From patchwork Tue Nov 25 10:37:21 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 414410 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 34ACA1401B5; Tue, 25 Nov 2014 21:42:53 +1100 (AEDT) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1XtDa5-0003QB-FX; Tue, 25 Nov 2014 10:42:49 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1XtDYo-0002bV-JP for kernel-team@lists.ubuntu.com; Tue, 25 Nov 2014 10:41:30 +0000 Received: from bl15-150-46.dsl.telepac.pt ([188.80.150.46] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1XtDYo-0001sY-Cm; Tue, 25 Nov 2014 10:41:30 +0000 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 3.16.y-ckt 091/254] x86, fpu: shift drop_init_fpu() from save_xstate_sig() to handle_signal() Date: Tue, 25 Nov 2014 10:37:21 +0000 Message-Id: <1416912004-5928-92-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1416912004-5928-1-git-send-email-luis.henriques@canonical.com> References: <1416912004-5928-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Cc: "H. Peter Anvin" , Oleg Nesterov X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com 3.16.7-ckt2 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 66463db4fc5605d51c7bb81d009d5bf30a783a2c upstream. save_xstate_sig()->drop_init_fpu() doesn't look right. setup_rt_frame() can fail after that, in this case the next setup_rt_frame() triggered by SIGSEGV won't save fpu simply because the old state was lost. This obviously mean that fpu won't be restored after sys_rt_sigreturn() from SIGSEGV handler. Shift drop_init_fpu() into !failed branch in handle_signal(). Test-case (needs -O2): #include #include #include #include #include #include #include volatile double D; void test(double d) { int pid = getpid(); for (D = d; D == d; ) { /* sys_tkill(pid, SIGHUP); asm to avoid save/reload * fp regs around "C" call */ asm ("" : : "a"(200), "D"(pid), "S"(1)); asm ("syscall" : : : "ax"); } printf("ERR!!\n"); } void sigh(int sig) { } char altstack[4096 * 10] __attribute__((aligned(4096))); void *tfunc(void *arg) { for (;;) { mprotect(altstack, sizeof(altstack), PROT_READ); mprotect(altstack, sizeof(altstack), PROT_READ|PROT_WRITE); } } int main(void) { stack_t st = { .ss_sp = altstack, .ss_size = sizeof(altstack), .ss_flags = SS_ONSTACK, }; struct sigaction sa = { .sa_handler = sigh, }; pthread_t pt; sigaction(SIGSEGV, &sa, NULL); sigaltstack(&st, NULL); sa.sa_flags = SA_ONSTACK; sigaction(SIGHUP, &sa, NULL); pthread_create(&pt, NULL, tfunc, NULL); test(123.456); return 0; } Reported-by: Bean Anderson Signed-off-by: Oleg Nesterov Link: http://lkml.kernel.org/r/20140902175713.GA21646@redhat.com Signed-off-by: H. Peter Anvin Signed-off-by: Luis Henriques --- arch/x86/kernel/signal.c | 5 +++++ arch/x86/kernel/xsave.c | 2 -- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 2851d63c1202..ed37a768d0fc 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -675,6 +675,11 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs) * handler too. */ regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF); + /* + * Ensure the signal handler starts with the new fpu state. + */ + if (used_math()) + drop_init_fpu(current); } signal_setup_done(failed, ksig, test_thread_flag(TIF_SINGLESTEP)); } diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c index 4679ef4005da..dd50e26c58f6 100644 --- a/arch/x86/kernel/xsave.c +++ b/arch/x86/kernel/xsave.c @@ -268,8 +268,6 @@ int save_xstate_sig(void __user *buf, void __user *buf_fx, int size) if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate)) return -1; - drop_init_fpu(tsk); /* trigger finit */ - return 0; }