Right, this already came up in response to v1.
I think grub is currently safe but after some further digging we might
want to add
support for the DT_FIXUP protocol or similar at some point and this makes things
more complicated than necessary. I'll send another update.
On Mon, Jun 17, 2024 at 3:44 PM Vladimir 'phcoder' Serbinenko
<phco...@gmail.com> wrote:
>
> Saving FDT subtly changes the behaviour. Image some command or even an
> external program modifying FDT and freeing old copy. Maybe we should
> call grub_efi_get_firmware_fdt every time we need fdt.
>
> On Mon, Jun 17, 2024 at 4:08 PM Tobias Heider
> <tobias.hei...@canonical.com> wrote:
> >
> > The fdtdump command allows dumping arbitrary device tree properties
> > and saving them to a variable similar to the smbios command.
> >
> > This is useful in scripts where further actions such as selecting a
> > kernel or loading another device tree depend on the compatible or
> > model values of the device tree provided by the firmware.
> >
> > For now only the root level properties of the dtb are exposed.
> >
> > The firmware provided device-tree is not expected to change so we
> > load it once during module initialization and then use it where
> > needed.
> >
> > Signed-off-by: Tobias Heider <tobias.hei...@canonical.com>
> > ---
> > docs/grub.texi | 26 ++++++++++++++++++++
> > grub-core/loader/efi/fdt.c | 49 +++++++++++++++++++++++++++++++++++++-
> > 2 files changed, 74 insertions(+), 1 deletion(-)
> >
> > diff --git a/docs/grub.texi b/docs/grub.texi
> > index f3bdc2564..a050dc0fc 100644
> > --- a/docs/grub.texi
> > +++ b/docs/grub.texi
> > @@ -4373,6 +4373,7 @@ you forget a command, you can run the command
> > @command{help}
> > * eval:: Evaluate agruments as GRUB commands
> > * export:: Export an environment variable
> > * false:: Do nothing, unsuccessfully
> > +* fdtdump:: Retrieve device tree information
> > * fwsetup:: Reboot into the firmware setup menu
> > * gdbinfo:: Provide info for debugging with GDB
> > * gettext:: Translate a string
> > @@ -4904,6 +4905,31 @@ such as @code{if} and @code{while}
> > (@pxref{Shell-like scripting}).
> > @end deffn
> >
> >
> > +@node fdtdump
> > +@subsection fdtdump
> > +
> > +@deffn Command fdtdump @
> > + [@option{--prop} @var{prop}] @
> > + [@option{--set} @var{variable}]
> > +Retrieve device tree information.
> > +
> > +The @command{fdtdump} command returns the value of a property in the device
> > +tree provided by the firmware. The @option{--prop} option determines which
> > +property to select.
> > +
> > +The default action is to print the value of the requested field to the
> > console,
> > +but a variable name can be specified with @option{--set} to store the value
> > +instead of printing it.
> > +
> > +For example, this will store and then display the model string.
> > +
> > +@example
> > +fdtdump --prop model --set machine_model
> > +echo $machine_model
> > +@end example
> > +@end deffn
> > +
> > +
> > @node fwsetup
> > @subsection fwsetup
> >
> > diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
> > index 439964b9c..cb0422d98 100644
> > --- a/grub-core/loader/efi/fdt.c
> > +++ b/grub-core/loader/efi/fdt.c
> > @@ -1,6 +1,7 @@
> > /*
> > * GRUB -- GRand Unified Bootloader
> > * Copyright (C) 2013-2015 Free Software Foundation, Inc.
> > + * Copyright (C) 2024 Canonical, Ltd.
> > *
> > * GRUB is free software: you can redistribute it and/or modify
> > * it under the terms of the GNU General Public License as published by
> > @@ -18,15 +19,18 @@
> >
> > #include <grub/fdt.h>
> > #include <grub/mm.h>
> > +#include <grub/env.h>
> > #include <grub/err.h>
> > #include <grub/dl.h>
> > #include <grub/command.h>
> > +#include <grub/extcmd.h>
> > #include <grub/file.h>
> > #include <grub/efi/efi.h>
> > #include <grub/efi/fdtload.h>
> > #include <grub/efi/memory.h>
> > #include <grub/cpu/efi/memory.h>
> >
> > +static void *fw_fdt;
> > static void *loaded_fdt;
> > static void *fdt;
> >
> > @@ -36,6 +40,13 @@ static void *fdt;
> > sizeof (FDT_ADDR_CELLS_STRING) + \
> > sizeof (FDT_SIZE_CELLS_STRING))
> >
> > +static const struct grub_arg_option options_fdtdump[] = {
> > + {"prop", 'p', 0, N_("Get property."), N_("prop"), ARG_TYPE_STRING},
> > + {"set", '\0', 0, N_("Store the value in the given variable name."),
> > + N_("variable"), ARG_TYPE_STRING},
> > + {0, 0, 0, 0, 0, 0}
> > +};
> > +
> > void *
> > grub_fdt_load (grub_size_t additional_size)
> > {
> > @@ -51,7 +62,7 @@ grub_fdt_load (grub_size_t additional_size)
> > if (loaded_fdt)
> > raw_fdt = loaded_fdt;
> > else
> > - raw_fdt = grub_efi_get_firmware_fdt();
> > + raw_fdt = fw_fdt;
> >
> > if (raw_fdt)
> > size = grub_fdt_get_totalsize (raw_fdt);
> > @@ -167,10 +178,45 @@ out:
> > return grub_errno;
> > }
> >
> > +static grub_err_t
> > +grub_cmd_fdtdump (grub_extcmd_context_t ctxt,
> > + int argc __attribute__ ((unused)),
> > + char **argv __attribute__ ((unused)))
> > +{
> > + struct grub_arg_list *state = ctxt->state;
> > + const char *value = NULL;
> > +
> > + if (fw_fdt == NULL)
> > + return grub_error (GRUB_ERR_IO,
> > + N_("No device tree found"));
> > +
> > + if (state[0].set)
> > + value = grub_fdt_get_prop (fw_fdt, 0, state[0].arg, NULL);
> > +
> > + if (value == NULL)
> > + return grub_error (GRUB_ERR_OUT_OF_RANGE,
> > + N_("failed to retrieve the prop field"));
> > +
> > + if (state[1].set)
> > + grub_env_set (state[1].arg, value);
> > + else
> > + grub_printf ("%s\n", value);
> > +
> > + return GRUB_ERR_NONE;
> > +}
> > +
> > static grub_command_t cmd_devicetree;
> > +static grub_extcmd_t cmd_fdtdump;
> >
> > GRUB_MOD_INIT (fdt)
> > {
> > + fw_fdt = grub_efi_get_firmware_fdt();
> > +
> > + cmd_fdtdump =
> > + grub_register_extcmd ("fdtdump", grub_cmd_fdtdump, 0,
> > + N_("[-p] [--set variable]"),
> > + N_("Retrieve device tree information."),
> > + options_fdtdump);
> > cmd_devicetree =
> > grub_register_command_lockdown ("devicetree", grub_cmd_devicetree, 0,
> > N_("Load DTB file."));
> > @@ -179,4 +225,5 @@ GRUB_MOD_INIT (fdt)
> > GRUB_MOD_FINI (fdt)
> > {
> > grub_unregister_command (cmd_devicetree);
> > + grub_unregister_extcmd (cmd_fdtdump);
> > }
> > --
> > 2.43.0
> >
> >
> > _______________________________________________
> > Grub-devel mailing list
> > Grub-devel@gnu.org
> > https://lists.gnu.org/mailman/listinfo/grub-devel
>
>
>
> --
> Regards
> Vladimir 'phcoder' Serbinenko
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
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