linux-kernel - Re: [PATCH] fs/proc/kcore: reinstate bounce buffer for KCORE

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Message-ID: <70442e7f-a401-1b4a-3060-ee1d9ac45290@redhat.com>
Date:   Tue, 1 Aug 2023 20:14:53 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Uladzislau Rezki <urezki@...il.com>,
        linux-fsdevel@...r.kernel.org, Jiri Olsa <olsajiri@...il.com>,
        Will Deacon <will@...nel.org>, Mike Galbraith <efault@....de>,
        Mark Rutland <mark.rutland@....com>,
        wangkefeng.wang@...wei.com, catalin.marinas@....com,
        ardb@...nel.org,
        Linux regression tracking <regressions@...mhuis.info>,
        regressions@...ts.linux.dev, Matthew Wilcox <willy@...radead.org>,
        Liu Shixin <liushixin2@...wei.com>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        stable@...r.kernel.org
Subject: Re: [PATCH] fs/proc/kcore: reinstate bounce buffer for KCORE_TEXT
 regions

>>> 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 <lstoakes@...il.com>
> 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 <lstoakes@...il.com>
> ---
>   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 <david@...hat.com>

-- 
Cheers,

David / dhildenb