From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754815AbcFUAGG (ORCPT ); Mon, 20 Jun 2016 20:06:06 -0400 Received: from mail.kernel.org ([198.145.29.136]:60634 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752159AbcFUAFa (ORCPT ); Mon, 20 Jun 2016 20:05:30 -0400 From: Andy Lutomirski To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: Borislav Petkov , Andy Lutomirski , Pedro Alves , Oleg Nesterov , Kees Cook Subject: [PATCH v3 1/3] x86/ptrace: Stop setting TS_COMPAT in ptrace code Date: Mon, 20 Jun 2016 16:39:52 -0700 Message-Id: <8bacd629dcdbb97ee0626912c27a4a09f991b5dd.1466464928.git.luto@kernel.org> X-Mailer: git-send-email 2.5.5 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Setting TS_COMPAT in ptrace is wrong: if we happen to do it during syscall entry, then we'll confuse seccomp and audit. (The former isn't a security problem: seccomp is currently entirely insecure if a malicious ptracer is attached.) As a minimal fix, this patch adds a new flag TS_I386_REGS_POKED that handles the ptrace special case. Cc: Pedro Alves Cc: Oleg Nesterov Cc: Kees Cook Signed-off-by: Andy Lutomirski --- arch/x86/entry/common.c | 6 +++++- arch/x86/include/asm/syscall.h | 5 +---- arch/x86/include/asm/thread_info.h | 3 +++ arch/x86/kernel/ptrace.c | 15 +++++++++------ arch/x86/kernel/signal.c | 26 ++++++++++++++++++++++++-- 5 files changed, 42 insertions(+), 13 deletions(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index ec138e538c44..0db497a8ff19 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -270,8 +270,12 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) * handling, because syscall restart has a fixup for compat * syscalls. The fixup is exercised by the ptrace_syscall_32 * selftest. + * + * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer + * special case only applies after poking regs and before the + * very next return to user mode. */ - ti->status &= ~TS_COMPAT; + ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); #endif user_enter(); diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h index 999b7cd2e78c..4e23dd15c661 100644 --- a/arch/x86/include/asm/syscall.h +++ b/arch/x86/include/asm/syscall.h @@ -60,7 +60,7 @@ static inline long syscall_get_error(struct task_struct *task, * TS_COMPAT is set for 32-bit syscall entries and then * remains set until we return to user mode. */ - if (task_thread_info(task)->status & TS_COMPAT) + if (task_thread_info(task)->status & (TS_COMPAT|TS_I386_REGS_POKED)) /* * Sign-extend the value so (int)-EFOO becomes (long)-EFOO * and will match correctly in comparisons. @@ -239,9 +239,6 @@ static inline int syscall_get_arch(void) * TS_COMPAT is set for 32-bit syscall entry and then * remains set until we return to user mode. * - * TIF_IA32 tasks should always have TS_COMPAT set at - * system call time. - * * x32 tasks should be considered AUDIT_ARCH_X86_64. */ if (task_thread_info(current)->status & TS_COMPAT) diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 30c133ac05cd..4bca518d11f4 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -228,6 +228,9 @@ static inline unsigned long current_stack_pointer(void) * have to worry about atomic accesses. */ #define TS_COMPAT 0x0002 /* 32bit syscall active (64BIT)*/ +#ifdef CONFIG_COMPAT +#define TS_I386_REGS_POKED 0x0004 /* regs poked by 32-bit ptracer */ +#endif #define TS_RESTORE_SIGMASK 0x0008 /* restore signal mask in do_signal() */ #ifndef __ASSEMBLY__ diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 600edd225e81..f79576a541ff 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -923,15 +923,18 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 value) case offsetof(struct user32, regs.orig_eax): /* - * A 32-bit debugger setting orig_eax means to restore - * the state of the task restarting a 32-bit syscall. - * Make sure we interpret the -ERESTART* codes correctly - * in case the task is not actually still sitting at the - * exit from a 32-bit syscall with TS_COMPAT still set. + * Warning: bizarre corner case fixup here. A 32-bit + * debugger setting orig_eax to -1 wants to disable + * syscall restart. Make sure that the syscall + * restart code sign-extends orig_ax. Also make sure + * we interpret the -ERESTART* codes correctly if + * loaded into regs->ax in case the task is not + * actually still sitting at the exit from a 32-bit + * syscall with TS_COMPAT still set. */ regs->orig_ax = value; if (syscall_get_nr(child, regs) >= 0) - task_thread_info(child)->status |= TS_COMPAT; + task_thread_info(child)->status |= TS_I386_REGS_POKED; break; case offsetof(struct user32, regs.eflags): diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 22cc2f9f8aec..6b952e1d8db8 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -760,8 +760,30 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs) static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs) { -#ifdef CONFIG_X86_64 - if (in_ia32_syscall()) + /* + * This function is fundamentally broken as currently + * implemented. + * + * The idea is that we want to trigger a call to the + * restart_block() syscall and that we want in_ia32_syscall(), + * in_x32_syscall(), etc. to match whatever they were in the + * syscall being restarted. We assume that the syscall + * instruction at (regs->ip - 2) matches whatever syscall + * instruction we used to enter in the first place. + * + * The problem is that we can get here when ptrace pokes + * syscall-like values into regs even if we're not in a syscall + * at all. + * + * For now, we maintain historical behavior and guess based on + * stored state. We could do better by saving the actual + * syscall arch in restart_block or (with caveats on x32) by + * checking if regs->ip points to 'int $0x80'. The current + * behavior is incorrect if a tracer has a different bitness + * than the tracee. + */ +#ifdef CONFIG_IA32_EMULATION + if (current_thread_info()->status & (TS_COMPAT|TS_I386_REGS_POKED)) return __NR_ia32_restart_syscall; #endif #ifdef CONFIG_X86_X32_ABI -- 2.5.5