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 X-Spam-Level: X-Spam-Status: No, score=-9.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32DD9C43331 for ; Thu, 2 Apr 2020 08:18:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F07832078E for ; Thu, 2 Apr 2020 08:18:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="nBGZpTRS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387809AbgDBISo (ORCPT ); Thu, 2 Apr 2020 04:18:44 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:35616 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387734AbgDBISl (ORCPT ); Thu, 2 Apr 2020 04:18:41 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0328HjjJ077967; Thu, 2 Apr 2020 08:18:18 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references; s=corp-2020-01-29; bh=+CAtcy/f3IIj1PBaeskCQni6ngQ5C9bOP5dthTyU7ME=; b=nBGZpTRSfA2lCjjEuMTwLdI5K4HcrKx9lmdjC0thRgtbwOx7OxMJ5WQkxEtW2THbib/N wAdhNk9Or0oMUv6Y9c0Uk7Jb/5FW8FRaMKbVLjSByZ5LsZcppjCZuM1MEkp2OeJwzQ9y ByE1brpFyzpgDzmum06zNxUaL2wgRn9oGWRKiefBd678zA3SB/B70s3jTVpsbt+YrnKA A6Mr3CjLAAK6TgK77wKVaJNk/dWphDx2NI9dQEhzIiw6IV1s5zSBgkZUZFSr+rnsoQAd DqNdPmdIYwemvCSsr7GcDqCf5th+hsoJaqlpZL6JtqxSp/KLOlbjlD7kjS6vbzOIaJWn Dw== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by userp2130.oracle.com with ESMTP id 303cev9u7f-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 02 Apr 2020 08:18:18 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0328H8nU126379; Thu, 2 Apr 2020 08:18:18 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 304sjnssr3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 02 Apr 2020 08:18:17 +0000 Received: from abhmp0011.oracle.com (abhmp0011.oracle.com [141.146.116.17]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 0328IHie003430; Thu, 2 Apr 2020 08:18:17 GMT Received: from linux-1.home (/92.157.90.160) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 02 Apr 2020 01:18:17 -0700 From: Alexandre Chartre To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, jpoimboe@redhat.com, peterz@infradead.org, jthierry@redhat.com, tglx@linutronix.de, alexandre.chartre@oracle.com Subject: [PATCH 4/7] objtool: Add support for return trampoline call Date: Thu, 2 Apr 2020 10:22:17 +0200 Message-Id: <20200402082220.808-5-alexandre.chartre@oracle.com> X-Mailer: git-send-email 2.18.2 In-Reply-To: <20200402082220.808-1-alexandre.chartre@oracle.com> References: <20200402082220.808-1-alexandre.chartre@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9578 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 adultscore=0 mlxscore=0 malwarescore=0 phishscore=0 suspectscore=1 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004020075 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9578 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 adultscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 spamscore=0 malwarescore=0 suspectscore=1 mlxscore=0 impostorscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004020075 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With retpoline, the return instruction is used to branch to an address stored on the stack. So, unlike a regular return instruction, when a retpoline return instruction is reached the stack has been modified compared to what we have when the function was entered. Provide the mechanism to explicitly call-out such return instruction so that objtool can correctly handle them. Signed-off-by: Alexandre Chartre --- tools/objtool/check.c | 78 +++++++++++++++++++++++++++++++++++++++++-- tools/objtool/check.h | 1 + 2 files changed, 76 insertions(+), 3 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 0cec91291d46..ed8e3ea1d8da 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1344,6 +1344,48 @@ static int read_intra_function_call(struct objtool_file *file) return 0; } +static int read_retpoline_ret(struct objtool_file *file) +{ + struct section *sec; + struct instruction *insn; + struct rela *rela; + + sec = find_section_by_name(file->elf, ".rela.discard.retpoline_ret"); + if (!sec) + return 0; + + list_for_each_entry(rela, &sec->rela_list, list) { + if (rela->sym->type != STT_SECTION) { + WARN("unexpected relocation symbol type in %s", + sec->name); + return -1; + } + + insn = find_insn(file, rela->sym->sec, rela->addend); + if (!insn) { + WARN("bad .discard.retpoline_ret entry"); + return -1; + } + + if (insn->type != INSN_RETURN) { + WARN_FUNC("retpoline_ret not a return", + insn->sec, insn->offset); + return -1; + } + + insn->retpoline_ret = true; + /* + * For the impact on the stack, make a return trampoline + * behaves like a pop of the return address. + */ + insn->stack_op.src.type = OP_SRC_POP; + insn->stack_op.dest.type = OP_DEST_REG; + insn->stack_op.dest.reg = CFI_RA; + } + + return 0; +} + static void mark_rodata(struct objtool_file *file) { struct section *sec; @@ -1403,6 +1445,10 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret; + ret = read_retpoline_ret(file); + if (ret) + return ret; + ret = add_call_destinations(file); if (ret) return ret; @@ -1432,7 +1478,8 @@ static bool is_fentry_call(struct instruction *insn) return false; } -static bool has_modified_stack_frame(struct insn_state *state) +static bool has_modified_stack_frame(struct insn_state *state, + bool check_registers) { int i; @@ -1442,6 +1489,9 @@ static bool has_modified_stack_frame(struct insn_state *state) state->drap) return true; + if (!check_registers) + return false; + for (i = 0; i < CFI_NUM_REGS; i++) if (state->regs[i].base != initial_func_cfi.regs[i].base || state->regs[i].offset != initial_func_cfi.regs[i].offset) @@ -1987,7 +2037,7 @@ static int validate_call(struct instruction *insn, struct insn_state *state) static int validate_sibling_call(struct instruction *insn, struct insn_state *state) { - if (has_modified_stack_frame(state)) { + if (has_modified_stack_frame(state, true)) { WARN_FUNC("sibling call from callable instruction with modified stack frame", insn->sec, insn->offset); return 1; @@ -2009,6 +2059,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, struct alternative *alt; struct instruction *insn, *next_insn; struct section *sec; + bool check_registers; u8 visited; int ret; @@ -2130,7 +2181,28 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, return 1; } - if (func && has_modified_stack_frame(&state)) { + /* + * With retpoline, the return instruction is used + * to branch to an address stored on the stack. + * So when we reach the ret instruction, the stack + * frame has been modified with the address to + * branch to and we need update the stack state. + * + * The retpoline address to branch to is typically + * pushed on the stack from a register, but this + * confuses the logic which checks callee saved + * registers. So we don't check if registers have + * been modified if we have a return trampoline. + */ + if (insn->retpoline_ret) { + update_insn_state(insn, &state); + check_registers = false; + } else { + check_registers = true; + } + + if (func && has_modified_stack_frame(&state, + check_registers)) { WARN_FUNC("return with modified stack frame", sec, insn->offset); return 1; diff --git a/tools/objtool/check.h b/tools/objtool/check.h index 2bd6d2f46baa..5ecd16ad71a8 100644 --- a/tools/objtool/check.h +++ b/tools/objtool/check.h @@ -37,6 +37,7 @@ struct instruction { bool dead_end, ignore, hint, save, restore, ignore_alts; bool intra_function_call; bool retpoline_safe; + bool retpoline_ret; u8 visited; struct symbol *call_dest; struct instruction *jump_dest; -- 2.18.2