linux-kernel - Re: [PATCH] x86, efi: Don't recursively acquire rtc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <4E3A17BD0200007800073FC5@nat28.tlf.novell.com>
Date:	Thu, 04 Aug 2011 03:53:32 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<matt@...sole-pimps.org>, <linux-kernel@...r.kernel.org>
Cc:	<fenghua.yu@...el.com>, <tony.luck@...el.com>,
	<hpa@...ux.intel.com>, <matt.fleming@...ux.intel.com>,
	<mjg@...hat.com>, <a.zummo@...ertech.it>
Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock

>>> Matt Fleming 08/03/11 11:04 PM >>> 
>From: Matt Fleming 
>
>A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86: 
>Serialize EFI time accesses on rtc_lock") because efi_get_time() and 
>friends can be called with rtc_lock already held by 
>read_persistent_time(), e.g. 
>
>timekeeping_init() 
>read_persistent_clock() <-- acquire rtc_lock 
>efi_get_time() 
>phys_efi_get_time() <-- acquire rtc_lock 
>
>Move the locking up into the caller of efi.get_time() and provide some 
>wrappers for use in other parts of the kernel instead of calling 
>efi.get_time(), etc directly. This way we can hide the rtc_lock dance 
>inside of arch/x86. 

Seems the wrong approach to me: The call happening with the lock held
is the wrong part imo, and hence the fix ought to be to drop the lock
there.

Jan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/