From patchwork Mon Apr 14 11:11:46 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 14050241 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 0189229617A; Mon, 14 Apr 2025 11:39:36 +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=1744630778; cv=none; b=qwuGcuS/DithplOVFrFflDi8XFg80+np3+DAn/cYZY6kFO0zwwyOnm8J16V9DqRHg+0FCCumcGeEsFp5mH6wYzq6Vc01Hw6kDmIz9Vz/xMLsEcOEk89izkrYHb3CVB7BqLKmQxB8/VQpO9J5FdeyuWNVHV+5VCYKU+mpO9haLo4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744630778; c=relaxed/simple; bh=Ts6M3uwmEcf0nxVZByaZFCjJeVdYaGTB4wLygRG7khM=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=rpBJep/UqymQFU6SnqHHjzYwmpWXOzwSwtrw1LNC2Y90nGIFCUL32WenqWoB4M+65tuvG6G+cUQQgRel6LnHp/o315pLa38reUnWnnLnvLLj092hIo92PBy8x0uYRbO/L7esvRksuI/wLBE2maHZOhbO0oJAdt39AZ/0o1caqt8= 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=dqtW97mt; 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="dqtW97mt" 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=NERy+dpirG5HXq/uyAPT5n83ufEh61Nz/XhqyMRTQq8=; b=dqtW97mtT/lmt6C1tXpzMlETw/ kos6YrHRd2KrTgLrTVZ5SPLkxhYKrjcWkWPg+FA65gI3f2+naEbc+tr2cE0eNRfxrLoOI3RjENr75 NkqDwCajFKFMsbwUUWvSo8SdK31vNvE+evayPoZLpwcecT1zb0HnouolDsyPveD+bNd9EhiHYHZyC lL9RqZzkW41w621SQXZqxeGpm9FimJ4/Mif1k76tU9YYM/ku35qrMc4ZMPJ+7CZcOfVG3b7FrxfMO pBNUxlCreyu3dbIBOYGJxUniyBOaEx2Fw/U4ITiuh8u40hFRoRiCydZw/mrypKDVmVucL5wzB5ENP X1TH9zAQ==; 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 1u4I9v-00000009fKj-2kkF; Mon, 14 Apr 2025 11:39:27 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 37BC330119C; Mon, 14 Apr 2025 13:39:26 +0200 (CEST) Message-ID: <20250414113754.540779611@infradead.org> User-Agent: quilt/0.66 Date: Mon, 14 Apr 2025 13:11:46 +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, peterz@infradead.org, jpoimboe@kernel.org, pawan.kumar.gupta@linux.intel.com, seanjc@google.com, pbonzini@redhat.com, ardb@kernel.org, kees@kernel.org, Arnd Bergmann , gregkh@linuxfoundation.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 6/6] objtool: Validate kCFI calls References: <20250414111140.586315004@infradead.org> Precedence: bulk X-Mailing-List: kvm@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 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, once for the interrupt injection calling IDT gates directly. - KVM, once for the FASTOP emulation stuff. Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/machine_kexec_64.c | 1 arch/x86/kvm/emulate.c | 4 +++ arch/x86/kvm/vmx/vmenter.S | 4 +++ arch/x86/platform/efi/efi_stub_64.S | 4 +++ drivers/misc/lkdtm/perms.c | 2 + include/linux/objtool.h | 3 ++ 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 10 files changed, 62 insertions(+) --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -442,6 +442,7 @@ void __nocfi machine_kexec(struct kimage __ftrace_enabled_restore(save_ftrace_enabled); } +ANNOTATE_NOCFI_SYM(machine_kexec); /* arch-dependent functionality related to kexec file-based syscall */ --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5071,6 +5071,10 @@ static noinline int fastop(struct x86_em return emulate_de(ctxt); return X86EMUL_CONTINUE; } +/* + * The ASM stubs don't have CFI on. + */ +ANNOTATE_NOCFI_SYM(fastop); void init_decode_cache(struct x86_emulate_ctxt *ctxt) { --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -363,5 +363,9 @@ SYM_FUNC_END(vmread_error_trampoline) .section .text, "ax" SYM_FUNC_START(vmx_do_interrupt_irqoff) + /* + * Calling an IDT gate directly. + */ + ANNOTATE_NOCFI 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_NOCFI 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 +87,7 @@ static noinline __nocfi void execute_loc func(); pr_err("FAIL: func returned\n"); } +ANNOTATE_NOCFI_SYM(execute_location); static void execute_user_location(void *dst) { --- a/include/linux/objtool.h +++ b/include/linux/objtool.h @@ -185,6 +185,8 @@ */ #define ANNOTATE_REACHABLE(label) __ASM_ANNOTATE(label, ANNOTYPE_REACHABLE) +#define ANNOTATE_NOCFI_SYM(sym) asm(__ASM_ANNOTATE(sym, ANNOTYPE_NOCFI)) + #else #define ANNOTATE_NOENDBR ANNOTATE type=ANNOTYPE_NOENDBR #define ANNOTATE_RETPOLINE_SAFE ANNOTATE type=ANNOTYPE_RETPOLINE_SAFE @@ -194,6 +196,7 @@ #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 ANNOTATE type=ANNOTYPE_NOCFI #endif #if defined(CONFIG_NOINSTR_VALIDATION) && \ --- a/include/linux/objtool_types.h +++ b/include/linux/objtool_types.h @@ -66,5 +66,6 @@ struct unwind_hint { #define ANNOTYPE_INTRA_FUNCTION_CALL 7 #define ANNOTYPE_REACHABLE 8 #define ANNOTYPE_JUMP_TABLE 9 +#define ANNOTYPE_NOCFI 10 #endif /* _LINUX_OBJTOOL_TYPES_H */ --- a/tools/include/linux/objtool_types.h +++ b/tools/include/linux/objtool_types.h @@ -66,5 +66,6 @@ struct unwind_hint { #define ANNOTYPE_INTRA_FUNCTION_CALL 7 #define ANNOTYPE_REACHABLE 8 #define ANNOTYPE_JUMP_TABLE 9 +#define ANNOTYPE_NOCFI 10 #endif /* _LINUX_OBJTOOL_TYPES_H */ --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2387,6 +2387,8 @@ 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 */ @@ -2436,6 +2438,15 @@ static int __annotate_late(struct objtoo insn->_jump_table = (void *)1; break; + case ANNOTYPE_NOCFI: + sym = insn->sym; + if (!sym) { + WARN_INSN(insn, "dodgy NOCFI annotation"); + break; + } + insn->sym->nocfi = 1; + break; + default: ERROR_INSN(insn, "Unknown annotation type: %d", type); return -1; @@ -4006,6 +4017,36 @@ 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; };