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Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wU06o-00000006RGl-1aVM for linux-arm-kernel@lists.infradead.org; Mon, 01 Jun 2026 10:43:04 +0000 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 2DF0B1516; Mon, 1 Jun 2026 03:42:55 -0700 (PDT) Received: from [10.57.94.8] (unknown [10.57.94.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CE8AB3F905; Mon, 1 Jun 2026 03:42:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1780310580; bh=Surtzdfsfons0Igc45K6QS/muGPLmDhB31E+s1aspA8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=L7vvyWyP5yYoDEKRDyQEcn+KUcyIZLm2/zPqf2mFWbJd8f5vtwRD9mJ+gjQLemSmG 61GJ7fElvuDmqzB0boUzsETOcCIg+LT5X96dfHbuAGeuIYJbp6tPCru3g6Uz1zZTsM dtan6SzPh6XJ40fqoV65vNcSw4ucQjj+39rNxGKw= Message-ID: <502eadae-089f-41cb-a871-9ad6b8169e0d@arm.com> Date: Mon, 1 Jun 2026 12:42:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 07/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , Jann Horn , linux-mm@kvack.org, linux-hardening@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org References: <20260529150150.1670604-17-ardb+git@google.com> <20260529150150.1670604-24-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260529150150.1670604-24-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260601_114303_033394_A152E774 X-CRM114-Status: GOOD ( 24.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 29/05/2026 17:01, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > Now that the map_mem() routines respect existing page mappings and > contiguous granule sized blocks with the contiguous bit cleared, there > is no longer a reason to play tricks with the memblock NOMAP attribute. > > Instead, the kfence pool can be allocated and mapped with page > granularity first, and this granularity will be respected when the rest > of DRAM is mapped later, even if block and contiguous mappings are > allowed for the remainder of those mappings. > > Add the NO_EXEC_MAPPINGS flag to ensure that hierarchical XN attributes > are set on the intermediate page tables that are allocated when mapping > the pool. > > Signed-off-by: Ard Biesheuvel Reviewed-by: Kevin Brodsky > --- > arch/arm64/mm/mmu.c | 27 +++++--------------- > 1 file changed, 6 insertions(+), 21 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index d7a6991e1844..cdf8b3510229 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1083,36 +1083,24 @@ static int __init parse_kfence_early_init(char *arg) > } > early_param("kfence.sample_interval", parse_kfence_early_init); > > -static phys_addr_t __init arm64_kfence_alloc_pool(void) > +static void __init arm64_kfence_map_pool(void) > { > phys_addr_t kfence_pool; > > if (!kfence_early_init) > - return 0; > + return; > > kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE); > if (!kfence_pool) { > pr_err("failed to allocate kfence pool\n"); > kfence_early_init = false; > - return 0; > - } > - > - /* Temporarily mark as NOMAP. */ > - memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE); > - > - return kfence_pool; > -} > - > -static void __init arm64_kfence_map_pool(phys_addr_t kfence_pool) > -{ > - if (!kfence_pool) > return; > + } > > /* KFENCE pool needs page-level mapping. */ > __map_memblock(kfence_pool, kfence_pool + KFENCE_POOL_SIZE, > pgprot_tagged(PAGE_KERNEL), > - NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); > - memblock_clear_nomap(kfence_pool, KFENCE_POOL_SIZE); > + NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS | NO_EXEC_MAPPINGS); > __kfence_pool = phys_to_virt(kfence_pool); > } > > @@ -1144,8 +1132,7 @@ bool arch_kfence_init_pool(void) > } > #else /* CONFIG_KFENCE */ > > -static inline phys_addr_t arm64_kfence_alloc_pool(void) { return 0; } > -static inline void arm64_kfence_map_pool(phys_addr_t kfence_pool) { } > +static inline void arm64_kfence_map_pool(void) { } > > #endif /* CONFIG_KFENCE */ > > @@ -1155,7 +1142,6 @@ static void __init map_mem(void) > phys_addr_t kernel_start = __pa_symbol(_text); > phys_addr_t kernel_end = __pa_symbol(__init_begin); > phys_addr_t start, end; > - phys_addr_t early_kfence_pool; > int flags = NO_EXEC_MAPPINGS; > u64 i; > > @@ -1172,7 +1158,7 @@ static void __init map_mem(void) > BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end) && > pgd_index(_PAGE_OFFSET(VA_BITS_MIN)) != PTRS_PER_PGD - 1); > > - early_kfence_pool = arm64_kfence_alloc_pool(); > + arm64_kfence_map_pool(); > > linear_map_requires_bbml2 = !force_pte_mapping() && can_set_direct_map(); > > @@ -1210,7 +1196,6 @@ static void __init map_mem(void) > */ > __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS); > memblock_clear_nomap(kernel_start, kernel_end - kernel_start); > - arm64_kfence_map_pool(early_kfence_pool); > } > > void mark_rodata_ro(void)