linux-kernel - RE: [PATCH v2] binfmt_elf: Fix PIE execution with randomization disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled)

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Date:	Mon, 3 Oct 2011 09:02:47 -0700
From:	"Lu, Hongjiu" <hongjiu.lu@...el.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Jiri Kosina <jkosina@...e.cz>
CC:	Josh Boyer <jwboyer@...hat.com>, Andrew Morton <akpm00@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <rmk@....linux.org.uk>
Subject: RE: [PATCH v2] binfmt_elf: Fix PIE execution with randomization
 disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with
 randomization disabled)

Why not

#if defined(CONFIG_X86) || defined(CONFIG_ARM)
#define CHECK_PF_RANDOMIZE 1
#else
#define CHECK_PF_RANDOMIZE 0
#endif
			if (CHECK_PF_RANDOMIZE && (current->flags & PF_RANDOMIZE))
				load_bias = 0;
			else
				load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);

H.J.

> -----Original Message-----
> From: Nicolas Pitre [mailto:nicolas.pitre@...aro.org]
> Sent: Monday, October 03, 2011 8:56 AM
> To: Jiri Kosina
> Cc: Josh Boyer; Andrew Morton; Ingo Molnar; Lu, Hongjiu; linux-
> kernel@...r.kernel.org; Andrew Morton; Russell King
> Subject: Re: [PATCH v2] binfmt_elf: Fix PIE execution with randomization
> disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization
> disabled)
> 
> On Mon, 3 Oct 2011, Jiri Kosina wrote:
> 
> > How about the patch below instead? It survives my testing, and I believe
> > it handles both cases properly.
> >
> > Confirmation from the original bug reporter would obviously be a nice
> > bonus too :)
> >
> >
> >
> >
> > From: Jiri Kosina <jkosina@...e.cz>
> > Subject: [PATCH] binfmt_elf: fix PIE execution with randomization disabled
> >
> > The case of address space randomization being disabled in runtime through
> > randomize_va_space sysctl is not treated properly in load_elf_binary(),
> > resulting in SIGKILL coming at exec() time for certain PIE-linked binaries
> > in case the randomization has been disabled at runtime prior to calling
> > exec().
> >
> > Handle the randomize_va_space == 0 case the same way as if we were not
> > supporting .text randomization at all.
> >
> > Based on original patch by H.J. Lu <hongjiu.lu@...el.com> and
> > Josh Boyer <jwboyer@...hat.com>
> >
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Jiri Kosina <jkosina@...e.cz>
> > Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
> > Cc: Russell King <rmk@....linux.org.uk>
> > Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> 
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>
> 
> However I'd suggest a change to deal with style issues:
> 
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index dd0fdfc..bb11fe4 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -795,7 +795,10 @@ static int load_elf_binary(struct linux_binprm *bprm,
> struct pt_regs *regs)
> >  			 * might try to exec.  This is because the brk will
> >  			 * follow the loader, and is not movable.  */
> >  #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> > -			load_bias = 0;
> > +			if (current->flags & PF_RANDOMIZE)
> > +				load_bias = 0;
> > +			else
> > +				load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> >  #else
> >  			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> >  #endif
> 
> What about this instead, saving 3 lines out of 8:
> 
> 			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> 			if (current->flags & PF_RANDOMIZE)
> 				load_bias = 0;
> #endif
> 
> 
> ?
> 
> 
> Nicolas
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