Re: [RFC][PATCH] linux-2.6.2-rc2_vsyscall-gtod_B1.patch

Andrea Arcangeli
2004-02-03T19:43:50Z

On Tue, Feb 03, 2004 at 06:23:10PM +0000, Jamie Lokier wrote:
> Andrea Arcangeli wrote:
> > vsyscalls will never execute anything like execve. They can at most
> > modify userspace memory a fixed address, so if the userspace isn't
> > fixed, then nothing can be done with a vsyscall.
>
> Are we talking about the same x86_64?

I did, I don't think it worth to backport to i386 btw.

>
> I see this in arch/x86_64/vsyscall.S:
>
> __kernel_vsyscall:
> .LSTART_vsyscall:
> push %ebp
> .Lpush_ebp:
> movl %ecx, %ebp
> syscall
>
> Is that page not mapped into userspace?

this code wasn't there last time I worked on it, it's not in 2.4 either.
I assume it's mapped in userspace, but I'm unsure why it's necessary. I
need to think more about it to understand why such code is there and how
can it be removed. I was taking about the .c file not this new .S one.