linux-kernel - Re: mmap syscall problem

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, 6 Jul 2009 16:16:11 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	michal.simek@...alogix.com
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	LTP <ltp-list@...ts.sourceforge.net>,
	John Williams <john.williams@...alogix.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	subrata@...ux.vnet.ibm.com
Subject: Re: mmap syscall problem

On Monday 06 July 2009, Michal Simek wrote:
> 
> > Not necessarily, even on platforms that manage aliases in hardware
> > mappings that violate the aliasing constraints can still result in
> > undefined behaviour, this really depends more on your cache controller
> > and MMU than anything else. I notice that microblaze sets SHMLBA to
> > PAGE_SIZE, you may want to see if this test still breaks after bumping it
> > up to something like PAGE_SIZE * 4.
> >   
> Yes, test still break - behavior is the same. I don't have accurate
> information about MMU unit
> but I will ask a question about. We are able to turn off cache
> controller directly in HW.

There may still be a problem with data being queued in some write
buffers that don't get flushed before reading back from another
address.

What happens in a simple user space program that mmaps the same
page to two addresses? Something like

#include <sys/mman.h>
#include <fcntl.h>
int main(void)
{
	int fd = open("existing-4k-file", O_RDWR);
	char *p1 = mmap(0, 4096, PROT_READ | PROT_WRITE,
				MAP_SHARED, fd, 0);
	char *p2 = mmap(p1 + 4096, 4096, PROT_READ | PROT_WRITE,
				MAP_SHARED | MAP_FIXED, fd, 0);

	*p1 = 0xaa; *p2 = 0x55;

	return *p1; /* returns 0xaa if broken, 0x55 if correct */
}

	Arnd <><
--
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/