From patchwork Wed Apr 30 11:07:47 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 886184 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3FE69248F77; Wed, 30 Apr 2025 11:26:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746012411; cv=none; b=iEwnlI/GcDKQ7pY/c5O28epAidwMQXrRgiWamcR1hLwL20BAn9OBeMDxZv0uwmY8A2WIdusLMCOWD47DpIGS/eTsb3XSkvnR2uZz6esuD41LHik4mi7hJbDG7iexA1j/Px7QQIocf94Z6zlhH+uXWUdXc0adC/+zn5d4UAAuc4s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746012411; c=relaxed/simple; bh=9+/BuRDGAA6TLDb0yk7rHBW8mHDlaavPQl2vlVEAVkI=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=khYqu/PxefYnawpXdg4WTkA971cWWv9IcRLPXQ0/o6QzTPy/LfgO6RnDOkNVwWUnIOtWO3TuQkj1UzTfJ66Te5TbB9xTOjfjC6ugl+xIxDu2QahRzBKdFNgoyU1ydVxwjFnX530H6+Q/QPIKebrO7ribaNEw2ggnfwvvZ3f/bas= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=W1jXDB8d; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="W1jXDB8d" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=k9Ri4ZyqEibe0HpDT575gbrV5ZF8Kp/wefhRDjxVdRo=; b=W1jXDB8dLl80ZTVasLrOzMMEzh nvwN1guUG/MrY2bLLuthDILrx8Ibgv6CJWPLpz5RouJhh1LnVsA7FH3OzBrgjDqTRwUj2A5NR+dfH A9gBoUxEFgokwWwbM3xdPmqE+z+MmF6/Kv/YCpNb7bFDbmbrRHrabmPPZZcEPOVPN5CxVhoCymmzG YeTmrD+7eYkUFrcEnXXOgSnHyTuoP2Mu/c7Cgl1K+uB0aBhA67topbnJgXxusnUvWIhICoNrA09QW wTNQxOmcrHWCvC1vEZgE7Yp5KlsVeBmCsfEcWSXh8+mTopS1HAcHUojp5AESrS5oivzW6qA6SnOTZ em/Kue3A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1uA5aH-0000000Dm7z-0HsX; Wed, 30 Apr 2025 11:26:37 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 024933085D7; Wed, 30 Apr 2025 13:26:36 +0200 (CEST) Message-ID: <20250430112350.443414861@infradead.org> User-Agent: quilt/0.66 Date: Wed, 30 Apr 2025 13:07:47 +0200 From: Peter Zijlstra To: x86@kernel.org Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, seanjc@google.com, pbonzini@redhat.com, ardb@kernel.org, kees@kernel.org, Arnd Bergmann , gregkh@linuxfoundation.org, jpoimboe@kernel.org, peterz@infradead.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, samitolvanen@google.com, ojeda@kernel.org Subject: [PATCH v2 13/13] objtool: Validate kCFI calls References: <20250430110734.392235199@infradead.org> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Validate that all indirect calls adhere to kCFI rules. Notably doing nocfi indirect call to a cfi function is broken. Apparently some Rust 'core' code violates this and explodes when ran with FineIBT. All the ANNOTATE_NOCFI_SYM sites are prime targets for attackers. - runtime EFI is especially henous because it also needs to disable IBT. Basically calling unknown code without CFI protection at runtime is a massice security issue. - Kexec image handover; if you can exploit this, you get to keep it :-) - KVM, for the interrupt injection calling IDT gates directly. Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/machine_kexec_64.c | 4 +++ arch/x86/kvm/vmx/vmenter.S | 5 ++++ arch/x86/platform/efi/efi_stub_64.S | 4 +++ drivers/misc/lkdtm/perms.c | 5 ++++ include/linux/objtool.h | 10 ++++++++ include/linux/objtool_types.h | 1 tools/include/linux/objtool_types.h | 1 tools/objtool/check.c | 41 ++++++++++++++++++++++++++++++++++++ tools/objtool/include/objtool/elf.h | 1 9 files changed, 72 insertions(+) --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -421,6 +421,10 @@ void __nocfi machine_kexec(struct kimage __ftrace_enabled_restore(save_ftrace_enabled); } +/* + * Handover to the next kernel, no CFI concern. + */ +ANNOTATE_NOCFI_SYM(machine_kexec); /* arch-dependent functionality related to kexec file-based syscall */ --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -363,5 +363,10 @@ SYM_FUNC_END(vmread_error_trampoline) .section .text, "ax" SYM_FUNC_START(vmx_do_interrupt_irqoff) + /* + * Calling an IDT gate directly; annotate away the CFI concern for now. + * Should be fixed if possible. + */ + ANNOTATE_NOCFI_SYM VMX_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1 SYM_FUNC_END(vmx_do_interrupt_irqoff) --- a/arch/x86/platform/efi/efi_stub_64.S +++ b/arch/x86/platform/efi/efi_stub_64.S @@ -11,6 +11,10 @@ #include SYM_FUNC_START(__efi_call) + /* + * The EFI code doesn't have any CFI, annotate away the CFI violation. + */ + ANNOTATE_NOCFI_SYM pushq %rbp movq %rsp, %rbp and $~0xf, %rsp --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include @@ -86,6 +87,10 @@ static noinline __nocfi void execute_loc func(); pr_err("FAIL: func returned\n"); } +/* + * Explicitly doing the wrong thing for testing. + */ +ANNOTATE_NOCFI_SYM(execute_location); static void execute_user_location(void *dst) { --- a/include/linux/objtool.h +++ b/include/linux/objtool.h @@ -184,6 +184,15 @@ * WARN using UD2. */ #define ANNOTATE_REACHABLE(label) __ASM_ANNOTATE(label, ANNOTYPE_REACHABLE) +/* + * This should not be used; it annotates away CFI violations. There are a few + * valid use cases like kexec handover to the next kernel image, and there is + * no security concern there. + * + * There are also a few real issues annotated away, like EFI because we can't + * control the EFI code. + */ +#define ANNOTATE_NOCFI_SYM(sym) asm(__ASM_ANNOTATE(sym, ANNOTYPE_NOCFI)) #else #define ANNOTATE_NOENDBR ANNOTATE type=ANNOTYPE_NOENDBR @@ -194,6 +203,7 @@ #define ANNOTATE_INTRA_FUNCTION_CALL ANNOTATE type=ANNOTYPE_INTRA_FUNCTION_CALL #define ANNOTATE_UNRET_BEGIN ANNOTATE type=ANNOTYPE_UNRET_BEGIN #define ANNOTATE_REACHABLE ANNOTATE type=ANNOTYPE_REACHABLE +#define ANNOTATE_NOCFI_SYM ANNOTATE type=ANNOTYPE_NOCFI #endif #if defined(CONFIG_NOINSTR_VALIDATION) && \ --- a/include/linux/objtool_types.h +++ b/include/linux/objtool_types.h @@ -65,5 +65,6 @@ struct unwind_hint { #define ANNOTYPE_IGNORE_ALTS 6 #define ANNOTYPE_INTRA_FUNCTION_CALL 7 #define ANNOTYPE_REACHABLE 8 +#define ANNOTYPE_NOCFI 9 #endif /* _LINUX_OBJTOOL_TYPES_H */ --- a/tools/include/linux/objtool_types.h +++ b/tools/include/linux/objtool_types.h @@ -65,5 +65,6 @@ struct unwind_hint { #define ANNOTYPE_IGNORE_ALTS 6 #define ANNOTYPE_INTRA_FUNCTION_CALL 7 #define ANNOTYPE_REACHABLE 8 +#define ANNOTYPE_NOCFI 9 #endif /* _LINUX_OBJTOOL_TYPES_H */ --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2388,6 +2388,8 @@ static int __annotate_ifc(struct objtool static int __annotate_late(struct objtool_file *file, int type, struct instruction *insn) { + struct symbol *sym; + switch (type) { case ANNOTYPE_NOENDBR: /* early */ @@ -2429,6 +2431,15 @@ static int __annotate_late(struct objtoo insn->dead_end = false; break; + case ANNOTYPE_NOCFI: + sym = insn->sym; + if (!sym) { + ERROR_INSN(insn, "dodgy NOCFI annotation"); + break; + } + insn->sym->nocfi = 1; + break; + default: ERROR_INSN(insn, "Unknown annotation type: %d", type); return -1; @@ -3998,6 +4009,36 @@ static int validate_retpoline(struct obj warnings++; } + if (!opts.cfi) + return warnings; + + /* + * kCFI call sites look like: + * + * movl $(-0x12345678), %r10d + * addl -4(%r11), %r10d + * jz 1f + * ud2 + * 1: cs call __x86_indirect_thunk_r11 + * + * Verify all indirect calls are kCFI adorned by checking for the + * UD2. Notably, doing __nocfi calls to regular (cfi) functions is + * broken. + */ + list_for_each_entry(insn, &file->retpoline_call_list, call_node) { + struct symbol *sym = insn->sym; + + if (sym && sym->type == STT_FUNC && !sym->nocfi) { + struct instruction *prev = + prev_insn_same_sym(file, insn); + + if (!prev || prev->type != INSN_BUG) { + WARN_INSN(insn, "no-cfi indirect call!"); + warnings++; + } + } + } + return warnings; } --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -70,6 +70,7 @@ struct symbol { u8 local_label : 1; u8 frame_pointer : 1; u8 ignore : 1; + u8 nocfi : 1; struct list_head pv_target; struct reloc *relocs; };