linux-kernel - Re: [PATCH 1/2] fs, elf: drop MAP_FIXED usage from elf

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Date:   Tue, 17 Oct 2017 10:56:43 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     James Hogan <james.hogan@...s.com>
Cc:     Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Al Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Baoquan He <bhe@...hat.com>,
        linux-metag@...r.kernel.org
Subject: Re: [PATCH 1/2] fs, elf: drop MAP_FIXED usage from elf_map

On Tue 17-10-17 09:35:57, James Hogan wrote:
> On Tue, Oct 17, 2017 at 09:37:48AM +0200, Michal Hocko wrote:
[...]
> > This would be something like. I wanted to share elf_vm_mmap but didn't
> > find a proper place to not cause include dependency hell so I balied out
> > to c&p.
> > ---
> > diff --git a/arch/metag/kernel/process.c b/arch/metag/kernel/process.c
> > index c4606ce743d2..b20596b4c4c2 100644
> > --- a/arch/metag/kernel/process.c
> > +++ b/arch/metag/kernel/process.c
> > @@ -378,6 +378,29 @@ int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu)
> >  
> >  #define BAD_ADDR(x) ((unsigned long)(x) >= TASK_SIZE)
> >  
> > +static unsigned long elf_vm_mmap(struct file *filep, unsigned long addr,
> > +		unsigned long size, int prot, int type, unsigned long off)
> > +{
> > +	unsigned long map_addr;
> > +
> > +	/*
> > +	 * If caller requests the mapping at a specific place, make sure we fail
> > +	 * rather than potentially clobber an existing mapping which can have
> > +	 * security consequences (e.g. smash over the stack area).
> > +	 */
> > +	map_addr = vm_mmap(filep, addr, size, prot, type & ~MAP_FIXED, off);
> > +	if (BAD_ADDR(map_addr))
> > +		return map_addr;
> > +
> > +	if ((type & MAP_FIXED) && map_addr != addr) {
> > +		pr_info("Uhuuh, elf segement at %p requested but the memory is mapped already\n",
> > +				(void*)addr);
> > +		return -EAGAIN;
> > +	}
> > +
> > +	return map_addr;
> > +}
> > +
> >  unsigned long __metag_elf_map(struct file *filep, unsigned long addr,
> >  			      struct elf_phdr *eppnt, int prot, int type,
> >  			      unsigned long total_size)
> > @@ -410,11 +433,11 @@ unsigned long __metag_elf_map(struct file *filep, unsigned long addr,
> >  	*/
> >  	if (total_size) {
> >  		total_size = ELF_PAGEALIGN(total_size);
> > -		map_addr = vm_mmap(filep, addr, total_size, prot, type, off);
> > +		map_addr = elf_vm_mmap(filep, addr, total_size, prot, type, off);
> >  		if (!BAD_ADDR(map_addr))
> >  			vm_munmap(map_addr+size, total_size-size);
> >  	} else
> > -		map_addr = vm_mmap(filep, addr, size, prot, type, off);
> > +		map_addr = elf_vm_mmap(filep, addr, size, prot, type, off);
> >  
> >  	if (!BAD_ADDR(map_addr) && tcm_tag != TCM_INVALID_TAG) {
> >  		struct tcm_allocation *tcm;
> 
> Yeh that looks reasonable to me.

Thanks for double checking. I will make sure to CC you when reposting
the patch after other concerns sort out.

-- 
Michal Hocko
SUSE Labs