From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 19 Apr 2002 20:10:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 19 Apr 2002 20:10:48 -0400 Received: from rwcrmhc51.attbi.com ([204.127.198.38]:25501 "EHLO rwcrmhc51.attbi.com") by vger.kernel.org with ESMTP id ; Fri, 19 Apr 2002 20:10:41 -0400 Message-ID: <3CC0B16F.1050501@didntduck.org> Date: Fri, 19 Apr 2002 20:08:15 -0400 From: Brian Gerst User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9) Gecko/20020311 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Linus Torvalds CC: "H. Peter Anvin" , andrea@suse.de, ak@suse.de, linux-kernel@vger.kernel.org, jh@suse.cz Subject: Re: [PATCH] Re: SSE related security hole In-Reply-To: Content-Type: multipart/mixed; boundary="------------090405060502080603080707" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------090405060502080603080707 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Linus Torvalds wrote: > > On Fri, 19 Apr 2002, Brian Gerst wrote: > >>Here's a patch to do just that. It initializes the saved state in the >>task struct and falls through to restore_fpu(). > > > One issue is whether we _can_ restore a "generated" image like this: it's > entirely possible that Intel might save away internal CPU shadow data in > the save-state structure, and future CPU's might be unhappy about loading > data that doesn't conform to what the CPU would save. > > That said, the same issue is certainly true for just doing "xorps", since > that will not clear any potential future CPU state. > > I get this feeling that Intel screwed up on specifying how to initialize > this whole state. > > Linus > I don't know about Intel, but the Athlon doesn't appear to save anything in the "reserved" areas. The values that I use to initialize the state are from what is saved after loading the stack with zeroes (fldz) and then doing finit. I have samples of the saved state from a P2, a K6-2, and an Athlon XP. Attached is a revised patch. I had the cpu_has_xmm test wrong. -- Brian Gerst --------------090405060502080603080707 Content-Type: text/plain; name="fpuclear-2" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="fpuclear-2" diff -urN linux-2.5.8/arch/i386/kernel/i387.c linux/arch/i386/kernel/i387.c --- linux-2.5.8/arch/i386/kernel/i387.c Thu Mar 7 21:18:32 2002 +++ linux/arch/i386/kernel/i387.c Fri Apr 19 19:35:14 2002 @@ -31,13 +31,21 @@ * value at reset if we support XMM instructions and then * remeber the current task has used the FPU. */ -void init_fpu(void) +void init_fpu(struct task_struct *tsk) { - __asm__("fninit"); - if ( cpu_has_xmm ) - load_mxcsr(0x1f80); - - current->used_math = 1; + if (cpu_has_fxsr) { + memset(&tsk->thread.i387.fxsave, 0, sizeof(struct i387_fxsave_struct)); + tsk->thread.i387.fxsave.cwd = 0x37f; + if (cpu_has_xmm) + tsk->thread.i387.fxsave.mxcsr = 0x1f80; + } else { + memset(&tsk->thread.i387.fsave, 0, sizeof(struct i387_fsave_struct)); + tsk->thread.i387.fsave.cwd = 0xffff037f; + tsk->thread.i387.fsave.swd = 0xffff0000; + tsk->thread.i387.fsave.twd = 0xffffffff; + tsk->thread.i387.fsave.fos = 0xffff0000; + } + tsk->used_math = 1; } /* diff -urN linux-2.5.8/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c --- linux-2.5.8/arch/i386/kernel/traps.c Sun Apr 14 23:48:18 2002 +++ linux/arch/i386/kernel/traps.c Fri Apr 19 18:22:12 2002 @@ -757,13 +757,12 @@ */ asmlinkage void math_state_restore(struct pt_regs regs) { + struct task_struct *tsk = current; clts(); /* Allow maths ops (or we recurse) */ - if (current->used_math) { - restore_fpu(current); - } else { - init_fpu(); - } + if (!tsk->used_math) + init_fpu(tsk); + restore_fpu(tsk); set_thread_flag(TIF_USEDFPU); /* So we fnsave on switch_to() */ } diff -urN linux-2.5.8/include/asm-i386/i387.h linux/include/asm-i386/i387.h --- linux-2.5.8/include/asm-i386/i387.h Fri Apr 19 18:44:48 2002 +++ linux/include/asm-i386/i387.h Fri Apr 19 19:34:03 2002 @@ -17,7 +17,7 @@ #include #include -extern void init_fpu(void); +extern void init_fpu(struct task_struct *); /* * FPU lazy state save handling... */ --------------090405060502080603080707--