linux-kernel - Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the immovable memory

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]

Message-ID: <20180827070109.GD1748@MiWiFi-R3L-srv>
Date:   Mon, 27 Aug 2018 15:01:09 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, n-horiguchi@...jp.nec.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com,
        douly.fnst@...fujitsu.com
Subject: Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the
 immovable memory

On 08/27/18 at 02:28pm, Chao Fan wrote:
> >Is it possible to take num_immovable_mem definition out from #ifdef
> >CONFIG_MEMORY_HOTREMOVE block and check it here like below? This way,
> >one level of indentation can be reduced in the for loop, and code is
> >more readable.
> >
> 
> I think there is a mistake.
> 
> The logical is:
> if (#ifdef CONFIG_MEMORY_HOTREMOVE) && (num_immovable_mem > 0)
> 	then A;
> else
> 	then B;
> 
> But below is:
> if (num_immovable_mem > 0)
> 	then B;
> else if (#ifdef CONFIG_MEMORY_HOTREMOVE)
> 	then A;
> else
> 	nothing;
> 
> The precondition of the loop is (num_immovable_mem > 0), because
> there is only one condition that we need go the A code:
> CONFIG_MEMORY_HOTREMOVE is defined, and memory information in srat
> found.


Yes, we are saying the same thing. if num_immovable_mem == 0, it covers
all the cases you listed at below. Here I assume you have taken
num_immovable_mem definition out.

#ifdef CONFIG_MEMORY_HOTREMOVE
/* Store the immovable memory regions */
static struct mem_vector immovable_mem[MAX_NUMNODES*2];
#endif

/* Store the amount of immovable memory regions */
static int num_immovable_mem;

> 
> But there is many conditions we go the B code:
> 1. CONFIG_MEMORY_HOTREMOVE is not defined.
> 2. CONFIG_MEMORY_HOTREMOVE defined, but we didn't get the right acpi tables
> 3. CONFIG_MEMORY_HOTREMOVE defined, or there is only one node in this machine.
> 
> Yes, the code is hard to read, but you have changed the logical, there
> is a compromise method, I don't know whether is better:
> 
> #ifdef CONFIG_MEMORY_HOTREMOVE
> 	if (num_immovable_mem == 0)
> 		goto B;
> 
> 	for (i = 0; i < num_immovable_mem; i++) {
> 		...
> 	}
> #endif
> 
> B:
> 	slots_count(region, minimum, image_size);
> 	
> 	if (slot_area_index == MAX_SLOT_AREA) {
> 		debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
> 		return 1;
> 	}
> 	return 0;
> 	
> 
> >
> >static bool process_mem_region(struct mem_vector *region,
> >			       unsigned long long minimum,
> >			       unsigned long long image_size)
> >{
> >
> >	/*
> >	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
> >	 * walk all the regions, so use region directely.
> >	 */
> >	if (num_immovable_mem > 0) {
> >		slots_count(region, minimum, image_size);
> >		
> >		if (slot_area_index == MAX_SLOT_AREA) {
> >			debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
> >			return 1;
> >		}
> >		return 0;
> >	}
> >
> >#ifdef CONFIG_MEMORY_HOTREMOVE
> >	for (i = 0; i < num_immovable_mem; i++) {
> >		...
> >	}
> >#endif
> >}
> >
> 
>