Re: [patch 1/1] make PROT_WRITE imply PROT_READ

Alan Cox
2006-09-17T20:51:54Z

Ar Sul, 2006-09-17 am 13:24 -0700, ysgrifennodd Chris Wedgwood:
> On Thu, Sep 14, 2006 at 06:39:47PM -0700, akpm@osdl.org wrote:
>
> > Make PROT_WRITE imply PROT_READ for a number of architectures which
> > don't support write only in hardware.
>
> Why don't we WARN where PROT_WRITE is used w/o PROT_READ? Do
> non-trivial or non-contrived applications really use PROT_WRITE and
> assume reads are OK?

Unfortunately yes. This was discovered in the real world.

> It seems once we do this there will be little or no chance of ever
> doing write-only mappings should we want to in the future using this
> mechanism.

Executable types already let us handle that, or as you suggest but the
other way around you add PROT_REALLYLIKEWRITEONLYOK as a new mmap type
(and as PROT_WRITE) for a new binary format later if the CPU ever
supports it. Frankly I think the odds of Intel cpus growing write-only
are remote....

Alan