linux-kernel - Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9247436d-ae01-4eb8-bd5d-370b2fb2eebc@intel.com>
Date: Tue, 8 Apr 2025 09:54:42 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
 Andreas Larsson <andreas@...sler.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 "David S. Miller" <davem@...emloft.net>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Mark Rutland <mark.rutland@....com>, Michael Ellerman <mpe@...erman.id.au>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>, Palmer Dabbelt
 <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>,
 Peter Zijlstra <peterz@...radead.org>, Qi Zheng
 <zhengqi.arch@...edance.com>, Ryan Roberts <ryan.roberts@....com>,
 Will Deacon <will@...nel.org>, Yang Shi <yang@...amperecomputing.com>,
 linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-csky@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
 linux-openrisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free_kernel()

On 4/8/25 09:37, Matthew Wilcox wrote:
> On Tue, Apr 08, 2025 at 08:22:47AM -0700, Dave Hansen wrote:
>> Are there any tests for folio_test_pgtable() at free_page() time? If we
>> had that, it would make it less likely that another free_page() user
>> could sneak in without calling the destructor.
> It's hidden, but yes:
> 
> static inline bool page_expected_state(struct page *page,
>                                         unsigned long check_flags)
> {
>         if (unlikely(atomic_read(&page->_mapcount) != -1))
>                 return false;
> 
> PageTable uses page_type which aliases with mapcount, so this check
> covers "PageTable is still set when the last refcount to it is put".

Huh, so shouldn't we have ended up in bad_page() for these, other than:

        pagetable_dtor(virt_to_ptdesc(pmd));
        free_page((unsigned long)pmd);

?