linux-kernel - Re: [PATCH] x86/KASLR: move aligning of minimal address to choose_random

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Message-ID: <20180104100308.GB7235@x1>
Date:   Thu, 4 Jan 2018 18:03:08 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Alexander Kuleshov <kuleshovmail@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Kees Cook <keescook@...omium.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/KASLR: move aligning of minimal address to
 choose_random_location()

On 01/04/18 at 03:54pm, Alexander Kuleshov wrote:
> we align minimal possible address during randomization to CONFIG_PHYSICAL_ALIGN
> two times: during getting of random physical address and virtual
> address (only for x86_64).
> 
> Let's move this to choose_random_location() to not duplicate code in
> find_random_virt_addr() and find_random_phys_addr().
> 
> Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
> ---
>  arch/x86/boot/compressed/kaslr.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 8199a6187251..8c93e399fdfd 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -673,9 +673,6 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
>  		return 0;
>  	}
>  
> -	/* Make sure minimum is aligned. */
> -	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
> -
>  	if (process_efi_entries(minimum, image_size))
>  		return slots_fetch_random();
>  
> @@ -688,8 +685,6 @@ static unsigned long find_random_virt_addr(unsigned long minimum,
>  {
>  	unsigned long slots, random_addr;
>  
> -	/* Make sure minimum is aligned. */
> -	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
>  	/* Align image_size for easy slot calculations. */
>  	image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
>  
> @@ -738,6 +733,9 @@ void choose_random_location(unsigned long input,
>  	 */
>  	min_addr = min(*output, 512UL << 20);
>  
> +	/* Make sure minimum is aligned. */
> +	min_addr = ALIGN(min_addr, CONFIG_PHYSICAL_ALIGN);

Hmm, the min_addr is passed to find_random_phys_addr(), but not to
find_random_virt_addr().

> +
>  	/* Walk available memory entries to find a random address. */
>  	random_addr = find_random_phys_addr(min_addr, output_size);
>  	if (!random_addr) {
> -- 
> 2.14.3
>