linux-kernel - Re: [PATCH v2 0/8] clean up vdso-layout.lds.S

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Message-Id: <20090616103445.A3008D56E@magilla.sf.frob.com>
Date:	Tue, 16 Jun 2009 03:34:45 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Petr Tesarik <ptesarik@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v2 0/8] clean up vdso-layout.lds.S

> Upfront, thank you very much for reviewing the series, Roland!

I'm glad to help.

> And there currently isn't one. But the writability of the vDSO is a bit
> more complicated. True, the VMA is initially mapped read-only, but it is
> possible to make it writable using mprotect(). 

Except for CONFIG_COMPAT_VDSO on X86_32.

> You may also set an
> INT3-style breakpoint in the vDSO area. So, it's all about policy. If
> there were any demand to make the vDSO writable, it could be done with a
> trivial patch.

There's a big difference between "writable" and "might be written".

> If we do not _WANT_ to make it writable, then we can simply add .data
> and .bss to .broken.

That is the correct thing to do.

> Yes, all .rel* sections should be in .broken, I guess.

You can toss an "void *x = &x;" into the vdso sources to verify that this
setup makes that explode gracefully.

> This was an attempt to discard .note.GNU-stack, which is what the
> default linker script does, but it appears that all .note.GNU-stack
> sections are zero-size, so this change does not make any difference.

Indeed it does not.


Thanks,
Roland
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