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V" , Donet Tom , Pavithra Prakash , LKML , "Ritesh Harjani (IBM)" , Disha Goel Subject: Re: [PATCH v3 01/12] powerpc: mm/fault: Fix kfence page fault reporting In-Reply-To: References: Date: Tue, 22 Oct 2024 13:42:29 +1100 Message-ID: <87plnsoo2y.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Queue-Id: 2FCD51A000B X-Rspamd-Server: rspam01 X-Stat-Signature: ie95dmagnue333sf33a31dsz7an9fpsg X-HE-Tag: 1729564935-684379 X-HE-Meta: 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 7WpqpEUD Rg5vkwxz4k0mqRMfxP5kYapehovuH7jeimwAIW+FuMFhoEo1AUbWxBFaYrQMEQ99HTxrl80ZtHfjg5kw8BnPWzIUc8+8YHAQp09X1VKB8Q6TZQ8v+KD9sY9t5zB/T3cyH/Aiiqb+C9qGSf1idJwZB1pchg3cUMmM1YUvR5Lb3/6chvyCz2bL6/JWWT5MBMBMzIxs4az2xOdNHwfYzZQHup34g47f7zuTG8VPYII84mf2mzw3yBEyLX+UtLFo06nRWTuRTc0tK0zSLvtm/qe2b6ZpDYw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Ritesh, "Ritesh Harjani (IBM)" writes: > copy_from_kernel_nofault() can be called when doing read of /proc/kcore. > /proc/kcore can have some unmapped kfence objects which when read via > copy_from_kernel_nofault() can cause page faults. Since *_nofault() > functions define their own fixup table for handling fault, use that > instead of asking kfence to handle such faults. > > Hence we search the exception tables for the nip which generated the > fault. If there is an entry then we let the fixup table handler handle the > page fault by returning an error from within ___do_page_fault(). > > This can be easily triggered if someone tries to do dd from /proc/kcore. > dd if=/proc/kcore of=/dev/null bs=1M > > > =============================== > BUG: KFENCE: invalid read in copy_from_kernel_nofault+0xb0/0x1c8 > Invalid read at 0x000000004f749d2e: > copy_from_kernel_nofault+0xb0/0x1c8 > 0xc0000000057f7950 > read_kcore_iter+0x41c/0x9ac > proc_reg_read_iter+0xe4/0x16c > vfs_read+0x2e4/0x3b0 > ksys_read+0x88/0x154 > system_call_exception+0x124/0x340 > system_call_common+0x160/0x2c4 I haven't been able to reproduce this. Can you give some more details on the exact machine/kernel-config/setup where you saw this? cheers