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Tue, 30 Jul 2024 21:06:56 +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 BGd8DvBVqWaRVwAAD6G6ig (envelope-from ); Tue, 30 Jul 2024 21:06:56 +0000 Message-ID: <9369adda-9cb9-4447-92fa-b7a70bd81fb6@suse.cz> Date: Tue, 30 Jul 2024 23:06:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: krealloc: consider spare memory for __GFP_ZERO Content-Language: en-US To: Andrew Morton , Danilo Krummrich Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240730194214.31483-1-dakr@kernel.org> <20240730133111.d180e1a6fc63b2883fe99821@linux-foundation.org> 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: <20240730133111.d180e1a6fc63b2883fe99821@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2122B18000C X-Stat-Signature: 33sqc1f5c5qhshfyiyzywtowjmeu5fh8 X-HE-Tag: 1722373617-824788 X-HE-Meta: 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 WYN4nt45 SBtBgzXosj5ZoRylbXIyFX15VUwKf2egOIHxCi4q1A923aTwg7LANEYlwY3EiyiqVBX7ARqcPlzFqsomfTTONSLqJjq5bm95EarQi7FJ/0QoWNUWCsotRB9kQW8WJ1mjQ7FMjfTbBCZneRMlqxzjjvH8UbBkltZgedBMmmrdl90nAz39Ys8FyAGckE6bs+u9yIibO0/bbrsv5TPp4pIkQFBBZOkAqX6kQpmPEHA2xWRNLyllODgXvixYqvFQgsylYxV+WWQmG13b7ldtIOOOHjcBNq4JFTVEdtOchoTislcdJMVAXdCWbaGOAAmgKdpi2qNelQKeulandK0UXhAY8ZqD9Lu2757HixvhWhfh7kK6t5bDK4g1kSpy5B67pdU28rBd+zz2aPynL5eua3gw4Z692pAa8BCHpPgicz6fqUqMjl/Ku/w3FISrN6A== 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 7/30/24 10:31 PM, Andrew Morton wrote: > On Tue, 30 Jul 2024 21:42:05 +0200 Danilo Krummrich wrote: > >> As long as krealloc() is called with __GFP_ZERO consistently, starting >> with the initial memory allocation, __GFP_ZERO should be fully honored. >> >> However, if for an existing allocation krealloc() is called with a >> decreased size, it is not ensured that the spare portion the allocation >> is zeroed. Thus, if krealloc() is subsequently called with a larger size >> again, __GFP_ZERO can't be fully honored, since we don't know the >> previous size, but only the bucket size. > > Well that's bad. > >> Example: >> >> buf = kzalloc(64, GFP_KERNEL); > > If this was kmalloc() Then already here we have unitialized kernel memory that a buggy user could expose, no? >> memset(buf, 0xff, 64); >> >> buf = krealloc(buf, 48, GFP_KERNEL | __GFP_ZERO); >> >> /* After this call the last 16 bytes are still 0xff. */ >> buf = krealloc(buf, 64, GFP_KERNEL | __GFP_ZERO); > > then this would expose uninitialized kernel memory to kernel code, with > a risk that the kernel code will expose that to userspace, yes? > > This does seem rather a trap, and I wonder whether krealloc() should > just zero out any such data by default. So unless I'm missing how this differs from plain kmalloc(), relying on want_init_on_alloc() seems the right way how to opt-in harden against this potential exposure. >> Fix this, by explicitly setting spare memory to zero, when shrinking an >> allocation with __GFP_ZERO flag set or init_on_alloc enabled. >> >> --- a/mm/slab_common.c >> +++ b/mm/slab_common.c >> @@ -1273,6 +1273,13 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags) >> >> /* If the object still fits, repoison it precisely. */ >> if (ks >= new_size) { >> + /* Zero out spare memory. */ >> + if (want_init_on_alloc(flags)) { >> + kasan_disable_current(); >> + memset((void *)p + new_size, 0, ks - new_size); > > Casting away the constness of `*p'. This is just misleading everyone, > really. It would be better to make argument `p' have type "void *". > >> + kasan_enable_current(); >> + } >> + >> p = kasan_krealloc((void *)p, new_size, flags); >