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[2003:cb:c705:d100:871b:ec55:67d:5247]) by smtp.gmail.com with ESMTPSA id e19-20020a05600c219300b003fbdbd0a7desm17194996wme.27.2023.08.01.11.14.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Aug 2023 11:14:54 -0700 (PDT) Message-ID: <70442e7f-a401-1b4a-3060-ee1d9ac45290@redhat.com> Date: Tue, 1 Aug 2023 20:14:53 +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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , 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> <0af1bc20-8ba2-c6b6-64e6-c1f58d521504@redhat.com> <525a3f14-74fa-4c22-9fca-9dab4de8a0c3@lucifer.local> From: David Hildenbrand Organization: Red Hat In-Reply-To: <525a3f14-74fa-4c22-9fca-9dab4de8a0c3@lucifer.local> 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: 48B302004B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: e3qqsyimeq7gz5unyuzpsy45e1aompec X-HE-Tag: 1690913700-480539 X-HE-Meta: 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 IB5+E9I8 G8b85iudlDX186pKX5Nb+C2F6eOC6P0kDaLCo/l0ycjbXAKSOYUloOeLheHFTi2gPf1bnV1N/XrAJxYvMT/xfIe4abt4LSseIvgS5HHZHXQDi1kan1YJT4JUxJcC1Ae7qWJO2CWl2uTS91TFmSrAmv0Z+IdlQVkB2HkoWCE6UkgXEkshOXxgbfum2yfRaJL2GS5MP7UfSI5z0HVoe5SmlDj0fhhUIPe/7hge+RTKnymBVaO0yjHHWdtBV2vgahnPh0yZtWxoRqS7Id+byap9xBb2kzxPZ/ImiHUuVX9EHTFV47fmjhNQRaSaDRNhmnejbQDLxfffdFe/CkdvEAEtBNDIQStaUrRybUAlmnZ0HwXhyKeD3dKKmm2wDjLVeoxEVxGTOqq/+z9ZKVda/Ey2ugb/GxpvfPb0fizDpcDeDyHNHebXFnPlRzFo+NeNSbhcLwAMzwBrRql9JP/NyFWrv73ntANQhOSCC2cz/ 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: >>> Hm good point, actually, now we're using the bounce buffer we don't need to >>> avoid usermode hardening any more. >>> >>> However since we've established a bounce buffer ourselves its still >>> appropriate to use _copy_to_iter() as we know the source region is good to >>> copy from. >>> >>> To make life easy I'll just respin with an updated comment :) >> >> I'm not too picky this time, no need to resend if everybody else is fine :P >> > > Haha you know the classic Lorenzo respin spiral and want to avoid it I see ;) Don't want to make your apparently stressful week more stressful. Not this time ;) > > The comment is actually inaccurate now, so to avoid noise + make life easy > (maybe) for Andrew here's a fix patch that just corrects the comment:- > > ----8<---- > > From d2b8fb271f21b79048e5630699133f77a93d0481 Mon Sep 17 00:00:00 2001 > From: Lorenzo Stoakes > Date: Tue, 1 Aug 2023 17:36:08 +0100 > Subject: [PATCH] fs/proc/kcore: correct comment > > Correct comment to be strictly correct about reasoning. > > Signed-off-by: Lorenzo Stoakes > --- > fs/proc/kcore.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index 3bc689038232..23fc24d16b31 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -568,8 +568,8 @@ static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > goto out; > } > /* > - * We use _copy_to_iter() to bypass usermode hardening > - * which would otherwise prevent this operation. > + * We know the bounce buffer is safe to copy from, so > + * use _copy_to_iter() directly. > */ > } else if (_copy_to_iter(buf, tsz, iter) != tsz) { > ret = -EFAULT; > -- > 2.41.0 > Thanks! Acked-by: David Hildenbrand -- Cheers, David / dhildenb