linux-kernel - Re: [PATCH] x86: Fix /proc/mtrr with base/size more than 44bits

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <51BA2FF4.6000604@zytor.com>
Date:	Thu, 13 Jun 2013 13:47:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86: Fix /proc/mtrr with base/size more than 44bits

On 06/13/2013 11:53 AM, Yinghai Lu wrote:
>  
> -	if (base & size_or_mask || size & size_or_mask) {
> +	if (base >> (boot_cpu_data.x86_phys_bits - PAGE_SHIFT) ||
> +	    base > (base + size) ||
> +	    (base + size - 1) >> (boot_cpu_data.x86_phys_bits - PAGE_SHIFT)) {
>  		pr_warning("mtrr: base or size exceeds the MTRR width\n");
>  		return -EINVAL;
>  	}

Most of this patch looks good as far as being a minimal patch, but I'm
really confused about this bit.  Could you explain the reason for why
the original doesn't work?  (To be fair: I am not even sure the original
does anything useful so it could just be a "this is just too broken to
live" kind of thing.)

The first and third clause of the test can be simplified, however:

	(base | (base + size - 1)) >> (boot_cpu_data.x86_phys_bits - PAGE_SHIFT)

... although it would be cleaner to put boot_cpu_data.x86_phys_bits -
PAGE_SHIFT into a variable.

A lot of the mask_hi/mask_lo stuff should just get removed by using
rdmsrl/wrmsrl, but that is not stable material obviously.

	-hpa

--
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/