From patchwork Thu Jun 11 10:03:03 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Torsten Duwe X-Patchwork-Id: 483035 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [103.22.144.68]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id A4AA81402AD for ; Thu, 11 Jun 2015 20:05:12 +1000 (AEST) Received: from ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 8ABDD1A1ADD for ; Thu, 11 Jun 2015 20:05:12 +1000 (AEST) X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Received: from newverein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id BA14B1A0FF6 for ; Thu, 11 Jun 2015 20:03:06 +1000 (AEST) Received: by newverein.lst.de (Postfix, from userid 2005) id 60F39691CA; Thu, 11 Jun 2015 12:03:03 +0200 (CEST) Date: Thu, 11 Jun 2015 12:03:03 +0200 From: Torsten Duwe To: Steven Rostedt , Michael Ellerman Subject: [PATCH 4/4] ppc64 ftrace_with_regs recursion protection Message-ID: <20150611100303.GE4492@lst.de> References: <20150611095338.GA4492@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20150611095338.GA4492@lst.de> User-Agent: Mutt/1.5.17 (2007-11-01) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jiri Kosina , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" This is an *emergency* parachute to avoid an endless recursion and consecutively a kernel stack overflow, should any function within some ftrace framework cause an access fault, which calls _mcount / ftrace_caller in return and so on. It might also call an ftrace'd function directly. As Michael Ellerman pointed out, it is a tedious and error-prone task to maintain a complete list of those functions that _might_ get called from *_access_fault or any dynamic tracer function. So we'll concentrate on the most frequent cases to enhance performance later, while for now sticking with this fill-in. It will later serve as a backup protection. * arch/powerpc/kernel/entry_64.S: - test-and-set TRACE_FTRACE_BIT in task_struct's trace_recursion, do not call the actual tracer function if set, clear flag on return. Signed-off-by: Torsten Duwe --- arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/entry_64.S | 15 +++++++++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) -- diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 4717859..ae10752 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -72,6 +72,7 @@ int main(void) DEFINE(THREAD, offsetof(struct task_struct, thread)); DEFINE(MM, offsetof(struct task_struct, mm)); DEFINE(MMCONTEXTID, offsetof(struct mm_struct, context.id)); + DEFINE(TASK_TRACEREC, offsetof(struct task_struct, trace_recursion)); #ifdef CONFIG_PPC64 DEFINE(AUDITCONTEXT, offsetof(struct task_struct, audit_context)); DEFINE(SIGSEGV, SIGSEGV); diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index a4132ef..4768104 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -1202,7 +1202,13 @@ _GLOBAL(ftrace_caller) SAVE_8GPRS(16,r1) SAVE_8GPRS(24,r1) - + ld r3, PACACURRENT(r13) + ld r4, TASK_TRACEREC(r3) + andi. r5, r4, 0x0010 // ( 1 << TRACE_FTRACE_BIT ) + ori r4, r4, 0x0010 + std r4, TASK_TRACEREC(r3) + bne- 3f // ftrace in progress - avoid recursion! + LOAD_REG_IMMEDIATE(r3,function_trace_op) ld r5,0(r3) @@ -1224,9 +1230,14 @@ ftrace_call: bl ftrace_stub nop + ld r3, PACACURRENT(r13) + ld r4, TASK_TRACEREC(r3) + andi. r4, r4, 0xffef // ~( 1 << TRACE_FTRACE_BIT ) + std r4, TASK_TRACEREC(r3) + ld r3, _NIP(r1) mtlr r3 - +3: REST_8GPRS(0,r1) REST_8GPRS(8,r1) REST_8GPRS(16,r1)