Re: [Fwd: TASK_SIZE is variable.]

Re: [Fwd: TASK_SIZE is variable.]

[Christoph Hellwig]

Content-Description: Forwarded message - TASK_SIZE is variable.
> Date: Tue, 25 Jan 2005 22:26:52 +0000
> From: David Woodhouse <dwmw2@infradead.org>
> Subject: TASK_SIZE is variable.
> To: linux-arch@vger.kernel.org
> X-Mailer: Evolution 2.0.2 (2.0.2-3.dwmw2.1) 
> 
> Bad things can happen if a 32-bit process is the last user of a 64-bit
> mm. TASK_SIZE isn't a constant, and we can end up clearing page tables
> only up to the 32-bit TASK_SIZE instead of all the way. We should
> probably double-check every instance of TASK_SIZE or USER_PTRS_PER_PGD
> for this kind of problem.

Or better get rid of TASK_SIZE completely.  Having something that looks
like a constant change depending on the user process is a bad idea.

> We should also double-check that MM_VM_SIZE() and other such things are
> correctly defined on all architectures. I already fixed ppc64 which let
> it stay as TASK_SIZE, and hence dependent on the _current_ context
> instead of the mm in the argument.
> 
> --- mm/mmap.c.orig	2005-01-25 22:23:02.030427272 +0000
> +++ mm/mmap.c	2005-01-25 22:23:55.627279312 +0000
> @@ -1612,8 +1612,8 @@ static void free_pgtables(struct mmu_gat
>  	unsigned long last = end + PGDIR_SIZE - 1;
>  	struct mm_struct *mm = tlb->mm;
>  
> -	if (last > TASK_SIZE || last < end)
> -		last = TASK_SIZE;
> +	if (last > MM_VM_SIZE(mm) || last < end)
> +		last = MM_VM_SIZE(mm);
>  
>  	if (!prev) {
>  		prev = mm->mmap;
> @@ -1996,7 +1996,7 @@ void exit_mmap(struct mm_struct *mm)
>  	vm_unacct_memory(nr_accounted);
>  	BUG_ON(mm->map_count);	/* This is just debugging */
>  	clear_page_range(tlb, FIRST_USER_PGD_NR * PGDIR_SIZE,
> -			(TASK_SIZE + PGDIR_SIZE - 1) & PGDIR_MASK);
> +			(MM_VM_SIZE(mm) + PGDIR_SIZE - 1) & PGDIR_MASK);
>  	
>  	tlb_finish_mmu(tlb, 0, MM_VM_SIZE(mm));
>  
> 
> -- 
> dwmw2

Re: [Fwd: TASK_SIZE is variable.]

[David Woodhouse]

On Tue, 2005-01-25 at 22:46 +0000, Christoph Hellwig wrote:
> > Bad things can happen if a 32-bit process is the last user of a 64-bit
> > mm. TASK_SIZE isn't a constant, and we can end up clearing page tables
> > only up to the 32-bit TASK_SIZE instead of all the way. We should
> > probably double-check every instance of TASK_SIZE or USER_PTRS_PER_PGD
> > for this kind of problem.
> 
> Or better get rid of TASK_SIZE completely.  Having something that looks
> like a constant change depending on the user process is a bad idea.

Yeah, that's possibly a sane plan.

-- 
dwmw2