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Subject: Re: [kernel-hardening] [PATCH 09/38] usercopy: Mark kmalloc caches as
 usercopy caches
To:     Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>
Cc:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christopher Lameter <cl@linux.com>,
        Julian Wiedmann <jwi@linux.ibm.com>,
        Ursula Braun <ubraun@linux.ibm.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        kernel list <linux-kernel@vger.kernel.org>,
        David Windsor <dave@nullcore.net>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, linux-xfs@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Christoffer Dall <christoffer.dall@linaro.org>,
        Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jan Kara <jack@suse.cz>,
        Luis de Bethencourt <luisbg@kernel.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Rik van Riel <riel@redhat.com>,
        Matthew Garrett <mjg59@google.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Michal Kubecek <mkubecek@suse.cz>
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From:   Jiri Slaby <jslaby@suse.cz>
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Message-ID: <548e6212-7b3c-5925-19f2-699af451fd16@suse.cz>
Date:   Mon, 20 Apr 2020 09:53:20 +0200
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On 07. 04. 20, 10:00, Vlastimil Babka wrote:
> From d5190e4e871689a530da3c3fd327be45a88f006a Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Tue, 7 Apr 2020 09:58:00 +0200
> Subject: [PATCH] usercopy: Mark dma-kmalloc caches as usercopy caches
> 
> We have seen a "usercopy: Kernel memory overwrite attempt detected to SLUB
> object 'dma-kmalloc-1 k' (offset 0, size 11)!" error on s390x, as IUCV uses
> kmalloc() with __GFP_DMA because of memory address restrictions.
> The issue has been discussed [2] and it has been noted that if all the kmalloc
> caches are marked as usercopy, there's little reason not to mark dma-kmalloc
> caches too. The 'dma' part merely means that __GFP_DMA is used to restrict
> memory address range.
> 
> As Jann Horn put it [3]:
> 
> "I think dma-kmalloc slabs should be handled the same way as normal
> kmalloc slabs. When a dma-kmalloc allocation is freshly created, it is
> just normal kernel memory - even if it might later be used for DMA -,
> and it should be perfectly fine to copy_from_user() into such
> allocations at that point, and to copy_to_user() out of them at the
> end. If you look at the places where such allocations are created, you
> can see things like kmemdup(), memcpy() and so on - all normal
> operations that shouldn't conceptually be different from usercopy in
> any relevant way."
> 
> Thus this patch marks the dma-kmalloc-* caches as usercopy.
> 
> [1] https://bugzilla.suse.com/show_bug.cgi?id=1156053
> [2] https://lore.kernel.org/kernel-hardening/bfca96db-bbd0-d958-7732-76e36c667c68@suse.cz/
> [3] https://lore.kernel.org/kernel-hardening/CAG48ez1a4waGk9kB0WLaSbs4muSoK0AYAVk8=XYaKj4_+6e6Hg@mail.gmail.com/
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Friendly ping.

Acked-by: Jiri Slaby <jslaby@suse.cz>

> ---
>  mm/slab_common.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 5282f881d2f5..ae9486160594 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1303,7 +1303,8 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>  			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
>  				kmalloc_info[i].name[KMALLOC_DMA],
>  				kmalloc_info[i].size,
> -				SLAB_CACHE_DMA | flags, 0, 0);
> +				SLAB_CACHE_DMA | flags, 0,
> +				kmalloc_info[i].size);
>  		}
>  	}
>  #endif
> 

thanks,
-- 
js
suse labs