map page tables with privileged pkey To: David Hildenbrand , linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Lorenzo Stoakes , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Rick Edgecombe , Ryan Roberts , Thomas Gleixner , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org References: <20250815085512.2182322-1-kevin.brodsky@arm.com> <20250815085512.2182322-14-kevin.brodsky@arm.com> <48ed62b1-cceb-4bce-923c-25c11dbccc37@redhat.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <48ed62b1-cceb-4bce-923c-25c11dbccc37@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 01/10/2025 17:28, David Hildenbrand wrote: > On 15.08.25 10:55, Kevin Brodsky wrote: > > Just wondering, should the patch subject be: > > "mm: protect page tables with privileged pkey" ? > > At least patch #2 tells me that set_memory_pkey() will set the > protection key, and the function is called > "kpkeys_protect_pgtable_memory"? > > Just trying to connect the dots here :) That's fair! I suppose I meant "map with privileged pkey" in the sense of "modify the mapping/PTE to set the pkey". But I see how that can be confusing, as we're not creating any mapping. I'll reword that in v6. > >> If CONFIG_KPKEYS_HARDENED_PGTABLES is enabled, map allocated page >> table pages using a privileged pkey (KPKEYS_PKEY_PGTABLES), so that >> page tables can only be written under guard(kpkeys_hardened_pgtables). >> >> This patch is a no-op if CONFIG_KPKEYS_HARDENED_PGTABLES is disabled >> (default). >> >> Signed-off-by: Kevin Brodsky >> --- >>   include/linux/mm.h | 4 ++++ >>   1 file changed, 4 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index d9371d992033..4880cb7a4cb9 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -34,6 +34,7 @@ >>   #include >>   #include >>   #include >> +#include >>     struct mempolicy; >>   struct anon_vma; >> @@ -2979,6 +2980,8 @@ static inline bool __pagetable_ctor(struct >> ptdesc *ptdesc) >>         __folio_set_pgtable(folio); >>       lruvec_stat_add_folio(folio, NR_PAGETABLE); >> +    if (kpkeys_protect_pgtable_memory(folio)) >> +        return false; >>       return true; >>   } >>   @@ -2989,6 +2992,7 @@ static inline void pagetable_dtor(struct >> ptdesc *ptdesc) >>       ptlock_free(ptdesc); >>       __folio_clear_pgtable(folio); >>       lruvec_stat_sub_folio(folio, NR_PAGETABLE); >> +    kpkeys_unprotect_pgtable_memory(folio); > > This is all rather nasty. Not your fault. > > In the near future page tables will not be folios, and the whole > ptdesc_folio() conversion will not make any sense. Ah, interesting. Any patches/series I should be aware of? > > Likely you should make kpkeys_protect_pgtable_memory() etc. consume an > address range, or a page range right from the start. Got it. That said, as per the discussion on the cover letter [1], it's quite likely that we'll have to change the approach completely anyway (i.e. allocate PTPs from a dedicated pool where the pkey is already set). - Kevin [1] lore.kernel.org/r/aMwd7IJVECEy8mzf@willie-the-truck