Re: repost: patch for 2.1.108 LDT problems
Wolfgang Walter (wolfgang.walter@stusta.mhn.de)
Wed, 8 Jul 1998 01:21:08 +0200
On Tue, Jul 07, 1998 at 05:47:49PM -0400, George wrote:
> On Tue, 7 Jul 1998, Alan Cox wrote:
>
> >> If you do, please make it a sysctl'able option. At least on my AMD-K6-PR2/200
> >> I have not experienced lockups/crashes yet.
> >
> >Interesting. Does this crash your K6 under 2.0.x ?
> >
> >On Mon, Jun 01, 1998 at 02:03:13PM +0200, Wolfgang Walter wrote:
> >
> >Here is how to reproduce it :
> >
> >$ cat a.s
> > .text
> > .align 4096 /* r1 */
> > .globl _start
> >_start:
> > movl _start, %edi /* S1 */
> > cmpb 0x80000000(%edi),%dl /* r2, S2 */
> > je nowhere /* r3 */
> > ret
> >$ as -o a.o a.s
> >$ ld -defsym nowhere=0xc0000000 a.o
> >$ ./a.out
> ><lockup. hard reset required>
> >
> >If so that indicates why we can't allow LDT usage by non root users on
> >AMD components
>
> I thought the conclusion previously was that (inadvertantly) 2.1.x prevents
> this problem already by extending the segment to cover all of virtual
> memory?
Hmm, the author of this little program was Benoit Poulot-Cazajous, and he had
some ideas why 2.1.43 fixed that. I think he thought that it because the
segment was extended and reducing it triggers the bug again. I think I'll
search his mail about that tomorrow.
Wolfgang Walter
>
> (Too bad I have an Intel or I'd check.)
>
> -George
>
>
> -
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