linux-kernel - Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing a privcmd call

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

Date:	Fri, 11 Sep 2015 18:09:21 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<xen-devel@...ts.xenproject.org>,
	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	Riku Voipio <riku.voipio@...aro.org>
Subject: Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing
 a privcmd call

On 11/09/15 18:00, Russell King - ARM Linux wrote:
> On Fri, Sep 11, 2015 at 05:25:59PM +0100, Julien Grall wrote:
>> +	/*
>> +	 * Privcmd calls are issued by the userspace. We need to allow the
>> +	 * kernel to access the userspace memory before issuing the hypercall.
>> +	 */
>> +	uaccess_enable r4
>> +
>> +	/* r4 is loaded now as we use it as scratch register before */
>>  	ldr r4, [sp, #4]
> 
> As I mentioned in one of my previous mails, "ip" should be safe to use
> here - it's a caller-corrupted register, just like r0-r3 and lr.  So,
> you could do:
> 
> 	ldr r4, [sp, #4]
> +	uaccess_enable ip

The register ip (aka r12) is used to store the hypercall number.
The easiest one, without much changes, was r4.

> which fractionally tightens the window.
> 
> However, there's nothing actually wrong with your version - there's no
> way we could've got this far with sp pointing at userspace.
> 
> I'm happy with either version, so:
> 
> Acked-by: Russell King <rmk+kernel@....linux.org.uk>

Thank you!

> 
> How do you want to handle the patch?  I already have some other uaccess
> fixes queued up to send to Linus before the merge window closes.

I was thinking to ask Stefano to carry it in Xen tree. But I don't mind
if it goes with your tree.

Regards,

-- 
Julien Grall
--
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/