From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760247Ab2C2Wtj (ORCPT ); Thu, 29 Mar 2012 18:49:39 -0400 Received: from mail1.windriver.com ([147.11.146.13]:56166 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760257Ab2C2WtU (ORCPT ); Thu, 29 Mar 2012 18:49:20 -0400 From: Jason Wessel To: CC: Subject: [PATCH 6/6] x86,kgdb: Fix DEBUG_RODATA limitation using text_poke() Date: Thu, 29 Mar 2012 17:49:02 -0500 Message-ID: <1333061342-10132-7-git-send-email-jason.wessel@windriver.com> X-Mailer: git-send-email 1.7.9.4 In-Reply-To: <1333061342-10132-1-git-send-email-jason.wessel@windriver.com> References: <1333061342-10132-1-git-send-email-jason.wessel@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There has long been a limitation using software breakpoints with a kernel compiled with CONFIG_DEBUG_RODATA going back to 2.6.26. For this particular patch, it will apply cleanly and has been tested all the way back to 2.6.36. The kprobes code uses the text_poke() function which accommodates writing a breakpoint into a read-only page. The x86 kgdb code can solve the problem similarly by overriding the default breakpoint set/remove routines and using text_poke() directly. The x86 kgdb code will first attempt to use the traditional probe_kernel_write(), and next try using a the text_poke() function. The break point install method is tracked such that the correct break point removal routine will get called later on. Cc: x86@kernel.org Cc: Thomas Gleixner Cc: Ingo Molnar Cc: H. Peter Anvin Cc: stable@vger.kernel.org # >= 2.6.36 Inspried-by: Masami Hiramatsu Signed-off-by: Jason Wessel --- arch/x86/kernel/kgdb.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/kgdb.h | 3 ++- 2 files changed, 62 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index fdc37b3..b9bd9d8 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -43,6 +43,8 @@ #include #include #include +#include +#include #include #include @@ -742,6 +744,64 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip) regs->ip = ip; } +int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt) +{ + int err; + char opc[BREAK_INSTR_SIZE]; + + bpt->type = BP_BREAKPOINT; + err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr, + BREAK_INSTR_SIZE); + if (err) + return err; + err = probe_kernel_write((char *)bpt->bpt_addr, + arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE); +#ifdef CONFIG_DEBUG_RODATA + if (!err) + return err; + /* + * It is safe to call text_poke() 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); + err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); + if (err) + return err; + if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE)) + return -EINVAL; + bpt->type = BP_POKE_BREAKPOINT; +#endif /* CONFIG_DEBUG_RODATA */ + return err; +} + +int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt) +{ +#ifdef CONFIG_DEBUG_RODATA + int err; + char opc[BREAK_INSTR_SIZE]; + + if (bpt->type != BP_POKE_BREAKPOINT) + goto knl_write; + /* + * It is safe to call text_poke() 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); + 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; + return err; +knl_write: +#endif /* CONFIG_DEBUG_RODATA */ + return probe_kernel_write((char *)bpt->bpt_addr, + (char *)bpt->saved_instr, BREAK_INSTR_SIZE); +} + struct kgdb_arch arch_kgdb_ops = { /* Breakpoint instruction: */ .gdb_bpt_instr = { 0xcc }, diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index e5d689c..c4d2fc1 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -63,7 +63,8 @@ enum kgdb_bptype { BP_HARDWARE_BREAKPOINT, BP_WRITE_WATCHPOINT, BP_READ_WATCHPOINT, - BP_ACCESS_WATCHPOINT + BP_ACCESS_WATCHPOINT, + BP_POKE_BREAKPOINT, }; enum kgdb_bpstate { -- 1.7.9.4