From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752383AbeEPDat (ORCPT ); Tue, 15 May 2018 23:30:49 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:51588 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752172AbeEPDas (ORCPT ); Tue, 15 May 2018 23:30:48 -0400 Date: Tue, 15 May 2018 22:30:44 -0500 From: Josh Poimboeuf To: Linus Torvalds Cc: Alexey Dobriyan , Peter Anvin , kernel test robot , Ingo Molnar , Thomas Gleixner , Andrew Lutomirski , Borislav Petkov , Brian Gerst , Denys Vlasenko , Peter Zijlstra , Linux Kernel Mailing List , Peter Anvin , tipbuild@zytor.com, LKP Subject: Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##] Message-ID: <20180516033044.odb74pdgcn5nacwb@treble> References: <20180515080033.GA7714@yexl-desktop> <20180515210757.GA12225@avx2> <20180515214337.GA18021@avx2> <20180515222211.ods5hzne46hozojq@treble> <20180515224354.zmygmsnlqj5lrdbo@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 15, 2018 at 04:05:33PM -0700, Linus Torvalds wrote: > I wonder if there's some way to add a test for "ENTRY only works in a code > section"? I suppose we could add a discardable annotation to the ENTRY macro and have objtool validate that it's in a text section. I'm not sure whether it's worth it, but I could do it if you think it's a good idea. Below is a tentative objtool patch which catches asm code falling through to INT3 padding, though objtool is 64-bit only so there won't be any 32-bit coverage. It found zero hits on my config. I'll clean it up and submit it tomorrow-ish. diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 8344dd2f310a..3ed8cec6e765 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -285,11 +285,9 @@ ENTRY(early_idt_handler_array) .endif pushq $i # 72(%rsp) Vector number jmp early_idt_handler_common - UNWIND_HINT_IRET_REGS i = i + 1 .fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc .endr - UNWIND_HINT_IRET_REGS offset=16 END(early_idt_handler_array) early_idt_handler_common: diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h index b0d7dc3d71b5..6eb058a8ac00 100644 --- a/tools/objtool/arch.h +++ b/tools/objtool/arch.h @@ -33,7 +33,8 @@ #define INSN_STACK 8 #define INSN_BUG 9 #define INSN_NOP 10 -#define INSN_OTHER 11 +#define INSN_PADDING 11 +#define INSN_OTHER 12 #define INSN_LAST INSN_OTHER enum op_dest_type { diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c index 7e86a743f851..82b41bb93c02 100644 --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -421,7 +421,7 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, case 0xcc: /* int3: used for asm function padding by the __ALIGN macro */ - *type = INSN_NOP; + *type = INSN_PADDING; break; case 0xe3: diff --git a/tools/objtool/check.c b/tools/objtool/check.c index f4bbce838433..8a83a0d1693a 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1936,6 +1936,14 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, } return 0; + case INSN_PADDING: + if (!func) { + WARN_FUNC("code falls through to INT3 padding", + insn->sec, insn->offset); + return 1; + } + break; + case INSN_STACK: if (update_insn_state(insn, &state)) return 1; @@ -2032,7 +2040,8 @@ static bool ignore_unreachable_insn(struct instruction *insn) { int i; - if (insn->ignore || insn->type == INSN_NOP) + if (insn->ignore || insn->type == INSN_NOP || + insn->type == INSN_PADDING) return true; /*