linux-kernel - Re: [uClinux-dev] Re: [PATCH] FDPIC: respect PT_GNU_STACK exec markings when creating NOMMU stack

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Message-ID: <16680.1259863084@redhat.com>
Date:	Thu, 03 Dec 2009 17:58:04 +0000
From:	David Howells <dhowells@...hat.com>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	Greg Ungerer <gerg@...inux.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	David McCullough <davidm@...pgear.com>,
	uClinux development list <uclinux-dev@...inux.org>
Subject: Re: [uClinux-dev] Re: [PATCH] FDPIC: respect PT_GNU_STACK exec markings when creating NOMMU stack

Mike Frysinger <vapier.adi@...il.com> wrote:

> i have seen a few apps use brk()/sbrk() to query the size of things (like
> e2fsprogs)

We do actually record the size of the brk segment, so maybe we could icache
flush brk as it is increased (if it is increased):

	diff --git a/mm/nommu.c b/mm/nommu.c
	index 3754b16..2ea823d 100644
	--- a/mm/nommu.c
	+++ b/mm/nommu.c
	@@ -432,6 +432,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
		/*
		 * Ok, looks good - let it rip.
		 */
	+	flush_icache_range(mm->brk, brk);
		return mm->brk = brk;
	 }

It might also be worth making the availability of brk() a config option under
NOMMU.

> > Probably VM_DATA_DEFAULT_FLAGS should not include VM_EXEC for either
> > Blackfin or FRV, but it may be required for SH.  The if-statement that
> > calls elf_read_implies_exec() will be optimised away unless the arch
> > specifically sets it (which none of FRV, Blackfin or SH do).
> 
> while true, wont the later personality test (in VM_DATA_DEFAULT_FLAGS)
> be left there ?  guess it's not that big of a deal.

I think we could justify altering FRV and Blackfin to get rid of that test,
since we don't make use of read-implies-exec in those arches, but I think that
should be a separate patch.

David
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