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[2003:cb:c705:d100:871b:ec55:67d:5247]) by smtp.gmail.com with ESMTPSA id f17-20020adffcd1000000b00313f61889ecsm15587910wrs.66.2023.08.01.02.05.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Aug 2023 02:05:41 -0700 (PDT) Message-ID: <0af1bc20-8ba2-c6b6-64e6-c1f58d521504@redhat.com> Date: Tue, 1 Aug 2023 11:05:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] fs/proc/kcore: reinstate bounce buffer for KCORE_TEXT regions To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Baoquan He , Uladzislau Rezki , linux-fsdevel@vger.kernel.org, Jiri Olsa , Will Deacon , Mike Galbraith , Mark Rutland , wangkefeng.wang@huawei.com, catalin.marinas@arm.com, ardb@kernel.org, Linux regression tracking , regressions@lists.linux.dev, Matthew Wilcox , Liu Shixin , Jens Axboe , Alexander Viro , stable@vger.kernel.org References: <20230731215021.70911-1-lstoakes@gmail.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230731215021.70911-1-lstoakes@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B477380017 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 77fxmyzsok16awkengmh8hxu5io8wsrd X-HE-Tag: 1690880745-401839 X-HE-Meta: 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 /4aCwPlj 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 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: On 31.07.23 23:50, Lorenzo Stoakes wrote: > Some architectures do not populate the entire range categorised by > KCORE_TEXT, so we must ensure that the kernel address we read from is > valid. > > Unfortunately there is no solution currently available to do so with a > purely iterator solution so reinstate the bounce buffer in this instance so > we can use copy_from_kernel_nofault() in order to avoid page faults when > regions are unmapped. > > This change partly reverts commit 2e1c0170771e ("fs/proc/kcore: avoid > bounce buffer for ktext data"), reinstating the bounce buffer, but adapts > the code to continue to use an iterator. > > Fixes: 2e1c0170771e ("fs/proc/kcore: avoid bounce buffer for ktext data") > Reported-by: Jiri Olsa > Closes: https://lore.kernel.org/all/ZHc2fm+9daF6cgCE@krava > Cc: stable@vger.kernel.org > Signed-off-by: Lorenzo Stoakes > --- > fs/proc/kcore.c | 26 +++++++++++++++++++++++++- > 1 file changed, 25 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index 9cb32e1a78a0..3bc689038232 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -309,6 +309,8 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, > > static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > { > + struct file *file = iocb->ki_filp; > + char *buf = file->private_data; > loff_t *fpos = &iocb->ki_pos; > size_t phdrs_offset, notes_offset, data_offset; > size_t page_offline_frozen = 1; > @@ -554,11 +556,22 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > fallthrough; > case KCORE_VMEMMAP: > case KCORE_TEXT: > + /* > + * Sadly we must use a bounce buffer here to be able to > + * make use of copy_from_kernel_nofault(), as these > + * memory regions might not always be mapped on all > + * architectures. > + */ > + if (copy_from_kernel_nofault(buf, (void *)start, tsz)) { > + if (iov_iter_zero(tsz, iter) != tsz) { > + ret = -EFAULT; > + goto out; > + } > /* > * We use _copy_to_iter() to bypass usermode hardening > * which would otherwise prevent this operation. > */ Having a comment at this indentation level looks for the else case looks kind of weird. (does that comment still apply?) -- Cheers, David / dhildenb