-------- Original Message -------- From: [EMAIL PROTECTED] Wed Nov 7 06:14:01 2007 Return-Path: <[EMAIL PROTECTED]> X-Original-To: [EMAIL PROTECTED] Delivered-To: [EMAIL PROTECTED] Received: from localhost (mail.recluse.de [78.47.255.98]) by mail.recluse.de (Postfix) with ESMTP id B51FF392926 for <[EMAIL PROTECTED]>; Wed, 7 Nov 2007 06:14:01 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at recluse.de Received: from mail.recluse.de ([78.47.255.98]) by localhost (mail.recluse.de [78.47.255.98]) (amavisd-new, port 10024) with ESMTP id G2XieC59A2xV for <[EMAIL PROTECTED]>; Wed, 7 Nov 2007 06:14:00 +0100 (CET) Received: from sunset.davemloft.net (unknown [74.93.104.97]) by mail.recluse.de (Postfix) with ESMTP id 8373A392919 for <[EMAIL PROTECTED]>; Wed, 7 Nov 2007 06:13:58 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by sunset.davemloft.net (Postfix) with ESMTP id 1BEBEC8C526; Tue, 6 Nov 2007 21:13:57 -0800 (PST) Date: Tue, 06 Nov 2007 21:13:56 -0800 (PST) Message-Id: <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: Re: Fix for sparc64 cpu hangs. From: David Miller <[EMAIL PROTECTED]> In-Reply-To: <[EMAIL PROTECTED]> References: <[EMAIL PROTECTED]> X-Mailer: Mew version 5.2 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit
From: David Miller <[EMAIL PROTECTED]> Date: Tue, 06 Nov 2007 20:34:33 -0800 (PST) > [FUTEX]: Fix address computation in compat code. Sorry, I just noticed there is a second handle_futex_death() call in compat_exit_robust_list() which has the same address computation bug. Here is an updated patch: [FUTEX]: Fix address computation in compat code. compat_exit_robust_list() computes a pointer to the futex entry in userspace as follows: (void __user *)entry + futex_offset 'entry' is a 'struct robust_list __user *', and 'futex_offset' is a 'compat_long_t' (typically a 's32'). Things explode if the 32-bit sign bit is set in futex_offset. Type promotion sign extends futex_offset to a 64-bit value before adding it to 'entry'. This triggered a problem on sparc64 running 32-bit applications which would lock up a cpu looping forever in the fault handling for the userspace load in handle_futex_death(). Compat userspace runs with address masking (wherein the cpu zeros out the top 32-bits of every effective address given to a memory operation instruction) so the sparc64 fault handler accounts for this by zero'ing out the top 32-bits of the fault address too. Since the kernel properly uses the compat_uptr interfaces, kernel side accesses to compat userspace work too since they will only use addresses with the top 32-bit clear. Because of this compat futex layer bug we get into the following loop when executing the get_user() load near the top of handle_futex_death(): 1) load from address '0xfffffffff7f16bd8', FAULT 2) fault handler clears upper 32-bits, processes fault for address '0xf7f16bd8' which succeeds 3) goto #1 I want to thank Bernd Zeimetz, Josip Rodin, and Fabio Massimo Di Nitto for their tireless efforts helping me track down this bug. Signed-off-by: David S. Miller <[EMAIL PROTECTED]> diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c index 00b5726..1931457 100644 --- a/kernel/futex_compat.c +++ b/kernel/futex_compat.c @@ -30,6 +30,15 @@ fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, return 0; } +static void __user *futex_uaddr(struct robust_list *entry, + compat_long_t futex_offset) +{ + compat_uptr_t base = ptr_to_compat(entry); + void __user *uaddr = compat_ptr(base + futex_offset); + + return uaddr; +} + /* * Walk curr->robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. @@ -76,11 +85,13 @@ void compat_exit_robust_list(struct task_struct *curr) * A pending lock might already be on the list, so * dont process it twice: */ - if (entry != pending) - if (handle_futex_death((void __user *)entry + futex_offset, - curr, pi)) - return; + if (entry != pending) { + void __user *uaddr = futex_uaddr(entry, + futex_offset); + if (handle_futex_death(uaddr, curr, pi)) + return; + } if (rc) return; uentry = next_uentry; @@ -94,9 +105,11 @@ void compat_exit_robust_list(struct task_struct *curr) cond_resched(); } - if (pending) - handle_futex_death((void __user *)pending + futex_offset, - curr, pip); + if (pending) { + void __user *uaddr = futex_uaddr(pending, futex_offset); + + handle_futex_death(uaddr, curr, pip); + } } asmlinkage long -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]