linux-kernel - Re: [PATCH 14(16] pramfs: memory protection

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]

Date:	Mon, 11 Oct 2010 19:32:10 +0200
From:	Marco Stornelli <marco.stornelli@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Tim Bird <tim.bird@...sony.com>, linux-mm@...ck.org
Subject: Re: [PATCH 14(16] pramfs: memory protection

Il 10/10/2010 18:46, Andi Kleen ha scritto:
> This won't work at all on x86 because you don't handle large 
> pages.
> 
> And it doesn't work on x86-64 because the first 2GB are double
> mapped (direct and kernel text mapping)
> 
> Thirdly I expect it won't either on architectures that map
> the direct mapping with special registers (like IA64 or MIPS)

Andi, what do you think to use the already implemented follow_pte
instead? 

int writeable_kernel_pte_range(unsigned long address, unsigned long size,
							      unsigned int rw)
{

	unsigned long addr = address & PAGE_MASK;
	unsigned long end = address + size;
	unsigned long start = addr;
	int ret = -EINVAL;
	pte_t *ptep, pte;
	spinlock_t *lock = &init_mm.page_table_lock;

	do {
		ret = follow_pte(&init_mm, addr, &ptep, &lock);
		if (ret)
			goto out;
		pte = *ptep;
		if (pte_present(pte)) {
			  pte = rw ? pte_mkwrite(pte) : pte_wrprotect(pte);
			  *ptep = pte;
		}
		pte_unmap_unlock(ptep, lock);
		addr += PAGE_SIZE;
	} while (addr && (addr < end));

	ret = 0;

out:
	flush_tlb_kernel_range(start, end);
	return ret;
}


> 
> I'm not sure this is very useful anyways. It doesn't protect
> against stray DMA and it doesn't protect against writes through
> broken user PTEs.
> 
> -Andi
> 

It's a way to have more protection against kernel bug, for a 
in-memory fs can be important. However this option can be 
enabled/disabled at fs level.

Marco
--
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/