Re: [PATCH v2 1/7] cmdline: Add generic function to build command line.
From: Christophe Leroy
Date: Fri Mar 05 2021 - 07:50:22 EST
Le 05/03/2021 à 12:58, Michael Ellerman a écrit :
Will Deacon <will@xxxxxxxxxx> 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@xxxxxxxxxx>
---
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