linux-kernel - Re: [RFC PATCH v5 11/18] mm: Introduce kpkeys_hardened

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Message-ID: <c1226873-c790-49bd-876d-4539f95b4caf@arm.com>
Date: Mon, 1 Dec 2025 10:19:41 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski
 <luto@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 David Hildenbrand <david@...hat.com>, Ira Weiny <ira.weiny@...el.com>,
 Jann Horn <jannh@...gle.com>, Jeff Xu <jeffxu@...omium.org>,
 Joey Gouly <joey.gouly@....com>, Kees Cook <kees@...nel.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Marc Zyngier <maz@...nel.org>,
 Mark Brown <broonie@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 Maxwell Bland <mbland@...orola.com>, "Mike Rapoport (IBM)"
 <rppt@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Pierre Langlois <pierre.langlois@....com>,
 Quentin Perret <qperret@...gle.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Ryan Roberts <ryan.roberts@....com>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [RFC PATCH v5 11/18] mm: Introduce kpkeys_hardened_pgtables

On 28/11/2025 17:44, Yeoreum Yun wrote:
>> +int kpkeys_protect_pgtable_memory(struct folio *folio)
>> +{
>> +	unsigned long addr = (unsigned long)folio_address(folio);
> I think it might need to use untagged_addr()?

I've never seen untagged_addr() used on folio_address()/page_address()
(see for instance set_direct_map_valid_noflush() and
__kernel_map_pages() in arch/arm64/mm/pageattr.c).

It does seem that page_to_virt() sets the tag if KASAN is enabled
though... I'm not sure what to think, is there a wider issue here? We
might just be lucky and the sort of pages that these functions are
called on don't have their KASAN tag set.

- Kevin