linux-kernel - Re: [patch v2 4/4] ptrace: Add support for generic PTRACE_GETREGSET/PTRACE

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Message-ID: <4B73689F.5090407@zytor.com>
Date:	Wed, 10 Feb 2010 18:17:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <roland@...hat.com>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, hjl.tools@...il.com
Subject: Re: [patch v2 4/4] ptrace: Add support for generic	PTRACE_GETREGSET/PTRACE_SETREGSET

On 02/10/2010 11:12 AM, Roland McGrath wrote:
> 
> Since it's just two words, most places handling struct iovec seem to just
> use two get_user() calls, which is probably more efficient.
> 
> Also, here is where this function would need to be split in half for
> compat_ptrace_request() calls where it has to use struct compat_iovec.
> 
>> +	// I am not sure. Afaics it is OK to pass the
>> +	// size which is less than n * size. If iov_len
>> +	// is bigger, we can silently truncate it, or
>> +	// even write the correct value back.
> 
> Modifying iov_len to report how much we accessed seems good to me.  If we
> do that, we should certainly allow a larger size for get, so userland can
> just use a generic large buffer before even knowing the real size.  I'm not
> sure whether we should allow a smaller size, especially for set.  I could
> go either way.
> 

Allowing a larger size for get seems very sane.  Allowing a smaller size
would be ok iff we make sure we handle corner cases right (i.e. a
partially overwritten subregister.)

	-hpa
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