linux-kernel - Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

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Message-ID: <d452d228-9d62-1511-5d87-dc9bd84d0cda@leemhuis.info>
Date:   Mon, 24 Jul 2023 11:38:17 +0200
From:   "Linux regression tracking (Thorsten Leemhuis)" 
        <regressions@...mhuis.info>
To:     Jiri Olsa <olsajiri@...il.com>,
        Lorenzo Stoakes <lstoakes@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Uladzislau Rezki <urezki@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux kernel regressions list <regressions@...ts.linux.dev>
Subject: Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

[CCing the regression list, as it should be in the loop for regressions:
https://docs.kernel.org/admin-guide/reporting-regressions.html]

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
See link in footer if these mails annoy you.]

On 31.05.23 13:58, Jiri Olsa wrote:
> On Thu, Mar 23, 2023 at 10:15:16AM +0000, Lorenzo Stoakes wrote:
>> Commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
>> introduced the use of a bounce buffer to retrieve kernel text data for
>> /proc/kcore in order to avoid failures arising from hardened user copies
>> enabled by CONFIG_HARDENED_USERCOPY in check_kernel_text_object().
>> [...]
>> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
>> Reviewed-by: David Hildenbrand <david@...hat.com>
> 
> sorry for late feedback, but looks like this one breaks reading
> /proc/kcore with objdump for me:
> 
>   # cat /proc/kallsyms | grep ksys_read
>   ffffffff8150ebc0 T ksys_read
>   # objdump -d  --start-address=0xffffffff8150ebc0 --stop-address=0xffffffff8150ebd0 /proc/kcore 
> 
>   /proc/kcore:     file format elf64-x86-64
> 
>   objdump: Reading section load1 failed because: Bad address
> 
> reverting this makes it work again

Thanks for the report. To be sure the issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
tracking bot:

#regzbot ^introduced 2e1c017077
#regzbot title mm / fs/proc/kcore: reading /proc/kcore with objdump broke
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply and tell me -- ideally
while also telling regzbot about it, as explained by the page listed in
the footer of this mail.

Developers: When fixing the issue, remember to add 'Link:' tags pointing
to the report (the parent of this mail). See page linked in footer for
details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
That page also explains what to do if mails like this annoy you.