Re: [Patch 01/11] Introducing generic hardware breakpoint handlerinterfaces

[Alan Stern]

On Tue, 24 Mar 2009, K.Prasad wrote:

> > > Ok. Will do something like:
> > > return (va <= (TASK_SIZE - (hw_breakpoint_length * word_size)));
> > 
> > What is the purpose of word_size here?  The breakpoint length should be 
> > specified in bytes, not words.
> > 
> > Don't forget that that in arch_check_va_in_kernelspace() you need to 
> > check both for values that are too low and values that are too high 
> > (they overflow and wrap around back to a user address).
> > 
> 
> While I understand the user-space checking using the length of the HW
> Breakpoint, I don't really see how I can check for an upper-bound for
> kernel-space virtual addresses. Most usage in the kernel only checks for
> the address >= TASK_SIZE (while they check for add + len if the length
> of the memory is known). I will be glad to have any suggestions in this
> regard.

Isn't that exactly the check you need to implement?

	addr >= TASK_SIZE && (addr + len) >= TASK_SIZE,

or perhaps better,

	addr >= TASK_SIZE && (addr + len) >= addr.

In this case you _do_ know the length of the breakpoint.

Alan Stern

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