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Tue, 12 Nov 2024 10:40:01 +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 3PMHAIEwM2fJNAAAD6G6ig (envelope-from ); Tue, 12 Nov 2024 10:40:00 +0000 Message-ID: <751739c3-2d33-4759-b9cf-a02d35391cbb@suse.cz> Date: Tue, 12 Nov 2024 11:40:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/mremap: Fix address wraparound in move_page_tables() Content-Language: en-US To: Jann Horn , Andrew Morton Cc: "Joel Fernandes (Google)" , Lorenzo Stoakes , "Liam R. Howlett" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20241111-fix-mremap-32bit-wrap-v1-1-61d6be73b722@google.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+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20241111-fix-mremap-32bit-wrap-v1-1-61d6be73b722@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E573D40009 X-Stat-Signature: 914ygrd4htag9fo1swatxg1cyardwfnr X-HE-Tag: 1731407970-265362 X-HE-Meta: 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 mA6zJ6WJ z1nB9043094KMWlYoiOnKbpxLsJRKojUwkNxGmKKZJWJS6ZwVaILbpz5SUrRQVypogpVGh4FfY7miABBuFhOp0XSN9I8mL3tBSpbmjWQQudgs7iwWggJ1zGjlHFWMnW7gXidoG34mbDFMC3nC0AgjGVwrc5mPIgWGdP17CG/Ip0J+w9ldxWwLcChKzDJnyu4lyKXlidr6FLd/1FeQH3mPl56aujUa/553+s/8efBPVUUrTcy6UC8aBd+MIdmPVcT7jQpXeMqoKbojOvUUl7F4Atm9p7nm5Dt3TGlDQGgfXRetEWDnysdmsgcruGyN3TW6MdOgXaAEjJspVe54QWXQd8FdMLBuxyjuLC7QU+xlcXF8weaoKRSP0FL6be0BSsBfOdHb 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 11/11/24 20:34, Jann Horn wrote: > On 32-bit platforms, it is possible for the expression > `len + old_addr < old_end` to be false-positive if `len + old_addr` wraps > around. `old_addr` is the cursor in the old range up to which page table > entries have been moved; so if the operation succeeded, `old_addr` is the > *end* of the old region, and adding `len` to it can wrap. > > The overflow causes mremap() to mistakenly believe that PTEs have been > copied; the consequence is that mremap() bails out, but doesn't move the > PTEs back before the new VMA is unmapped, causing anonymous pages in the > region to be lost. So basically if userspace tries to mremap() a > private-anon region and hits this bug, mremap() will return an error and > the private-anon region's contents appear to have been zeroed. > > The idea of this check is that `old_end - len` is the original start > address, and writing the check that way also makes it easier to read; so > fix the check by rearranging the comparison accordingly. > > (An alternate fix would be to refactor this function by introducing an > "orig_old_start" variable or such.) > > Cc: stable@vger.kernel.org > Fixes: af8ca1c14906 ("mm/mremap: optimize the start addresses in move_page_tables()") > Signed-off-by: Jann Horn Acked-by: Vlastimil Babka Thanks! > --- > Tested in a VM with a 32-bit X86 kernel; without the patch: > > ``` > user@horn:~/big_mremap$ cat test.c > #define _GNU_SOURCE > #include > #include > #include > #include > > #define ADDR1 ((void*)0x60000000) > #define ADDR2 ((void*)0x10000000) > #define SIZE 0x50000000uL > > int main(void) { > unsigned char *p1 = mmap(ADDR1, SIZE, PROT_READ|PROT_WRITE, > MAP_ANONYMOUS|MAP_PRIVATE|MAP_FIXED_NOREPLACE, -1, 0); > if (p1 == MAP_FAILED) > err(1, "mmap 1"); > unsigned char *p2 = mmap(ADDR2, SIZE, PROT_NONE, > MAP_ANONYMOUS|MAP_PRIVATE|MAP_FIXED_NOREPLACE, -1, 0); > if (p2 == MAP_FAILED) > err(1, "mmap 2"); > *p1 = 0x41; > printf("first char is 0x%02hhx\n", *p1); > unsigned char *p3 = mremap(p1, SIZE, SIZE, > MREMAP_MAYMOVE|MREMAP_FIXED, p2); > if (p3 == MAP_FAILED) { > printf("mremap() failed; first char is 0x%02hhx\n", *p1); > } else { > printf("mremap() succeeded; first char is 0x%02hhx\n", *p3); > } > } > user@horn:~/big_mremap$ gcc -static -o test test.c > user@horn:~/big_mremap$ setarch -R ./test > first char is 0x41 > mremap() failed; first char is 0x00 > ``` > > With the patch: > > ``` > user@horn:~/big_mremap$ setarch -R ./test > first char is 0x41 > mremap() succeeded; first char is 0x41 > ``` > --- > mm/mremap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index dda09e957a5d4c2546934b796e862e5e0213b311..dee98ff2bbd64439200dddac16c4bd054537c2ed 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -648,7 +648,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, > * Prevent negative return values when {old,new}_addr was realigned > * but we broke out of the above loop for the first PMD itself. > */ > - if (len + old_addr < old_end) > + if (old_addr < old_end - len) > return 0; > > return len + old_addr - old_end; /* how much done */ > > --- > base-commit: 2d5404caa8c7bb5c4e0435f94b28834ae5456623 > change-id: 20241111-fix-mremap-32bit-wrap-747105730f20 >