From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D725DC98318 for ; Fri, 25 Sep 2026 02:15:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=4NZMBuFlBSPtFWQr/+9V5+/tkqwiVb2mT8iCwcDe+8A=; b=Um+HIhh4HzDIMHHoQ3BGu3MrjJ 4ZtwSkwGn/JG5fsSrAoQatiPClf92kDCF/Y3l6KVEnBg9ZNoaU2BpJ3i8AEDLPybiE1FpVNBI78Vt W/ObKmLhYcP2HAE0/9R0T8FXrJA/lnrDfU8PG46FD1iS+RAR70NI8sKZ1RCJqAnd+Ffp5l5pHrkc2 bVwS8gJMvHQ8hb5Vh4HUG411ppMTTPqaiy6BtrC9itNXDZNb/vZnhIdY1jgA6xrPfNW6zUcXuGx0P b3cpEObH6JZF593/JwGZhiVKh1SfCOaraGkxKD382Gw4nkIthIWIr4tr6SIMStFrzM8a7iRvlKkod gQ6Cm/Pg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9vSh-0000000CX9W-1dsx; Fri, 25 Sep 2026 02:14:55 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9vSf-0000000CX9I-2YAc; Fri, 25 Sep 2026 02:14:53 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id C0CD640940; Fri, 25 Sep 2026 02:14:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A09A71F000FF; Fri, 25 Sep 2026 02:14:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790302492; bh=4NZMBuFlBSPtFWQr/+9V5+/tkqwiVb2mT8iCwcDe+8A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=RtZfvI+0S4V+OekP5WBn1nVIUqDPiXLFh3fdRqN8ZDUwVce/S4asXsblhu3wC7DOE GbAIh9/C07mr0GF0tbofTmf5Vh0QKmJfWlUDUQKZbx5gDAAcqcXWxm0sgLQc//ypHv jO9CmqTIYSTr9t9weTOjL/NCQbH2O/ONs0pTwsy/iCX3GdEjutOGBw8JIjznuZF3M5 L9mY4BtABZcPbuC7nChFNUEdrvwSCyUvTACaL1efLT9QKt6flCrcCxo6cKHwv7vxLo laFfSlVsH6bLZ+kmYF9DAgd+zE2yBn9b2RxyvFW9ozMp74Cn8CBLnSECJFK8Jp0Lj3 67LYDZ+gM9l5Q== Date: Thu, 24 Sep 2026 19:14:52 -0700 From: Kees Cook To: Ben Cressey Cc: Catalin Marinas , Will Deacon , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Pasha Tatashin , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Sami Tolvanen , David Woodhouse , kexec@lists.infradead.org, stable@vger.kernel.org Subject: Re: [PATCH] arm64: kexec: mark machine_kexec() __nocfi Message-ID: <202609241804.BB23BF10@keescook> References: <20260924-arm64-kexec-nocfi-v1-1-bbae2e2eadc8@cressey.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260924-arm64-kexec-nocfi-v1-1-bbae2e2eadc8@cressey.dev> 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 Thu, Sep 24, 2026 at 10:42:30PM +0000, Ben Cressey wrote: > With CONFIG_CFI=y the kCFI check on this call loads a type hash from > kern_reloc - 4. arm64_relocate_new_kernel is SYM_CODE_START and carries > no hash. Its copy also sits at the start of the control page, which is > all that TTBR0 maps at this point, so the load faults and the kernel > oopses after "Bye!" instead of entering the new kernel: > [...] > arm64_relocate_new_kernel cannot be given a type hash, since the linker > script asserts that the relocation code starts at that symbol and a > hash would have to precede it. Mark machine_kexec() __nocfi instead, as > commit e2f8216ca2d8 ("arm64: Set __nocfi on swsusp_arch_resume()") did > for the same pattern on the hibernate path and commit 2114796ca041 > ("x86/kexec: Mark machine_kexec() with __nocfi") did on x86. I think e2f8216ca2d8 made a mistake here; using SYM_TYPED_FUNC_START wouldn't have been tautological: the defense is making sure that the indirect call itself can't be used with a bad pointer. Fixing this correctly isn't so bad: it just needs to decouple the entrypoint from the page address. But, barring that, what I don't like here (and with x86) is that it covers the entire function, so _all_ indirect calls go unprotected. Can you pull the call out into an inline helper so that the other indirect call (cpu_soft_restart) doesn't lose coverage? -Kees P.S. Doing the whole SYM_TYPED_FUNC_START change (below, only build tested) is larger, but maybe things besides KCFI will want things before the entry point? arch/arm64/include/asm/kexec.h | 2 ++ arch/arm64/kernel/machine_kexec.c | 13 +++++++++++-- arch/arm64/kernel/relocate_kernel.S | 14 +++++++++----- arch/arm64/kernel/vmlinux.lds.S | 5 +++-- 4 files changed, 25 insertions(+), 9 deletions(-) diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h index 892e5bebda957..0be042ec22c1f 100644 --- a/arch/arm64/include/asm/kexec.h +++ b/arch/arm64/include/asm/kexec.h @@ -100,6 +100,8 @@ void cpu_soft_restart(unsigned long el2_switch, unsigned long entry, unsigned long arg0, unsigned long arg1, unsigned long arg2); +void arm64_relocate_new_kernel(struct kimage *kimage); + int machine_kexec_post_load(struct kimage *image); #define machine_kexec_post_load machine_kexec_post_load #endif diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c index 8f9bc2327dc85..1cf4cb135ee2b 100644 --- a/arch/arm64/kernel/machine_kexec.c +++ b/arch/arm64/kernel/machine_kexec.c @@ -136,9 +136,18 @@ int machine_kexec_post_load(struct kimage *kimage) kimage->arch.ttbr1 = __pa(trans_pgd); kimage->arch.zero_page = __pa_symbol(empty_zero_page); + /* + * The whole .kexec_relocate.text section is copied to the control + * page, but arm64_relocate_new_kernel is not required to be the first + * thing in it. Allow for whatever precedes it (e.g. a landing pad, + * a kCFI type hash, etc) by carrying its offset within the section + * across the copy. + */ reloc_size = __relocate_new_kernel_end - __relocate_new_kernel_start; memcpy(reloc_code, __relocate_new_kernel_start, reloc_size); - kimage->arch.kern_reloc = __pa(reloc_code); + kimage->arch.kern_reloc = __pa(reloc_code) + + ((unsigned long)arm64_relocate_new_kernel - + (unsigned long)__relocate_new_kernel_start); rc = trans_pgd_idmap_page(&info, &kimage->arch.ttbr0, &kimage->arch.t0sz, reloc_code); if (rc) diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index af1d720209764..81540c09a3db8 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -432,6 +432,7 @@ ASSERT(swapper_pg_dir - tramp_pg_dir == TRAMP_SWAPPER_OFFSET, ASSERT(__relocate_new_kernel_end - __relocate_new_kernel_start <= SZ_4K, "kexec relocation code is bigger than 4 KiB") ASSERT(KEXEC_CONTROL_PAGE_SIZE >= SZ_4K, "KEXEC_CONTROL_PAGE_SIZE is broken") -ASSERT(__relocate_new_kernel_start == arm64_relocate_new_kernel, - "kexec control page does not start with arm64_relocate_new_kernel") +ASSERT(arm64_relocate_new_kernel >= __relocate_new_kernel_start && + arm64_relocate_new_kernel < __relocate_new_kernel_end, + "kexec relocation entry point is outside the copied region") #endif diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c index 1cf4cb135ee2b..90302efebb426 100644 --- a/arch/arm64/kernel/machine_kexec.c +++ b/arch/arm64/kernel/machine_kexec.c @@ -202,7 +202,7 @@ void machine_kexec(struct kimage *kimage) restart(is_hyp_nvhe(), kimage->start, kimage->arch.dtb_mem, 0, 0); } else { - void (*kernel_reloc)(struct kimage *kimage); + typeof(arm64_relocate_new_kernel) *kernel_reloc; if (is_hyp_nvhe()) __hyp_set_vectors(kimage->arch.el2_vectors); diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S index 6cb4209f5dab5..e3e575c57fe12 100644 --- a/arch/arm64/kernel/relocate_kernel.S +++ b/arch/arm64/kernel/relocate_kernel.S @@ -8,6 +8,7 @@ * Pasha Tatashin */ +#include #include #include @@ -32,11 +33,14 @@ * new image to its final location. To assure that the * arm64_relocate_new_kernel routine which does that copy is not overwritten, * all code and data needed by arm64_relocate_new_kernel must be between the - * symbols arm64_relocate_new_kernel and arm64_relocate_new_kernel_end. The - * machine_kexec() routine will copy arm64_relocate_new_kernel to the kexec - * safe memory that has been set up to be preserved during the copy operation. + * symbols __relocate_new_kernel_start and __relocate_new_kernel_end. The + * machine_kexec() routine will copy that whole region to the kexec safe + * memory that has been set up to be preserved during the copy operation, + * and enter it at arm64_relocate_new_kernel's offset within it. + * + * It is called indirectly, through the copy, so it needs a kCFI type hash. */ -SYM_CODE_START(arm64_relocate_new_kernel) +SYM_TYPED_FUNC_START(arm64_relocate_new_kernel) /* * The kimage structure isn't allocated specially and may be clobbered * during relocation. We must load any values we need from it prior to @@ -98,4 +102,4 @@ SYM_CODE_START(arm64_relocate_new_kernel) mov x2, xzr mov x3, xzr br x28 /* Jumps from el1 */ -SYM_CODE_END(arm64_relocate_new_kernel) +SYM_FUNC_END(arm64_relocate_new_kernel) -- Kees Cook