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[79.224.240.123]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b7e898b99sm49008435e9.19.2025.08.29.12.13.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 Aug 2025 12:13:06 -0700 (PDT) Message-ID: Date: Fri, 29 Aug 2025 21:13:04 +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 v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature To: Kees Cook , Kevin Brodsky Cc: Ard Biesheuvel , Ryan Roberts , Mark Rutland , Catalin Marinas , Will Deacon , Anshuman Khandual , Oliver Upton , Yue Haibing , Marc Zyngier , Mark Brown , Andrew Morton , linux-arm-kernel@lists.infradead.org, Joey Gouly , Shameer Kolothum , Yeoreum Yun , James Morse , Hardevsinh Palaniya , Zhenhua Huang , Lorenzo Stoakes , Dev Jain , Yicong Yang , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org References: <20250829190721.it.373-kees@kernel.org> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29.08.25 21:07, Kees Cook wrote: > Seen during KPTI initialization: > > CFI failure at create_kpti_ng_temp_pgd+0x124/0xce8 (target: kpti_ng_pgd_alloc+0x0/0x14; expected type: 0xd61b88b6) > > The call site is alloc_init_pud() at arch/arm64/mm/mmu.c: > > pud_phys = pgtable_alloc(TABLE_PUD); > > alloc_init_pud() has the prototype: > > static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end, > phys_addr_t phys, pgprot_t prot, > phys_addr_t (*pgtable_alloc)(enum pgtable_type), > int flags) > > where the pgtable_alloc() prototype is declared. > > The target (kpti_ng_pgd_alloc) is used in arch/arm64/kernel/cpufeature.c: > > create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc), KPTI_NG_TEMP_VA, > PAGE_SIZE, PAGE_KERNEL, kpti_ng_pgd_alloc, 0); > > which is an alias for __create_pgd_mapping_locked() with prototype: > > extern __alias(__create_pgd_mapping_locked) > void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, > unsigned long virt, > phys_addr_t size, pgprot_t prot, > phys_addr_t (*pgtable_alloc)(enum pgtable_type), > int flags); > > __create_pgd_mapping_locked() passes the function pointer down: > > __create_pgd_mapping_locked() -> alloc_init_p4d() -> alloc_init_pud() > > But the target function (kpti_ng_pgd_alloc) has the wrong signature: > > static phys_addr_t __init kpti_ng_pgd_alloc(int shift); > > The "int" should be "enum pgtable_type". > > To make "enum pgtable_type" available to cpufeature.c, move > enum pgtable_type definition from arch/arm64/mm/mmu.c to > arch/arm64/include/asm/mmu.h. > > Adjust kpti_ng_pgd_alloc to use "enum pgtable_type" instead of "int". > The function behavior remains identical (parameter is unused). > > Fixes: c64f46ee1377 ("arm64: mm: use enum to identify pgtable level instead of *_SHIFT") > Signed-off-by: Kees Cook > --- > v2: Fixed the Fixes line. ;) > v1: https://lore.kernel.org/lkml/20250829154913.work.943-kees@kernel.org/ > Cc: Kevin Brodsky > Cc: Ard Biesheuvel > Cc: Ryan Roberts > Cc: Mark Rutland > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Anshuman Khandual > Cc: Oliver Upton > Cc: Yue Haibing > Cc: Marc Zyngier > Cc: Mark Brown > Cc: Andrew Morton > Cc: > --- > arch/arm64/include/asm/mmu.h | 7 +++++++ > arch/arm64/kernel/cpufeature.c | 5 +++-- > arch/arm64/mm/mmu.c | 7 ------- > 3 files changed, 10 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h > index 6e8aa8e72601..49f1a810df16 100644 > --- a/arch/arm64/include/asm/mmu.h > +++ b/arch/arm64/include/asm/mmu.h > @@ -17,6 +17,13 @@ > #include > #include > > +enum pgtable_type { > + TABLE_PTE, > + TABLE_PMD, > + TABLE_PUD, > + TABLE_P4D, > +}; Just noting that we now have "enum pgtable_level" in include/linux/pgtable.h that could at some point possibly be used here instead (not in this fix). -- Cheers David / dhildenb