Re: Compat 32-bit syscall entry from 64-bit task!?

[H. Peter Anvin]

On 02/08/2012 10:03 PM, Indan Zupancic wrote:
> You can check the syscall instruction itself, either before it's executed
> or afterwards by checking the IP. Though that's trickier, because the
> kernel points the IP to just after int80 for a sysenter call, so you have
> to check if there's a sysenter nearby too.

No, that's a total nightmare.  FAIL.

> But the kernel is actually changing the registers, so why hide that?
>
> I mean, once user space is aware that the kernel may do swizzling, is there
> any actual problem left? Because this sounds like user space was trying to
> be clever, but got it wrong. E.g. it knew the kernel was entered not via
> int80, but then got confused because of the swizzling.

I would be great if we didn't have an existing compatibility problem. 
As it is we can't get rid of it easily.

	-hpa

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