From patchwork Tue Nov 20 20:35:36 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nadav Amit X-Patchwork-Id: 10691863 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2B34E14DE for ; Wed, 21 Nov 2018 03:53:33 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1538A28066 for ; Wed, 21 Nov 2018 03:53:33 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id EE7B32852B; Wed, 21 Nov 2018 03:53:32 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.4 required=2.0 tests=BAYES_00,DATE_IN_PAST_06_12, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6CD4C2849D for ; Wed, 21 Nov 2018 03:53:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726877AbeKUO0I (ORCPT ); Wed, 21 Nov 2018 09:26:08 -0500 Received: from ex13-edg-ou-001.vmware.com ([208.91.0.189]:13925 "EHLO EX13-EDG-OU-001.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726406AbeKUO0I (ORCPT ); Wed, 21 Nov 2018 09:26:08 -0500 Received: from sc9-mailhost2.vmware.com (10.113.161.72) by EX13-EDG-OU-001.vmware.com (10.113.208.155) with Microsoft SMTP Server id 15.0.1156.6; Tue, 20 Nov 2018 19:52:52 -0800 Received: from sc2-haas01-esx0118.eng.vmware.com (sc2-haas01-esx0118.eng.vmware.com [10.172.44.118]) by sc9-mailhost2.vmware.com (Postfix) with ESMTP id 390D3B1872; Tue, 20 Nov 2018 22:53:30 -0500 (EST) From: Nadav Amit To: Ingo Molnar CC: , , "H. Peter Anvin" , Thomas Gleixner , Borislav Petkov , Dave Hansen , Peter Zijlstra , , , , Nadav Amit , Andy Lutomirski , Kees Cook , Dave Hansen , Masami Hiramatsu Subject: [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Date: Tue, 20 Nov 2018 12:35:36 -0800 Message-ID: <20181120203545.34928-2-namit@vmware.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181120203545.34928-1-namit@vmware.com> References: <20181120203545.34928-1-namit@vmware.com> MIME-Version: 1.0 Received-SPF: None (EX13-EDG-OU-001.vmware.com: namit@vmware.com does not designate permitted sender hosts) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP text_mutex is currently expected to be held before text_poke() is called, but we kgdb does not take the mutex, and instead *supposedly* ensures the lock is not taken and will not be acquired by any other core while text_poke() is running. The reason for the "supposedly" comment is that it is not entirely clear that this would be the case if gdb_do_roundup is zero. This patch creates two wrapper functions, text_poke() and text_poke_kgdb() which do or do not run the lockdep assertion respectively. While we are at it, change the return code of text_poke() to something meaningful. One day, callers might actually respect it and the existing BUG_ON() when patching fails could be removed. For kgdb, the return value can actually be used. Cc: Andy Lutomirski Cc: Kees Cook Cc: Dave Hansen Cc: Masami Hiramatsu Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()") Suggested-by: Peter Zijlstra Acked-by: Jiri Kosina Signed-off-by: Nadav Amit --- arch/x86/include/asm/text-patching.h | 1 + arch/x86/kernel/alternative.c | 52 ++++++++++++++++++++-------- arch/x86/kernel/kgdb.c | 11 +++--- 3 files changed, 45 insertions(+), 19 deletions(-) diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index e85ff65c43c3..f8fc8e86cf01 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -35,6 +35,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len); * inconsistent instruction while you patch. */ extern void *text_poke(void *addr, const void *opcode, size_t len); +extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len); extern int poke_int3_handler(struct pt_regs *regs); extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler); extern int after_bootmem; diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index ebeac487a20c..c6a3a10a2fd5 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -678,18 +678,7 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode, return addr; } -/** - * text_poke - Update instructions on a live kernel - * @addr: address to modify - * @opcode: source of the copy - * @len: length to copy - * - * Only atomic text poke/set should be allowed when not doing early patching. - * It means the size must be writable atomically and the address must be aligned - * in a way that permits an atomic write. It also makes sure we fit on a single - * page. - */ -void *text_poke(void *addr, const void *opcode, size_t len) +static void *__text_poke(void *addr, const void *opcode, size_t len) { unsigned long flags; char *vaddr; @@ -702,8 +691,6 @@ void *text_poke(void *addr, const void *opcode, size_t len) */ BUG_ON(!after_bootmem); - lockdep_assert_held(&text_mutex); - if (!core_kernel_text((unsigned long)addr)) { pages[0] = vmalloc_to_page(addr); pages[1] = vmalloc_to_page(addr + PAGE_SIZE); @@ -732,6 +719,43 @@ void *text_poke(void *addr, const void *opcode, size_t len) return addr; } +/** + * text_poke - Update instructions on a live kernel + * @addr: address to modify + * @opcode: source of the copy + * @len: length to copy + * + * Only atomic text poke/set should be allowed when not doing early patching. + * It means the size must be writable atomically and the address must be aligned + * in a way that permits an atomic write. It also makes sure we fit on a single + * page. + */ +void *text_poke(void *addr, const void *opcode, size_t len) +{ + lockdep_assert_held(&text_mutex); + + return __text_poke(addr, opcode, len); +} + +/** + * text_poke_kgdb - Update instructions on a live kernel by kgdb + * @addr: address to modify + * @opcode: source of the copy + * @len: length to copy + * + * Only atomic text poke/set should be allowed when not doing early patching. + * It means the size must be writable atomically and the address must be aligned + * in a way that permits an atomic write. It also makes sure we fit on a single + * page. + * + * Context: should only be used by kgdb, which ensures no other core is running, + * despite the fact it does not hold the text_mutex. + */ +void *text_poke_kgdb(void *addr, const void *opcode, size_t len) +{ + return __text_poke(addr, opcode, len); +} + static void do_sync_core(void *info) { sync_core(); diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index 8e36f249646e..2636ca8394bd 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -763,13 +763,13 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt) if (!err) return err; /* - * It is safe to call text_poke() because normal kernel execution + * It is safe to call text_poke_kgdb() because normal kernel execution * is stopped on all cores, so long as the text_mutex is not locked. */ if (mutex_is_locked(&text_mutex)) return -EBUSY; - text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, - BREAK_INSTR_SIZE); + text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, + BREAK_INSTR_SIZE); err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); if (err) return err; @@ -788,12 +788,13 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt) if (bpt->type != BP_POKE_BREAKPOINT) goto knl_write; /* - * It is safe to call text_poke() because normal kernel execution + * It is safe to call text_poke_kgdb() because normal kernel execution * is stopped on all cores, so long as the text_mutex is not locked. */ if (mutex_is_locked(&text_mutex)) goto knl_write; - text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE); + text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr, + BREAK_INSTR_SIZE); err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE)) goto knl_write;