Messages in this thread | | | Date | Mon, 23 Mar 2009 17:20:27 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [Patch 01/11] Introducing generic hardware breakpoint handler interfaces |
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On Tue, 24 Mar 2009, K.Prasad wrote:
> > 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 > > > > Aren't we just checking if len is a positive number through the above > checks? The validation checks in the patchset should take care of > negative lengths. Or am I missing something?
Well, 0x60000000 is a positive number, and 0xd0000000 is >= TASK_SIZE. But their sum is 0x30000000, which lies in userspace. In other words, you are missing the possibility that the addition might overflow and wrap around.
> I thought you wanted the code to check for an upper sane limit for addr > in kernel-space, say something like this: > > TASK_SIZE <= addr <= (Upper limit for Kernel Virtual Address)
No, the test should be
TASK_SIZE <= addr <= addr + (len-1) <= (Upper limit for Kernel VA)
By the way, is TASK_SIZE the correct lower bound for kernel virtual addresses on x86-64?
> When I referred to 'len' in my previous mail, it meant the length > of the kernel virtual memory area (which can be used to find the upper > bound).
Oh, sorry, I misunderstood. Isn't that limit always 0xffffffff on x86-32?
Alan Stern
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