diff mbox series

[v2,1/7] cmdline: Add generic function to build command line.

Message ID d8cf7979ad986de45301b39a757c268d9df19f35.1614705851.git.christophe.leroy@csgroup.eu
State New
Headers show
Series Improve boot command line handling | expand

Commit Message

Christophe Leroy March 2, 2021, 5:25 p.m. UTC 
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

Comments

Will Deacon March 3, 2021, 5:28 p.m. UTC | #1 
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?

> +/*
> + * This function will append a builtin command line to the command
> + * line provided by the bootloader. Kconfig options can be used to alter
> + * the behavior of this builtin command line.
> + * @dest: The destination of the final appended/prepended string.
> + * @src: The starting string or NULL if there isn't one. Must not equal dest.
> + * @length: the length of dest buffer.
> + */
> +static __always_inline void cmdline_build(char *dest, const char *src, size_t length)
> +{
> +	if (length <= 0)
> +		return;
> +
> +	dest[0] = 0;
> +
> +#ifdef CONFIG_CMDLINE
> +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {
> +		cmdline_strlcat(dest, CONFIG_CMDLINE, length);
> +		return;
> +	}
> +#endif

CONFIG_CMDLINE_FORCE implies CONFIG_CMDLINE, and even if it didn't,
CONFIG_CMDLINE is at worst an empty string. Can you drop the #ifdef?

> +	if (dest != src)
> +		cmdline_strlcat(dest, src, length);
> +#ifdef CONFIG_CMDLINE
> +	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)
> +		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);
> +#endif

Likewise, but also I'm not sure why the sizeof() is required.

Will
Christophe Leroy March 3, 2021, 5:38 p.m. UTC | #2 
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.

> 

>> +/*

>> + * This function will append a builtin command line to the command

>> + * line provided by the bootloader. Kconfig options can be used to alter

>> + * the behavior of this builtin command line.

>> + * @dest: The destination of the final appended/prepended string.

>> + * @src: The starting string or NULL if there isn't one. Must not equal dest.

>> + * @length: the length of dest buffer.

>> + */

>> +static __always_inline void cmdline_build(char *dest, const char *src, size_t length)

>> +{

>> +	if (length <= 0)

>> +		return;

>> +

>> +	dest[0] = 0;

>> +

>> +#ifdef CONFIG_CMDLINE

>> +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {

>> +		cmdline_strlcat(dest, CONFIG_CMDLINE, length);

>> +		return;

>> +	}

>> +#endif

> 

> CONFIG_CMDLINE_FORCE implies CONFIG_CMDLINE, and even if it didn't,

> CONFIG_CMDLINE is at worst an empty string. Can you drop the #ifdef?


Ah yes, since cbe46bd4f510 ("powerpc: remove CONFIG_CMDLINE #ifdef mess") it is feasible. I can 
change that now.

> 

>> +	if (dest != src)

>> +		cmdline_strlcat(dest, src, length);

>> +#ifdef CONFIG_CMDLINE

>> +	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)

>> +		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);

>> +#endif

> 

> Likewise, but also I'm not sure why the sizeof() is required.


It is to avoid adding a white space at the end of the command line when CONFIG_CMDLINE is empty. But 
maybe it doesn't matter ?

Christophe
Will Deacon March 3, 2021, 5:39 p.m. UTC | #3 
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


Sorry, spotted a couple of other things...

> +/*

> + * This function will append a builtin command line to the command

> + * line provided by the bootloader. Kconfig options can be used to alter

> + * the behavior of this builtin command line.

> + * @dest: The destination of the final appended/prepended string.

> + * @src: The starting string or NULL if there isn't one. Must not equal dest.

> + * @length: the length of dest buffer.

> + */

> +static __always_inline void cmdline_build(char *dest, const char *src, size_t length)

> +{

> +	if (length <= 0)

> +		return;


length is unsigned

> +

> +	dest[0] = 0;

> +

> +#ifdef CONFIG_CMDLINE

> +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {

> +		cmdline_strlcat(dest, CONFIG_CMDLINE, length);

> +		return;

> +	}

> +#endif

> +	if (dest != src)


The kernel-doc says that @src "Must not equal dest".

Will
Will Deacon March 3, 2021, 5:46 p.m. UTC | #4 
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.

> > > +/*
> > > + * This function will append a builtin command line to the command
> > > + * line provided by the bootloader. Kconfig options can be used to alter
> > > + * the behavior of this builtin command line.
> > > + * @dest: The destination of the final appended/prepended string.
> > > + * @src: The starting string or NULL if there isn't one. Must not equal dest.
> > > + * @length: the length of dest buffer.
> > > + */
> > > +static __always_inline void cmdline_build(char *dest, const char *src, size_t length)
> > > +{
> > > +	if (length <= 0)
> > > +		return;
> > > +
> > > +	dest[0] = 0;
> > > +
> > > +#ifdef CONFIG_CMDLINE
> > > +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {
> > > +		cmdline_strlcat(dest, CONFIG_CMDLINE, length);
> > > +		return;
> > > +	}
> > > +#endif
> > 
> > CONFIG_CMDLINE_FORCE implies CONFIG_CMDLINE, and even if it didn't,
> > CONFIG_CMDLINE is at worst an empty string. Can you drop the #ifdef?
> 
> Ah yes, since cbe46bd4f510 ("powerpc: remove CONFIG_CMDLINE #ifdef mess") it
> is feasible. I can change that now.
> 
> > 
> > > +	if (dest != src)
> > > +		cmdline_strlcat(dest, src, length);
> > > +#ifdef CONFIG_CMDLINE
> > > +	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)
> > > +		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);
> > > +#endif
> > 
> > Likewise, but also I'm not sure why the sizeof() is required.
> 
> It is to avoid adding a white space at the end of the command line when
> CONFIG_CMDLINE is empty. But maybe it doesn't matter ?

If CONFIG_CMDLINE is empty, I don't think you can select
CONFIG_CMDLINE_EXTEND (but even if you could, I don't think it matters).

Will
Christophe Leroy March 3, 2021, 5:57 p.m. UTC | #5 
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.

Is it really worth trying to point to the normal library routines by default ? It is really only a 
few lines of code hence only not many bytes, and anyway they are in __init section so they get 
discarded at the end.

> 

>>>> +/*

>>>> + * This function will append a builtin command line to the command

>>>> + * line provided by the bootloader. Kconfig options can be used to alter

>>>> + * the behavior of this builtin command line.

>>>> + * @dest: The destination of the final appended/prepended string.

>>>> + * @src: The starting string or NULL if there isn't one. Must not equal dest.

>>>> + * @length: the length of dest buffer.

>>>> + */

>>>> +static __always_inline void cmdline_build(char *dest, const char *src, size_t length)

>>>> +{

>>>> +	if (length <= 0)

>>>> +		return;

>>>> +

>>>> +	dest[0] = 0;

>>>> +

>>>> +#ifdef CONFIG_CMDLINE

>>>> +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {

>>>> +		cmdline_strlcat(dest, CONFIG_CMDLINE, length);

>>>> +		return;

>>>> +	}

>>>> +#endif

>>>

>>> CONFIG_CMDLINE_FORCE implies CONFIG_CMDLINE, and even if it didn't,

>>> CONFIG_CMDLINE is at worst an empty string. Can you drop the #ifdef?

>>

>> Ah yes, since cbe46bd4f510 ("powerpc: remove CONFIG_CMDLINE #ifdef mess") it

>> is feasible. I can change that now.

>>

>>>

>>>> +	if (dest != src)

>>>> +		cmdline_strlcat(dest, src, length);

>>>> +#ifdef CONFIG_CMDLINE

>>>> +	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)

>>>> +		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);

>>>> +#endif

>>>

>>> Likewise, but also I'm not sure why the sizeof() is required.

>>

>> It is to avoid adding a white space at the end of the command line when

>> CONFIG_CMDLINE is empty. But maybe it doesn't matter ?

> 

> If CONFIG_CMDLINE is empty, I don't think you can select

> CONFIG_CMDLINE_EXTEND (but even if you could, I don't think it matters).


Ok I'll simplify that when I re-spin.

Christophe
Will Deacon March 3, 2021, 6:16 p.m. UTC | #6 
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).

> Is it really worth trying to point to the normal library routines by default

> ? It is really only a few lines of code hence only not many bytes, and

> anyway they are in __init section so they get discarded at the end.


I would prefer to use the normal routines by default and allow architectures
to override them based on their needs, otherwise we'll end up trying to
maintain a "lowest-common-dominator" set of string routines that can be
safely run in whatever different constraints different architectures have.

Will
Michael Ellerman March 5, 2021, 11:58 a.m. UTC | #7 
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.

cheers
Christophe Leroy March 5, 2021, 12:49 p.m. UTC | #8 
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
Segher Boessenkool March 5, 2021, 6:33 p.m. UTC | #9 
On Fri, Mar 05, 2021 at 10:58:02PM +1100, Michael Ellerman wrote:
> Will Deacon <will@kernel.org> writes:

> > 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 :)


You *could* take over all memory mapping.  This is complex, and I
estimate the change you get this to work correctly on all supported
systems to be between -400% and 0%.

And not very long later Linux jettisons OF completely anyway.

> 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.


That sounds much simpler, yes :-)


Segher
Segher Boessenkool March 5, 2021, 6:35 p.m. UTC | #10 
On Fri, Mar 05, 2021 at 01:49:03PM +0100, Christophe Leroy wrote:
> Le 05/03/2021 à 12:58, Michael Ellerman a écrit :

> >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.


*Reading* it is easy, much easier than modifying it.


Segher
diff mbox series

Patch

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;
+}
+
+/*
+ * This function will append a builtin command line to the command
+ * line provided by the bootloader. Kconfig options can be used to alter
+ * the behavior of this builtin command line.
+ * @dest: The destination of the final appended/prepended string.
+ * @src: The starting string or NULL if there isn't one. Must not equal dest.
+ * @length: the length of dest buffer.
+ */
+static __always_inline void cmdline_build(char *dest, const char *src, size_t length)
+{
+	if (length <= 0)
+		return;
+
+	dest[0] = 0;
+
+#ifdef CONFIG_CMDLINE
+	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {
+		cmdline_strlcat(dest, CONFIG_CMDLINE, length);
+		return;
+	}
+#endif
+	if (dest != src)
+		cmdline_strlcat(dest, src, length);
+#ifdef CONFIG_CMDLINE
+	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)
+		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);
+#endif
+}
+
+#endif /* _LINUX_CMDLINE_H */