Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi_nochk for besteffort copy

[Andy Lutomirski]

On 07/22/2012 05:14 AM, Jiri Olsa wrote:
> Adding copy_from_user_nmi_nochk that provides the best effort
> copy regardless the requesting size crossing the task boundary.
> 
> This is going to be useful for stack dump we need in post
> DWARF CFI based unwind, where we have predefined size of
> the user stack to dump, and we need to store the most of
> the requested dump size, regardless this size is crossing
> the task boundary.

Huh?  This is a TASK_SIZE check, which makes sure that the request
doesn't cross into kernel land.  Otherwise userspace could presumably
read kernel memory by setting bogus values of sp.

--Andy
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