Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752540AbaGVByA (ORCPT ); Mon, 21 Jul 2014 21:54:00 -0400 Received: from mail-pa0-f53.google.com ([209.85.220.53]:54701 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751317AbaGVBx6 (ORCPT ); Mon, 21 Jul 2014 21:53:58 -0400 From: Andy Lutomirski To: linux-kernel@vger.kernel.org, Kees Cook , Will Drewry Cc: Oleg Nesterov , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux-arch@vger.kernel.org, linux-security-module@vger.kernel.org, Alexei Starovoitov , hpa@zytor.com, Andy Lutomirski Subject: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases Date: Mon, 21 Jul 2014 18:53:41 -0700 Message-Id: <3f649f5658a163645e3ce15156176c325283762e.1405992946.git.luto@amacapital.net> X-Mailer: git-send-email 1.9.3 In-Reply-To: <2baeb5fad958c292705885941d61ab31771a75bb.1405992946.git.luto@amacapital.net> References: <2baeb5fad958c292705885941d61ab31771a75bb.1405992946.git.luto@amacapital.net> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This splits syscall_trace_enter into syscall_trace_enter_phase1 and syscall_trace_enter_phase2. Only phase 2 has full pt_regs, and only phase 2 is permitted to modify any of pt_regs except for orig_ax. The intent is that phase 1 can be called from the syscall fast path. Signed-off-by: Andy Lutomirski --- arch/x86/include/asm/ptrace.h | 5 ++ arch/x86/kernel/ptrace.c | 145 ++++++++++++++++++++++++++++++++++++------ 2 files changed, 131 insertions(+), 19 deletions(-) diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 6205f0c..86fc2bb 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -75,6 +75,11 @@ convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs); extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code, int si_code); + +extern unsigned long syscall_trace_enter_phase1(struct pt_regs *, u32 arch); +extern long syscall_trace_enter_phase2(struct pt_regs *, u32 arch, + unsigned long phase1_result); + extern long syscall_trace_enter(struct pt_regs *); extern void syscall_trace_leave(struct pt_regs *); diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 39296d2..9ec6972 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -1441,13 +1441,117 @@ void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, force_sig_info(SIGTRAP, &info, tsk); } +static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) +{ +#ifdef CONFIG_X86_64 + if (arch == AUDIT_ARCH_X86_64) { + audit_syscall_entry(arch, regs->orig_ax, regs->di, + regs->si, regs->dx, regs->r10); + } else +#endif + { + audit_syscall_entry(arch, regs->orig_ax, regs->bx, + regs->cx, regs->dx, regs->si); + } +} + /* - * We must return the syscall number to actually look up in the table. - * This can be -1L to skip running any syscall at all. + * We can return 0 to resume the syscall or anything else to go to phase + * 2. If we resume the syscall, we need to put something appropriate in + * regs->orig_ax. + * + * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax + * are fully functional. + * + * For phase 2's benefit, our return value is: + * 0: resume the syscall + * 1: go to phase 2; no seccomp phase 2 needed + * 2: go to phase 2; pass return value to seccomp */ -long syscall_trace_enter(struct pt_regs *regs) +unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) +{ + unsigned long ret = 0; + u32 work; + + BUG_ON(regs != task_pt_regs(current)); + + work = ACCESS_ONCE(current_thread_info()->flags) & + _TIF_WORK_SYSCALL_ENTRY; + +#ifdef CONFIG_SECCOMP + /* + * Do seccomp first -- it should minimize exposure of other + * code, and keeping seccomp fast is probably more valuable + * than the rest of this. + */ + if (work & _TIF_SECCOMP) { + struct seccomp_data sd; + + sd.arch = arch; + sd.nr = regs->orig_ax; + sd.instruction_pointer = regs->ip; +#ifdef CONFIG_X86_64 + if (arch == AUDIT_ARCH_X86_64) { + sd.args[0] = regs->di; + sd.args[1] = regs->si; + sd.args[2] = regs->dx; + sd.args[3] = regs->r10; + sd.args[4] = regs->r8; + sd.args[5] = regs->r9; + } else +#endif + { + sd.args[0] = regs->bx; + sd.args[1] = regs->cx; + sd.args[2] = regs->dx; + sd.args[3] = regs->si; + sd.args[4] = regs->di; + sd.args[5] = regs->bp; + } + + BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0); + BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1); + + ret = seccomp_phase1(&sd); + if (ret == SECCOMP_PHASE1_SKIP) { + regs->orig_ax = -1; + ret = 0; + } else if (ret != SECCOMP_PHASE1_OK) { + return ret; /* Go directly to phase 2 */ + } + + work &= ~_TIF_SECCOMP; + } +#endif + + /* Do our best to finish without phase 2. */ + if (work == 0) + return ret; /* seccomp only (ret == 0 here) */ + +#ifdef CONFIG_AUDITSYSCALL + if (work == _TIF_SYSCALL_AUDIT) { + /* + * If there is no more work to be done except auditing, + * then audit in phase 1. Phase 2 always audits, so, if + * we audit here, then we can't go on to phase 2. + */ + do_audit_syscall_entry(regs, arch); + return 0; + } +#endif + + return 1; /* Something is enabled that we can't handle in phase 1 */ +} + +/* Returns the syscall nr to run (which should match regs->orig_ax). */ +long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch, + unsigned long phase1_result) { long ret = 0; + u32 work = ACCESS_ONCE(current_thread_info()->flags) & + _TIF_WORK_SYSCALL_ENTRY; + + BUG_ON(regs != task_pt_regs(current)); user_exit(); @@ -1458,17 +1562,20 @@ long syscall_trace_enter(struct pt_regs *regs) * do_debug() and we need to set it again to restore the user * state. If we entered on the slow path, TF was already set. */ - if (test_thread_flag(TIF_SINGLESTEP)) + if (work & _TIF_SINGLESTEP) regs->flags |= X86_EFLAGS_TF; - /* do the secure computing check first */ - if (secure_computing()) { + /* + * Call seccomp_phase2 before running the other hooks so that + * they can see any changes made by a seccomp tracer. + */ + if (phase1_result > 1 && seccomp_phase2(phase1_result)) { /* seccomp failures shouldn't expose any additional code. */ ret = -1L; goto out; } - if (unlikely(test_thread_flag(TIF_SYSCALL_EMU))) + if (unlikely(work & _TIF_SYSCALL_EMU)) ret = -1L; if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) && @@ -1478,23 +1585,23 @@ long syscall_trace_enter(struct pt_regs *regs) if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) trace_sys_enter(regs, regs->orig_ax); - if (is_ia32_task()) - audit_syscall_entry(AUDIT_ARCH_I386, - regs->orig_ax, - regs->bx, regs->cx, - regs->dx, regs->si); -#ifdef CONFIG_X86_64 - else - audit_syscall_entry(AUDIT_ARCH_X86_64, - regs->orig_ax, - regs->di, regs->si, - regs->dx, regs->r10); -#endif + do_audit_syscall_entry(regs, arch); out: return ret ?: regs->orig_ax; } +long syscall_trace_enter(struct pt_regs *regs) +{ + u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; + unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch); + + if (phase1_result == 0) + return regs->orig_ax; + else + return syscall_trace_enter_phase2(regs, arch, phase1_result); +} + void syscall_trace_leave(struct pt_regs *regs) { bool step; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/