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Mon, 10 Jun 2024 20:54:26 +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 I8UqLgJoZ2YOLQAAD6G6ig (envelope-from ); Mon, 10 Jun 2024 20:54:26 +0000 Message-ID: <8b844d71-01f1-472b-a63a-4c9cdb26e9ef@suse.cz> Date: Mon, 10 Jun 2024 22:54:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] slab: make check_object() more consistent Content-Language: en-US To: "Christoph Lameter (Ampere)" , Chengming Zhou Cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Feng Tang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com, Kees Cook References: <20240607-b4-slab-debug-v3-0-bb2a326c4ceb@linux.dev> <20240607-b4-slab-debug-v3-1-bb2a326c4ceb@linux.dev> <63da08b7-7aa3-3fad-55e6-9fc3928a49de@gentwo.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: <63da08b7-7aa3-3fad-55e6-9fc3928a49de@gentwo.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: AFDBC1A0005 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: 9ipyntfxet1mspaxmxixdeaq58u5wrc4 X-HE-Tag: 1718052868-298423 X-HE-Meta: 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 g3JMlJTb vogYU7sEFjYxrxR2ne+iy/sfKl03yGLO7dWLLo+sk6FFVj1PvM1BD0Ud0EcNyZlnFqaNiafXlZi/67oDhLN9uIr4USCFTHyOggcIqRS0SwO+YEpwWKubDwma1/bD1vNxrSn6q2ypyVSTDfjJKgu3sNnT3iC+vv2JVS/ShdJKgE1Pav4uCIHpfQ9gSkx8uNygYeVpMbApx0oPH1KGlcVja7x7WmXxrcRJ5UN2NkjwWxzjFZ/ePo00f5jp+GPCSxbUl1c3BfiOjza0zmzNwPJDx3evfs7aEdx/QQX8yib5r5YZN0FszwC9Ony/Yl6zccEUOroHBbjVdrsS/LO2P+3N+fDkX8UtheVeC2gbJTSE6GAwyfkQjJHRkdKCokZEdJkZIRAKK 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 6/10/24 7:07 PM, Christoph Lameter (Ampere) wrote: > On Fri, 7 Jun 2024, Chengming Zhou wrote: > >> There are two inconsistencies in check_object(), which are alignment >> padding checking and object padding checking. We only print the error >> messages but don't return 0 to tell callers that something is wrong >> and needs to be handled. Please see alloc_debug_processing() and >> free_debug_processing() for details. > > If the error is in the padding and the redzones are ok then its likely > that the objects are ok. So we can actually continue with this slab page > instead of isolating it. > > We isolate it in the case that the redzones have been violated because > that suggests someone overwrote the end of the object f.e. In that case > objects may be corrupted. Its best to isolate the slab and hope for the > best. > > If it was just the padding then the assumption is that this may be a > scribble. So clean it up and continue. Hm is it really worth such nuance? We enabled debugging and actually hit a bug. I think it's best to keep things as much as they were and not try to allow further changes. This e.g. allows more detailed analysis if somebody later notices the bug report and decides to get a kdump crash dump (or use drgn on live system). Maybe we should even stop doing the restore_bytes() stuff, and prevent any further frees in the slab page to happen if possible without affecting fast paths (now we mark everything as used but don't prevent further frees of objects that were actually allocated before). Even if some security people enable parts of slub debugging for security people it is my impression they would rather panic/reboot or have memory leaked than trying to salvage the slab page? (CC Kees)