linux-kernel - Re: [PATCH 1/2] mm: vmalloc: Avoid a double lookup of freed VA in a tree

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y6ICwLwk3tPdZIqS@pc636>
Date:   Tue, 20 Dec 2022 19:45:20 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 1/2] mm: vmalloc: Avoid a double lookup of freed VA in a
 tree

On Tue, Dec 20, 2022 at 07:27:03PM +0100, Uladzislau Rezki (Sony) wrote:
> When a VA is freed over a main path, for example by invoking
> the vfree() function, a tree is accessed two times what is odd:
> 
> vfree():
>   __vunmap()
>     __find_vmap_area()
>   vm_remove_mappings()
>     remove_vm_area()
>       __find_vmap_area()
> 
> __find_vmap_area() are called two times. Fix it by introducing
> a find_unlink_vmap_area() helper that finds and un-links a VA
> from a tree.
> 
> Performance test results on a single CPU:
> 
> - fix_size_alloc_test       loops: 1000000 avg: 476847   usec
> - full_fit_alloc_test       loops: 1000000 avg: 806746   usec
> - long_busy_list_alloc_test loops: 1000000 avg: 13552093 usec
> - random_size_alloc_test    loops: 1000000 avg: 7441322  usec
> - fix_align_alloc_test      loops: 1000000 avg: 1411132  usec
> All test took worker0=87650866284 cycles
> 
> - fix_size_alloc_test       loops: 1000000 avg: 490713   usec
> - full_fit_alloc_test       loops: 1000000 avg: 579162   usec
> - long_busy_list_alloc_test loops: 1000000 avg: 10485448 usec
> - random_size_alloc_test    loops: 1000000 avg: 5824449  usec
> - fix_align_alloc_test      loops: 1000000 avg: 984735   usec
> All test took worker0=67952362802 cycles
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 40 ++++++++++++++++++++++++++++------------
>  1 file changed, 28 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 9e30f0b39203..0fc38c36e0df 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1825,9 +1825,14 @@ static void free_vmap_area_noflush(struct vmap_area *va)
>  	unsigned long va_start = va->va_start;
>  	unsigned long nr_lazy;
>  
> -	spin_lock(&vmap_area_lock);
> -	unlink_va(va, &vmap_area_root);
> -	spin_unlock(&vmap_area_lock);
> +	/*
> +	 * A free_vmap_block() is left. It is NOT a main free path.
> +	 */
> +	if (!list_empty(&va->list)) {
> +		spin_lock(&vmap_area_lock);
> +		unlink_va(va, &vmap_area_root);
> +		spin_unlock(&vmap_area_lock);
> +	}
>  
>  	nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
>  				PAGE_SHIFT, &vmap_lazy_nr);
> @@ -1871,6 +1876,19 @@ struct vmap_area *find_vmap_area(unsigned long addr)
>  	return va;
>  }
>  
> +static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
> +{
> +	struct vmap_area *va;
> +
> +	spin_lock(&vmap_area_lock);
> +	va = __find_vmap_area(addr, &vmap_area_root);
> +	if (va)
> +		unlink_va(va, &vmap_area_root);
> +	spin_unlock(&vmap_area_lock);
> +
> +	return va;
> +}
> +
>  /*** Per cpu kva allocator ***/
>  
>  /*
> @@ -2236,7 +2254,7 @@ void vm_unmap_ram(const void *mem, unsigned int count)
>  		return;
>  	}
>  
> -	va = find_vmap_area(addr);
> +	va = find_unlink_vmap_area(addr);
>  	BUG_ON(!va);
>  	debug_check_no_locks_freed((void *)va->va_start,
>  				    (va->va_end - va->va_start));
> @@ -2607,21 +2625,16 @@ struct vm_struct *remove_vm_area(const void *addr)
>  
>  	might_sleep();
>  
> -	spin_lock(&vmap_area_lock);
> -	va = __find_vmap_area((unsigned long)addr, &vmap_area_root);
> -	if (va && va->vm) {
> +	va = find_unlink_vmap_area((unsigned long) addr);
> +	if (va) {
>  		struct vm_struct *vm = va->vm;
>  
> -		va->vm = NULL;
> -		spin_unlock(&vmap_area_lock);
> -
>  		kasan_free_module_shadow(vm);
>  		free_unmap_vmap_area(va);
>  
>  		return vm;
>  	}
>  
> -	spin_unlock(&vmap_area_lock);
>  	return NULL;
>  }
>  
> @@ -2690,6 +2703,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
>  static void __vunmap(const void *addr, int deallocate_pages)
>  {
>  	struct vm_struct *area;
> +	struct vmap_area *va;
>  
>  	if (!addr)
>  		return;
> @@ -2698,7 +2712,9 @@ static void __vunmap(const void *addr, int deallocate_pages)
>  			addr))
>  		return;
>  
> -	area = find_vm_area(addr);
> +	va = find_unlink_vmap_area((unsigned long)addr);
> +	area = va->vm;
> +
>  	if (unlikely(!area)) {
>  		WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
>  				addr);
> -- 
> 2.30.2
> 
Will send a v2.

--
Uladzislau Rezki