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Message-Id: <aecba9ae-887d-39c5-c3b7-8236fbcaa898@de.ibm.com>
Date: Tue, 7 Apr 2020 13:05:46 +0200
From: Christian Borntraeger <borntraeger@...ibm.com>
To: Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
Kees Cook <keescook@...omium.org>
Cc: Christoph Hellwig <hch@...radead.org>, Christopher Lameter
<cl@...ux.com>,
Jiri Slaby <jslaby@...e.cz>, Julian Wiedmann <jwi@...ux.ibm.com>,
Ursula Braun <ubraun@...ux.ibm.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
kernel list <linux-kernel@...r.kernel.org>,
David Windsor
<dave@...lcore.net>, Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>, linux-xfs@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
Dave Kleikamp <dave.kleikamp@...cle.com>, Jan Kara <jack@...e.cz>,
Luis de Bethencourt <luisbg@...nel.org>,
Marc Zyngier
<marc.zyngier@....com>, Rik van Riel <riel@...hat.com>,
Matthew Garrett <mjg59@...gle.com>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH 09/38] usercopy: Mark kmalloc caches as
usercopy caches
On 07.04.20 10:00, Vlastimil Babka wrote:
> On 1/31/20 1:03 PM, Jann Horn wrote:
>
>> 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.
>
> So, let's do that?
>
> ----8<----
> From d5190e4e871689a530da3c3fd327be45a88f006a Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@...e.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@...e.cz>
Acked-by: Christian Borntraeger <borntraeger@...ibm.com>
> ---
> 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
>
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