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Fri, 8 Aug 2025 14:19:09 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id FdIAIl0HlmghMgAAD6G6ig (envelope-from ); Fri, 08 Aug 2025 14:19:09 +0000 Message-ID: <571c0a24-6bdf-47cd-b336-efff34f48010@suse.cz> Date: Fri, 8 Aug 2025 16:19:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.17 2/3] mm/mremap: catch invalid multi VMA moves earlier Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Jann Horn , Pedro Falcato , David Hildenbrand , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2b5aad5681573be85b5b8fac61399af6fb6b68b6.1754218667.git.lorenzo.stoakes@oracle.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <2b5aad5681573be85b5b8fac61399af6fb6b68b6.1754218667.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: 6123114000F X-Stat-Signature: np1huw8nupxo19jxrfnouiji9iakreib X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1754662751-17732 X-HE-Meta: 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 NGgxhEly yi0tE9ly+njf1dRwLr2vaMZzDStPcyBYwLQ6ucl6nr6LUZjxSGpt1SkiKXBJwgUuaUj8db61qnAOHDn2AMlZkDYec/DAWCh4AWy40A9dPPBqNhIzbsliTNWo6xinWdqD34icGKvDnHSS4TgWmWfYC8f6j3NSZM/FlqQDKuCCFdpLar2Z4k4rSiH1pn2SrppvGc+wL56p2705Wfcc/eytPBpANiwGERTeZN1eDcwkruPsnuVEhgl+JYZwaAKTG3I0BPzuFf3tdCtQdRlWbcGGdBBStV38t8LdWNnAn6kyDCMYlDea/CE0gbRvbIA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/3/25 13:11, Lorenzo Stoakes wrote: > In remap_move() we must account for both a single VMA case, where we are > permitted to move a single VMA regardless of multi-VMA move eligiblity, and > multiple VMAs which, of course, must be eligible for such an operation. > > We determine this via vma_multi_allowed(). > > Currently, if the first VMA is not eligible, but others are, we will move > the first then return an error. This is not ideal, as we are performing an > operation which we don't need to do which has an impact on the memory > mapping. > > We can very easily determine if this is a multi VMA move prior to the move > of the first VMA, by checking vma->vm_end vs. the specified end address. > > Therefore this patch does so, and as a result eliminates unnecessary logic > around tracking whether the first VMA was permitted or not. > > This is most useful for cases where a user attempts to erroneously move > mutliple VMAs which are not eligible for non-transient reasons - for > instance, UFFD-armed VMAs, or file-backed VMAs backed by a file system or > driver which specifies a custom f_op->get_unmapped_area. > > In the less likely instance of a failure due to transient issues such as > out of memory or mapping limits being hit, the issue is already likely > fatal and so the fact the operation may be partially complete is > acceptable. > > Signed-off-by: Lorenzo Stoakes > --- > mm/mremap.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index 46f9f3160dff..f61a9ea0b244 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -1816,10 +1816,11 @@ static unsigned long remap_move(struct vma_remap_struct *vrm) > unsigned long start = vrm->addr; > unsigned long end = vrm->addr + vrm->old_len; > unsigned long new_addr = vrm->new_addr; > - bool allowed = true, seen_vma = false; > unsigned long target_addr = new_addr; > unsigned long res = -EFAULT; > unsigned long last_end; > + bool seen_vma = false; > + > VMA_ITERATOR(vmi, current->mm, start); > > /* > @@ -1833,9 +1834,6 @@ static unsigned long remap_move(struct vma_remap_struct *vrm) > unsigned long len = min(end, vma->vm_end) - addr; > unsigned long offset, res_vma; > > - if (!allowed) > - return -EFAULT; > - > /* No gap permitted at the start of the range. */ > if (!seen_vma && start < vma->vm_start) > return -EFAULT; > @@ -1863,9 +1861,14 @@ static unsigned long remap_move(struct vma_remap_struct *vrm) > vrm->new_addr = target_addr + offset; > vrm->old_len = vrm->new_len = len; > > - allowed = vma_multi_allowed(vma); > - if (seen_vma && !allowed) > - return -EFAULT; > + if (!vma_multi_allowed(vma)) { > + /* This is not the first VMA, abort immediately. */ > + if (seen_vma) > + return -EFAULT; > + /* This is the first, but there are more, abort. */ > + if (vma->vm_end < end) > + return -EFAULT; Hm there can just also be a gap, and we permit gaps at the end (unlike at the start), right? So we might be denying a multi vma mremap for !vma_multi_allowed() reasons even if it's a single vma and a gap. AFAICS this is not regressing the behavior prior to d23cb648e365 ("mm/mremap: permit mremap() move of multiple VMAs") as such mremap() would be denied anyway by the "/* We can't remap across vm area boundaries */" check in check_prep_vma(). So the question is just if we want this odd corner case to behave like this, and if yes then be more explicit about it perhaps. > + } > > res_vma = check_prep_vma(vrm); > if (!res_vma) > @@ -1874,7 +1877,8 @@ static unsigned long remap_move(struct vma_remap_struct *vrm) > return res_vma; > > if (!seen_vma) { > - VM_WARN_ON_ONCE(allowed && res_vma != new_addr); > + VM_WARN_ON_ONCE(vma_multi_allowed(vma) && > + res_vma != new_addr); > res = res_vma; > } >