From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <schwab@suse.de>
Received: from mx1.suse.de (ns1.suse.de [195.135.220.2])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(Client CN "mx1.suse.de", Issuer "CAcert Class 3 Root" (verified OK))
	by ozlabs.org (Postfix) with ESMTPS id 808FADDDEC
	for <linuxppc-dev@ozlabs.org>; Thu,  6 Nov 2008 21:49:06 +1100 (EST)
From: Andreas Schwab <schwab@suse.de>
To: Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] Fix msr check in compat_sys_swapcontext
References: <jeprlabbi6.fsf@sykes.suse.de>
	<18706.16317.759662.855430@cargo.ozlabs.ibm.com>
	<jey6zx9piz.fsf@sykes.suse.de>
	<18706.51381.987014.370948@cargo.ozlabs.ibm.com>
Date: Thu, 06 Nov 2008 11:49:00 +0100
In-Reply-To: <18706.51381.987014.370948@cargo.ozlabs.ibm.com> (Paul
	Mackerras's message of "Thu, 6 Nov 2008 21:36:37 +1100")
Message-ID: <jek5bh9lk3.fsf@sykes.suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.ozlabs.org>
List-Unsubscribe: <https://ozlabs.org/mailman/options/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=unsubscribe>
List-Archive: <http://ozlabs.org/pipermail/linuxppc-dev>
List-Post: <mailto:linuxppc-dev@ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@ozlabs.org?subject=help>
List-Subscribe: <https://ozlabs.org/mailman/listinfo/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=subscribe>

Paul Mackerras <paulus@samba.org> writes:

> Andreas Schwab writes:
>
>> Paul Mackerras <paulus@samba.org> writes:
>> 
>> > we need to use get_user, not __get_user, since we haven't done an
>> > access_ok() check on the address.
>> 
>> The address is always ok since its a compat pointer, see do_setcontext.
>
> OK, since it's inside a CONFIG_PPC64 block.  I'll add a paragraph to
> the patch description pointing that out.

How about this:

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index a6a4310..b13abf3 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -941,9 +941,21 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
 #ifdef CONFIG_PPC64
 	unsigned long new_msr = 0;
 
-	if (new_ctx &&
-	    get_user(new_msr, &new_ctx->uc_mcontext.mc_gregs[PT_MSR]))
-		return -EFAULT;
+	if (new_ctx) {
+		struct mcontext __user *mcp;
+		u32 cmcp;
+
+		/*
+		 * Get pointer to the real mcontext.  No need for
+		 * access_ok since we are dealing with compat
+		 * pointers.
+		 */
+		if (__get_user(cmcp, &new_ctx->uc_regs))
+			return -EFAULT;
+		mcp = (struct mcontext __user *)(u64)cmcp;
+		if (__get_user(new_msr, &mcp->mc_gregs[PT_MSR]))
+			return -EFAULT;
+	}
 	/*
 	 * Check that the context is not smaller than the original
 	 * size (with VMX but without VSX)

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."