Will Deacon <w...@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.le...@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