From patchwork Tue Feb 14 20:52:36 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 9572865 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 3E62B60578 for ; Tue, 14 Feb 2017 20:55:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2C0E026C9B for ; Tue, 14 Feb 2017 20:55:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 20D042840E; Tue, 14 Feb 2017 20:55:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 28FBF26C9B for ; Tue, 14 Feb 2017 20:55:15 +0000 (UTC) Received: (qmail 25714 invoked by uid 550); 14 Feb 2017 20:55:08 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 24421 invoked from network); 14 Feb 2017 20:55:05 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=eWAkgvhAv3t7OpzPEj0QJOmV6jwfbQ98c8FjCO39BYE=; b=gJzbLwBhWdkpXezFhkmOSDZTtF/YhJWWA0wUkvxkceXKfGeK7nC83A3GbbJHGEeil7 z8C0+A91/ZEEJ2ARK9OuMdQGkG9Sssl9ecTVTxLfO3NpSDDKYmNfItNR4kjl8NXZfTfV nZ+ZicgC2jXwN6cG1q1amgrlTcdVIe/RQr740= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=eWAkgvhAv3t7OpzPEj0QJOmV6jwfbQ98c8FjCO39BYE=; b=dN9fU7bl3uXtbPA9AIJuZQ/ge0+68LiJ5O9ERjGEjMwkSEYrHHvSfOV+EDDLjT7H35 rXiFwJFRawZU0621q9rZg2dqQXPO/98KtiAGdZbWaTkO4ZDUZ9wof94HaC2JD4C406vV UnW5eW/AgNyzISLA/7tDzEUyblUBP1RWfEne8cDKI8jCMBnpcTJRE9T0n+IHxzlHURLA BYPDot6q1/Ulv8DjcXnYYN7xGoy4qJQUkVuhcrFd4tv6vF3RwVtJhxj0W3os4VGRcGcl 5Jngo8/EGIeT5DZFLtN7NCk+ChgVyavOQ6ebpY1coCPAh8qR1INxlZmGx/JTIh3/Hn4U v6GQ== X-Gm-Message-State: AMke39kQ4AoI/00gOf8PFbcVTVGthvt7JQpwpCJ1s7GzxbP8VHU0p13jWiaZ65Tv2Nb0EV+q X-Received: by 10.223.150.84 with SMTP id c20mr26205974wra.178.1487105694175; Tue, 14 Feb 2017 12:54:54 -0800 (PST) From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, labbott@fedoraproject.org Cc: kernel-hardening@lists.openwall.com, kvmarm@lists.cs.columbia.edu, marc.zyngier@arm.com, andre.przywara@arm.com, suzuki.poulose@arm.com, james.morse@arm.com, keescook@chromium.org, Ard Biesheuvel Date: Tue, 14 Feb 2017 20:52:36 +0000 Message-Id: <1487105558-21897-4-git-send-email-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1487105558-21897-1-git-send-email-ard.biesheuvel@linaro.org> References: <1487105558-21897-1-git-send-email-ard.biesheuvel@linaro.org> Subject: [kernel-hardening] [PATCH v3 3/5] arm64: alternatives: apply boot time fixups via the linear mapping X-Virus-Scanned: ClamAV using ClamSMTP One important rule of thumb when desiging a secure software system is that memory should never be writable and executable at the same time. We mostly adhere to this rule in the kernel, except at boot time, when regions may be mapped RWX until after we are done applying alternatives or making other one-off changes. For the alternative patching, we can improve the situation by applying the fixups via the linear mapping, which is never mapped with executable permissions. So map the linear alias of .text with RW- permissions initially, and remove the write permissions as soon as alternative patching has completed. Reviewed-by: Laura Abbott Reviewed-by: Mark Rutland Tested-by: Mark Rutland Signed-off-by: Ard Biesheuvel --- arch/arm64/include/asm/mmu.h | 1 + arch/arm64/kernel/alternative.c | 2 +- arch/arm64/kernel/smp.c | 1 + arch/arm64/mm/mmu.c | 22 +++++++++++++++----- 4 files changed, 20 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h index 47619411f0ff..5468c834b072 100644 --- a/arch/arm64/include/asm/mmu.h +++ b/arch/arm64/include/asm/mmu.h @@ -37,5 +37,6 @@ extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, unsigned long virt, phys_addr_t size, pgprot_t prot, bool page_mappings_only); extern void *fixmap_remap_fdt(phys_addr_t dt_phys); +extern void mark_linear_text_alias_ro(void); #endif diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index 06d650f61da7..8cee29d9bc07 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -128,7 +128,7 @@ static void __apply_alternatives(void *alt_region) for (i = 0; i < nr_inst; i++) { insn = get_alt_insn(alt, origptr + i, replptr + i); - *(origptr + i) = cpu_to_le32(insn); + ((u32 *)lm_alias(origptr))[i] = cpu_to_le32(insn); } flush_icache_range((uintptr_t)origptr, diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index a8ec5da530af..d6307e311a10 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -432,6 +432,7 @@ void __init smp_cpus_done(unsigned int max_cpus) setup_cpu_features(); hyp_mode_check(); apply_alternatives_all(); + mark_linear_text_alias_ro(); } void __init smp_prepare_boot_cpu(void) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index a98419b72a09..b7ce0b9ad096 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -398,16 +398,28 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end debug_pagealloc_enabled()); /* - * Map the linear alias of the [_text, __init_begin) interval as - * read-only/non-executable. This makes the contents of the - * region accessible to subsystems such as hibernate, but - * protects it from inadvertent modification or execution. + * Map the linear alias of the [_text, __init_begin) interval + * as non-executable now, and remove the write permission in + * mark_linear_text_alias_ro() below (which will be called after + * alternative patching has completed). This makes the contents + * of the region accessible to subsystems such as hibernate, + * but protects it from inadvertent modification or execution. */ __create_pgd_mapping(pgd, kernel_start, __phys_to_virt(kernel_start), - kernel_end - kernel_start, PAGE_KERNEL_RO, + kernel_end - kernel_start, PAGE_KERNEL, early_pgtable_alloc, debug_pagealloc_enabled()); } +void __init mark_linear_text_alias_ro(void) +{ + /* + * Remove the write permissions from the linear alias of .text/.rodata + */ + update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text), + (unsigned long)__init_begin - (unsigned long)_text, + PAGE_KERNEL_RO); +} + static void __init map_mem(pgd_t *pgd) { struct memblock_region *reg;