From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Subject: Re: [RFC PATCH 1/6] x86/alternative: assert text_mutex is taken Date: Wed, 29 Aug 2018 17:59:36 +0900 Message-ID: <20180829175936.fb27b3bf13da819a9a971f07@kernel.org> References: <20180829081147.184610-1-namit@vmware.com> <20180829081147.184610-2-namit@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180829081147.184610-2-namit@vmware.com> Sender: linux-kernel-owner@vger.kernel.org To: Nadav Amit Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Ingo Molnar , x86@kernel.org, Arnd Bergmann , linux-arch@vger.kernel.org, Andy Lutomirski , Masami Hiramatsu , Kees Cook List-Id: linux-arch.vger.kernel.org On Wed, 29 Aug 2018 01:11:42 -0700 Nadav Amit wrote: > Use lockdep to ensure that text_mutex is taken when text_poke() is > called. > > Actually it is not always taken, specifically when it is called by kgdb, > so take the lock in these cases. Can we really take a mutex in kgdb context? kgdb_arch_remove_breakpoint <- dbg_deactivate_sw_breakpoints <- kgdb_reenter_check <- kgdb_handle_exception <- __kgdb_notify <- kgdb_ll_trap <- do_int3 <- kgdb_notify <- die notifier kgdb_arch_set_breakpoint <- dbg_activate_sw_breakpoints <- kgdb_reenter_check <- kgdb_handle_exception ... Both seems called in exception context, so we can not take a mutex lock. I think kgdb needs a special path. Thanks, > > Cc: Andy Lutomirski > Cc: Masami Hiramatsu > Cc: Kees Cook > Suggested-by: Peter Zijlstra > Signed-off-by: Nadav Amit > --- > arch/x86/kernel/alternative.c | 1 + > arch/x86/kernel/kgdb.c | 9 +++++++++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 014f214da581..916c11b410c4 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -699,6 +699,7 @@ void *text_poke(void *addr, const void *opcode, size_t len) > * pages as they are not yet initialized. > */ > BUG_ON(!after_bootmem); > + lockdep_assert_held(&text_mutex); > > if (!core_kernel_text((unsigned long)addr)) { > pages[0] = vmalloc_to_page(addr); > diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c > index 8e36f249646e..60b99c76086c 100644 > --- a/arch/x86/kernel/kgdb.c > +++ b/arch/x86/kernel/kgdb.c > @@ -768,8 +768,12 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt) > */ > if (mutex_is_locked(&text_mutex)) > return -EBUSY; > + > + /* Take the mutex to avoid lockdep assertion failures. */ > + mutex_lock(&text_mutex); > text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, > BREAK_INSTR_SIZE); > + mutex_unlock(&text_mutex); > err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); > if (err) > return err; > @@ -793,7 +797,12 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt) > */ > if (mutex_is_locked(&text_mutex)) > goto knl_write; > + > + /* Take the mutex to avoid lockdep assertion failures. */ > + mutex_lock(&text_mutex); > text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE); > + mutex_unlock(&text_mutex); > + > 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; > -- > 2.17.1 > -- Masami Hiramatsu From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:33474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727133AbeH2Mze (ORCPT ); Wed, 29 Aug 2018 08:55:34 -0400 Date: Wed, 29 Aug 2018 17:59:36 +0900 From: Masami Hiramatsu Subject: Re: [RFC PATCH 1/6] x86/alternative: assert text_mutex is taken Message-ID: <20180829175936.fb27b3bf13da819a9a971f07@kernel.org> In-Reply-To: <20180829081147.184610-2-namit@vmware.com> References: <20180829081147.184610-1-namit@vmware.com> <20180829081147.184610-2-namit@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Nadav Amit Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Ingo Molnar , x86@kernel.org, Arnd Bergmann , linux-arch@vger.kernel.org, Andy Lutomirski , Masami Hiramatsu , Kees Cook Message-ID: <20180829085936.ySVcL3TTWrBetIJgRcPjIpLZJ03cFBggx48uo4H-BpU@z> On Wed, 29 Aug 2018 01:11:42 -0700 Nadav Amit wrote: > Use lockdep to ensure that text_mutex is taken when text_poke() is > called. > > Actually it is not always taken, specifically when it is called by kgdb, > so take the lock in these cases. Can we really take a mutex in kgdb context? kgdb_arch_remove_breakpoint <- dbg_deactivate_sw_breakpoints <- kgdb_reenter_check <- kgdb_handle_exception <- __kgdb_notify <- kgdb_ll_trap <- do_int3 <- kgdb_notify <- die notifier kgdb_arch_set_breakpoint <- dbg_activate_sw_breakpoints <- kgdb_reenter_check <- kgdb_handle_exception ... Both seems called in exception context, so we can not take a mutex lock. I think kgdb needs a special path. Thanks, > > Cc: Andy Lutomirski > Cc: Masami Hiramatsu > Cc: Kees Cook > Suggested-by: Peter Zijlstra > Signed-off-by: Nadav Amit > --- > arch/x86/kernel/alternative.c | 1 + > arch/x86/kernel/kgdb.c | 9 +++++++++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 014f214da581..916c11b410c4 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -699,6 +699,7 @@ void *text_poke(void *addr, const void *opcode, size_t len) > * pages as they are not yet initialized. > */ > BUG_ON(!after_bootmem); > + lockdep_assert_held(&text_mutex); > > if (!core_kernel_text((unsigned long)addr)) { > pages[0] = vmalloc_to_page(addr); > diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c > index 8e36f249646e..60b99c76086c 100644 > --- a/arch/x86/kernel/kgdb.c > +++ b/arch/x86/kernel/kgdb.c > @@ -768,8 +768,12 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt) > */ > if (mutex_is_locked(&text_mutex)) > return -EBUSY; > + > + /* Take the mutex to avoid lockdep assertion failures. */ > + mutex_lock(&text_mutex); > text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, > BREAK_INSTR_SIZE); > + mutex_unlock(&text_mutex); > err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); > if (err) > return err; > @@ -793,7 +797,12 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt) > */ > if (mutex_is_locked(&text_mutex)) > goto knl_write; > + > + /* Take the mutex to avoid lockdep assertion failures. */ > + mutex_lock(&text_mutex); > text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE); > + mutex_unlock(&text_mutex); > + > 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; > -- > 2.17.1 > -- Masami Hiramatsu