Re: 4.4.-rc5: lguest causes ugly warn on: 5 W+X pages found

[Pavel Machek]

Hi!

> > Rusty, does the switcher need to be W+X?
> >
> > And yes, I have lguest enabled, not sure why. 
> 
> No.  The layout is "<text page> <per-cpu-stack-pages>..." and I lazily
> did that as a single
>         map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages);
> 
> This boots, does it solve the problem?

Let me see. Note that I'm not actually using lguest.

git complains about trailing whitespace in the patch.

Otherwise... yes, this helps. "no W+X pages found".

Tested-by: Pavel Machek <pavel@xxxxxx>

Thanks,
								Pavel

> Reported-by: Pavel Machek <pavel@xxxxxx>
> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> 
> diff --git a/arch/x86/include/asm/lguest.h b/arch/x86/include/asm/lguest.h
> index 3bbc07a57a31..73d0c9b92087 100644
> --- a/arch/x86/include/asm/lguest.h
> +++ b/arch/x86/include/asm/lguest.h
> @@ -12,7 +12,9 @@
>  #define GUEST_PL 1
>  
>  /* Page for Switcher text itself, then two pages per cpu */
> -#define TOTAL_SWITCHER_PAGES (1 + 2 * nr_cpu_ids)
> +#define SWITCHER_TEXT_PAGES (1)
> +#define SWITCHER_STACK_PAGES (2 * nr_cpu_ids)
> +#define TOTAL_SWITCHER_PAGES (SWITCHER_TEXT_PAGES + SWITCHER_STACK_PAGES)
>  
>  /* Where we map the Switcher, in both Host and Guest. */
>  extern unsigned long switcher_addr;
> diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
> index 312ffd3d0017..021915baef35 100644
> --- a/drivers/lguest/core.c
> +++ b/drivers/lguest/core.c
> @@ -22,7 +22,8 @@
>  
>  unsigned long switcher_addr;
>  struct page **lg_switcher_pages;
> -static struct vm_struct *switcher_vma;
> +static struct vm_struct *switcher_text_vma;
> +static struct vm_struct *switcher_stacks_vma;
>  
>  /* This One Big lock protects all inter-guest data structures. */
>  DEFINE_MUTEX(lguest_lock);
> @@ -83,54 +84,80 @@ static __init int map_switcher(void)
>  	}
>  
>  	/*
> +	 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
> +	 * It goes in the first page, which we map in momentarily.
> +	 */
> +	memcpy(kmap(lg_switcher_pages[0]), start_switcher_text,
> +	       end_switcher_text - start_switcher_text);
> +	kunmap(lg_switcher_pages[0]);
> +
> +	/*
>  	 * We place the Switcher underneath the fixmap area, which is the
>  	 * highest virtual address we can get.  This is important, since we
>  	 * tell the Guest it can't access this memory, so we want its ceiling
>  	 * as high as possible.
>  	 */
> -	switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
> +	switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE;
>  
>  	/*
> -	 * Now we reserve the "virtual memory area" we want.  We might
> -	 * not get it in theory, but in practice it's worked so far.
> -	 * The end address needs +1 because __get_vm_area allocates an
> -	 * extra guard page, so we need space for that.
> +	 * Now we reserve the "virtual memory area"s we want.  We might
> +	 * not get them in theory, but in practice it's worked so far.
> +	 *
> +	 * We want the switcher text to be read-only and executable, and
> +	 * the stacks to be read-write and non-executable.
>  	 */
> -	switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
> -				     VM_ALLOC, switcher_addr, switcher_addr
> -				     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
> -	if (!switcher_vma) {
> +	switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC|VM_NO_GUARD,
> +					  switcher_addr,
> +					  switcher_addr + PAGE_SIZE);
> +
> +	if (!switcher_text_vma) {
>  		err = -ENOMEM;
>  		printk("lguest: could not map switcher pages high\n");
>  		goto free_pages;
>  	}
>  
> +	switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE,
> +					    VM_ALLOC|VM_NO_GUARD,
> +					    switcher_addr + PAGE_SIZE,
> +					    switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE);
> +	if (!switcher_stacks_vma) {
> +		err = -ENOMEM;
> +		printk("lguest: could not map switcher pages high\n");
> +		goto free_text_vma;
> +	}
> +
>  	/*
>  	 * This code actually sets up the pages we've allocated to appear at
>  	 * switcher_addr.  map_vm_area() takes the vma we allocated above, the
> -	 * kind of pages we're mapping (kernel pages), and a pointer to our
> -	 * array of struct pages.
> +	 * kind of pages we're mapping (kernel text pages and kernel writable
> +	 * pages respectively), and a pointer to our array of struct pages.
>  	 */
> -	err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages);
> +	err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages);
> +	if (err) {
> +		printk("lguest: text map_vm_area failed: %i\n", err);
> +		goto free_vmas;
> +	}
> +
> +	err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL,
> +			  lg_switcher_pages + SWITCHER_TEXT_PAGES);
>  	if (err) {
> -		printk("lguest: map_vm_area failed: %i\n", err);
> -		goto free_vma;
> +		printk("lguest: stacks map_vm_area failed: %i\n", err);
> +		goto free_vmas;
>  	}
>  
>  	/*
>  	 * Now the Switcher is mapped at the right address, we can't fail!
> -	 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
>  	 */
> -	memcpy(switcher_vma->addr, start_switcher_text,
> -	       end_switcher_text - start_switcher_text);
> -
>  	printk(KERN_INFO "lguest: mapped switcher at %p\n",
> -	       switcher_vma->addr);
> +	       switcher_text_vma->addr);
>  	/* And we succeeded... */
>  	return 0;
>  
> -free_vma:
> -	vunmap(switcher_vma->addr);
> +free_vmas:
> +	/* Undoes map_vm_area and __get_vm_area */ 
> +	vunmap(switcher_stacks_vma->addr);
> +free_text_vma:
> +	vunmap(switcher_text_vma->addr);
>  free_pages:
>  	i = TOTAL_SWITCHER_PAGES;
>  free_some_pages:
> @@ -148,7 +175,8 @@ static void unmap_switcher(void)
>  	unsigned int i;
>  
>  	/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
> -	vunmap(switcher_vma->addr);
> +	vunmap(switcher_text_vma->addr);
> +	vunmap(switcher_stacks_vma->addr);
>  	/* Now we just need to free the pages we copied the switcher into */
>  	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
>  		__free_pages(lg_switcher_pages[i], 0);

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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