From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Michael Ellerman <mpe@ellerman.id.au>, Will Deacon <will@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
danielwa@cisco.com, robh@kernel.org,
daniel@gimpelevich.san-francisco.ca.us,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arch@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v2 1/7] cmdline: Add generic function to build command line.
Date: Fri, 5 Mar 2021 13:49:03 +0100 [thread overview]
Message-ID: <11d7af27-28cb-0eed-0f33-6669cbf7f1bb@csgroup.eu> (raw)
In-Reply-To: <87sg59rewl.fsf@mpe.ellerman.id.au>
Le 05/03/2021 à 12:58, Michael Ellerman a écrit :
> Will Deacon <will@kernel.org> writes:
>> On Wed, Mar 03, 2021 at 06:57:09PM +0100, Christophe Leroy wrote:
>>> Le 03/03/2021 à 18:46, Will Deacon a écrit :
>>>> On Wed, Mar 03, 2021 at 06:38:16PM +0100, Christophe Leroy wrote:
>>>>> Le 03/03/2021 à 18:28, Will Deacon a écrit :
>>>>>> On Tue, Mar 02, 2021 at 05:25:17PM +0000, Christophe Leroy wrote:
>>>>>>> This code provides architectures with a way to build command line
>>>>>>> based on what is built in the kernel and what is handed over by the
>>>>>>> bootloader, based on selected compile-time options.
>>>>>>>
>>>>>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>>>>>>> ---
>>>>>>> include/linux/cmdline.h | 62 +++++++++++++++++++++++++++++++++++++++++
>>>>>>> 1 file changed, 62 insertions(+)
>>>>>>> create mode 100644 include/linux/cmdline.h
>>>>>>>
>>>>>>> diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..ae3610bb0ee2
>>>>>>> --- /dev/null
>>>>>>> +++ b/include/linux/cmdline.h
>>>>>>> @@ -0,0 +1,62 @@
>>>>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>>>>> +#ifndef _LINUX_CMDLINE_H
>>>>>>> +#define _LINUX_CMDLINE_H
>>>>>>> +
>>>>>>> +static __always_inline size_t cmdline_strlen(const char *s)
>>>>>>> +{
>>>>>>> + const char *sc;
>>>>>>> +
>>>>>>> + for (sc = s; *sc != '\0'; ++sc)
>>>>>>> + ; /* nothing */
>>>>>>> + return sc - s;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static __always_inline size_t cmdline_strlcat(char *dest, const char *src, size_t count)
>>>>>>> +{
>>>>>>> + size_t dsize = cmdline_strlen(dest);
>>>>>>> + size_t len = cmdline_strlen(src);
>>>>>>> + size_t res = dsize + len;
>>>>>>> +
>>>>>>> + /* This would be a bug */
>>>>>>> + if (dsize >= count)
>>>>>>> + return count;
>>>>>>> +
>>>>>>> + dest += dsize;
>>>>>>> + count -= dsize;
>>>>>>> + if (len >= count)
>>>>>>> + len = count - 1;
>>>>>>> + memcpy(dest, src, len);
>>>>>>> + dest[len] = 0;
>>>>>>> + return res;
>>>>>>> +}
>>>>>>
>>>>>> Why are these needed instead of using strlen and strlcat directly?
>>>>>
>>>>> Because on powerpc (at least), it will be used in prom_init, it is very
>>>>> early in the boot and KASAN shadow memory is not set up yet so calling
>>>>> generic string functions would crash the board.
>>>>
>>>> Hmm. We deliberately setup a _really_ early shadow on arm64 for this, can
>>>> you not do something similar? Failing that, I think it would be better to
>>>> offer the option for an arch to implement cmdline_*, but have then point to
>>>> the normal library routines by default.
>>>
>>> I don't think it is possible to setup an earlier early shadow.
>>>
>>> At the point we are in prom_init, the code is not yet relocated at the
>>> address it was linked for, and it is running with the MMU set by the
>>> bootloader, I can't imagine being able to setup MMU entries for the early
>>> shadow KASAN yet without breaking everything.
>>
>> That's very similar to us; we're not relocated, although we are at least
>> in control of the MMU (which is using a temporary set of page-tables).
>
> prom_init runs as an OF client, with the MMU off (except on some Apple
> machines), and we don't own the MMU. So there's really nothing we can do :)
>
> Though now that I look at it, I don't think we should be doing this
> level of commandline handling in prom_init. It should just grab the
> value from firmware and pass it to the kernel proper, and then all the
> prepend/append/force etc. logic should happen there.
But then, how do you handle the command line parameters that are needed by prom_init ?
For instance, prom_init_mem() use 'prom_memory_limit', which comes from the "mem=" option in the
command line.
Christophe
next prev parent reply other threads:[~2021-03-05 12:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 17:25 [PATCH v2 0/7] Improve boot command line handling Christophe Leroy
2021-03-02 17:25 ` [PATCH v2 1/7] cmdline: Add generic function to build command line Christophe Leroy
2021-03-03 17:28 ` Will Deacon
2021-03-03 17:38 ` Christophe Leroy
2021-03-03 17:46 ` Will Deacon
2021-03-03 17:57 ` Christophe Leroy
2021-03-03 18:16 ` Will Deacon
2021-03-05 11:58 ` Michael Ellerman
2021-03-05 12:49 ` Christophe Leroy [this message]
2021-03-05 18:35 ` Segher Boessenkool
2021-03-05 18:33 ` Segher Boessenkool
2021-03-03 17:39 ` Will Deacon
2021-03-02 17:25 ` [PATCH v2 2/7] drivers: of: use cmdline building function Christophe Leroy
2021-03-02 17:25 ` [PATCH v2 3/7] powerpc: convert to generic builtin command line Christophe Leroy
2021-03-02 17:25 ` [PATCH v2 4/7] cmdline: Add capability to prepend the " Christophe Leroy
2021-03-03 18:19 ` Will Deacon
2021-03-02 17:25 ` [PATCH v2 5/7] powerpc: add capability to prepend default " Christophe Leroy
2021-03-02 17:25 ` [PATCH v2 6/7] cmdline: Gives architectures opportunity to use generically defined boot cmdline manipulation Christophe Leroy
2021-03-02 19:30 ` kernel test robot
2021-03-03 17:57 ` Will Deacon
2021-03-25 11:18 ` Christophe Leroy
2021-03-25 19:32 ` Will Deacon
2021-03-26 6:18 ` Christophe Leroy
2021-03-26 6:44 ` Christophe Leroy
2021-03-02 17:25 ` [PATCH v2 7/7] powerpc: use generic CMDLINE manipulations Christophe Leroy
2021-03-02 17:35 ` [PATCH v2 0/7] Improve boot command line handling Daniel Walker
2021-03-02 17:39 ` Christophe Leroy
2021-03-03 2:01 ` Rob Herring
2021-03-03 17:39 ` Daniel Walker
2021-03-03 18:07 ` Christophe Leroy
2021-03-03 18:53 ` Daniel Walker
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