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Fri, 20 Mar 2026 08:00:05 -0700 (PDT) Date: Fri, 20 Mar 2026 15:59:42 +0100 In-Reply-To: <20260320145934.2349881-15-ardb+git@google.com> Mime-Version: 1.0 References: <20260320145934.2349881-15-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=1198; i=ardb@kernel.org; h=from:subject; bh=dhCmT0xhgO1wynakhoxtMTULOKMtch1e7OuwxF75oGw=; b=owGbwMvMwCVmkMcZplerG8N4Wi2JIXNvwoMI8+i12Utr1y67d7vnI7fbJp4TO31Wf/7f9fSZp X3oO/cfHaUsDGJcDLJiiiwCs/++23l6olSt8yxZmDmsTCBDGLg4BWAigkyMDGscNhv8F7vWM/FC Br+T9vd3Pc+uP/MPefnRf/d5MatA3WeMDPcY8y/NOCEmXsvdHe7z5c29JU1ceyKN9p2IN9+S579 /KTsA X-Mailer: git-send-email 2.53.0.959.g497ff81fa9-goog Message-ID: <20260320145934.2349881-22-ardb+git@google.com> Subject: [PATCH v3 07/13] arm64: mm: Use hierarchical XN mapping for the fixmap From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260320_080008_348156_D5EE8D96 X-CRM114-Status: GOOD ( 12.60 ) 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 From: Ard Biesheuvel Nothing in the fixmap or in its vicinity requires executable permissions, and given that it is placed at exactly 1 GiB from the end of the virtual address space, we can safely set the hierarchical XN attributes on the level 2 table entries covering the fixmap, without running the risk of inadvertently taking away the executable permissions on an adjacent mappings. This is a hardening measure that reduces the risk of the fixmap being abused to create executable mappings in the kernel address space. Signed-off-by: Ard Biesheuvel --- arch/arm64/mm/fixmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c index c5c5425791da..c3dd3c868cf5 100644 --- a/arch/arm64/mm/fixmap.c +++ b/arch/arm64/mm/fixmap.c @@ -48,7 +48,8 @@ static void __init early_fixmap_init_pte(pmd_t *pmdp, unsigned long addr) if (pmd_none(pmd)) { ptep = bm_pte[BM_PTE_TABLE_IDX(addr)]; __pmd_populate(pmdp, __pa_symbol(ptep), - PMD_TYPE_TABLE | PMD_TABLE_AF); + PMD_TYPE_TABLE | PMD_TABLE_AF | + PMD_TABLE_PXN | PMD_TABLE_UXN); } } -- 2.53.0.959.g497ff81fa9-goog