[PATCH v2] fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled

Tim Harvey tharvey at gateworks.com
Tue May 21 18:36:48 CEST 2024


On Tue, May 21, 2024 at 5:05 AM Ilias Apalodimas
<ilias.apalodimas at linaro.org> wrote:
>
> Hi Tim
>
> On Wed, 15 May 2024 at 23:50, Tim Harvey <tharvey at gateworks.com> wrote:
> >
> > If RANDOMIZE_BASE is enabled in the Linux kernel instructing it to
> > randomize the virtual address at which the kernel image is loaded, it
> > expects entropy to be provided by the bootloader by populating
> > /chosen/kaslr-seed with a 64-bit value from source of entropy at boot.
>
> Since you'll send a v2, mind adding some description for UEFI on the
> commit message?
> efi_try_purge_kaslr_seed() has a comment of the behaviour
>

Hi  Ilias,

Ok, I will add the following to the commit log for clarity:
Note that the Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for
randomization and completely ignores the kaslr-seed for its own
randomness needs (i.e the randomization of the physical placement of
the kernel). It gets weeded out from the DTB that gets handed over via
efi_install_fdt() as it would also mess up the measured boot DTB TPM
measurements as well.

Does the above mean that I don't need to worry about protecting the
call to fdt_kaslrseed() with a check for MEASURED BOOT as
efi_install_fdt/efi_try_purge_kaslr_seed always gets called in that
case?

Best Regards,

Tim

> Thanks
> /Ilias
> >
> > If we have DM_RNG enabled populate this value automatically when
> > fdt_chosen is called unless ARMV8_SEC_FIRMWARE_SUPPORT is enabled as
> > it's implementation uses a different source of entropy.
> >
> > As this fdt node is added elsewhere create a library function and
> > use it to deduplicate code.
> >
> > Note that the kalsrseed command (CMD_KASLRSEED) is likely pointless now
> > but left in place in case boot scripts exist that rely on this command
> > existing and returning success. An informational message is printed to
> > alert users of this command that it is likely no longer needed.
> >
> > Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> > ---
> > v2:
> >  - fix typo in commit msg
> >  - use stack for seed to avoid unecessary malloc/free
> >  - move to a library function and deduplicate code by using it elsewhere
> > ---
> >  board/xilinx/common/board.c | 35 -----------------------------
> >  boot/fdt_support.c          | 10 +++++++++
> >  boot/pxe_utils.c            | 35 +++--------------------------
> >  cmd/kaslrseed.c             | 45 ++++++-------------------------------
> >  include/kaslrseed.h         | 17 ++++++++++++++
> >  lib/Makefile                |  1 +
> >  lib/kaslrseed.c             | 34 ++++++++++++++++++++++++++++
> >  7 files changed, 72 insertions(+), 105 deletions(-)
> >  create mode 100644 include/kaslrseed.h
> >  create mode 100644 lib/kaslrseed.c
> >
> > diff --git a/board/xilinx/common/board.c b/board/xilinx/common/board.c
> > index 30a81376ac41..f741e8957818 100644
> > --- a/board/xilinx/common/board.c
> > +++ b/board/xilinx/common/board.c
> > @@ -713,41 +713,6 @@ int ft_board_setup(void *blob, struct bd_info *bd)
> >         if (IS_ENABLED(CONFIG_FDT_FIXUP_PARTITIONS) && IS_ENABLED(CONFIG_NAND_ZYNQ))
> >                 fdt_fixup_mtdparts(blob, nodes, ARRAY_SIZE(nodes));
> >
> > -       if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > -               debug("No RNG device\n");
> > -               return 0;
> > -       }
> > -
> > -       if (dm_rng_read(dev, buf, n)) {
> > -               debug("Reading RNG failed\n");
> > -               return 0;
> > -       }
> > -
> > -       if (!blob) {
> > -               debug("No FDT memory address configured. Please configure\n"
> > -                     "the FDT address via \"fdt addr <address>\" command.\n"
> > -                     "Aborting!\n");
> > -               return 0;
> > -       }
> > -
> > -       ret = fdt_check_header(blob);
> > -       if (ret < 0) {
> > -               debug("fdt_chosen: %s\n", fdt_strerror(ret));
> > -               return ret;
> > -       }
> > -
> > -       nodeoffset = fdt_find_or_add_subnode(blob, 0, "chosen");
> > -       if (nodeoffset < 0) {
> > -               debug("Reading chosen node failed\n");
> > -               return nodeoffset;
> > -       }
> > -
> > -       ret = fdt_setprop(blob, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > -       if (ret < 0) {
> > -               debug("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(ret));
> > -               return ret;
> > -       }
> > -
> >         return 0;
> >  }
> >  #endif
> > diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> > index 874ca4d6f5af..3455d60d69dc 100644
> > --- a/boot/fdt_support.c
> > +++ b/boot/fdt_support.c
> > @@ -8,6 +8,7 @@
> >
> >  #include <abuf.h>
> >  #include <env.h>
> > +#include <kaslrseed.h>
> >  #include <log.h>
> >  #include <mapmem.h>
> >  #include <net.h>
> > @@ -300,6 +301,15 @@ int fdt_chosen(void *fdt)
> >         if (nodeoffset < 0)
> >                 return nodeoffset;
> >
> > +       if (IS_ENABLED(CONFIG_DM_RNG) && !IS_ENABLED(ARMV8_SEC_FIRMWARE_SUPPORT)) {
> > +               err = fdt_kaslrseed(fdt);
> > +               if (err) {
> > +                       printf("WARNING: could not set kaslr-seed %s.\n",
> > +                              fdt_strerror(err));
> > +                       return err;
> > +               }
> > +       }
> > +
> >         if (IS_ENABLED(CONFIG_BOARD_RNG_SEED) && !board_rng_seed(&buf)) {
> >                 err = fdt_setprop(fdt, nodeoffset, "rng-seed",
> >                                   abuf_data(&buf), abuf_size(&buf));
> > diff --git a/boot/pxe_utils.c b/boot/pxe_utils.c
> > index 4b22bb6f525a..8d70233fc08d 100644
> > --- a/boot/pxe_utils.c
> > +++ b/boot/pxe_utils.c
> > @@ -8,6 +8,7 @@
> >  #include <dm.h>
> >  #include <env.h>
> >  #include <image.h>
> > +#include <kaslrseed.h>
> >  #include <log.h>
> >  #include <malloc.h>
> >  #include <mapmem.h>
> > @@ -323,10 +324,6 @@ static void label_boot_kaslrseed(void)
> >  #if CONFIG_IS_ENABLED(DM_RNG)
> >         ulong fdt_addr;
> >         struct fdt_header *working_fdt;
> > -       size_t n = 0x8;
> > -       struct udevice *dev;
> > -       u64 *buf;
> > -       int nodeoffset;
> >         int err;
> >
> >         /* Get the main fdt and map it */
> > @@ -342,35 +339,9 @@ static void label_boot_kaslrseed(void)
> >         if (err <= 0)
> >                 return;
> >
> > -       if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > -               printf("No RNG device\n");
> > -               return;
> > -       }
> > -
> > -       nodeoffset = fdt_find_or_add_subnode(working_fdt, 0, "chosen");
> > -       if (nodeoffset < 0) {
> > -               printf("Reading chosen node failed\n");
> > -               return;
> > -       }
> > -
> > -       buf = malloc(n);
> > -       if (!buf) {
> > -               printf("Out of memory\n");
> > -               return;
> > -       }
> > -
> > -       if (dm_rng_read(dev, buf, n)) {
> > -               printf("Reading RNG failed\n");
> > -               goto err;
> > -       }
> > -
> > -       err = fdt_setprop(working_fdt, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > -       if (err < 0) {
> > +       err = fdt_kaslrseed(working_fdt);
> > +       if (err < 0)
> >                 printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(err));
> > -               goto err;
> > -       }
> > -err:
> > -       free(buf);
> >  #endif
> >         return;
> >  }
> > diff --git a/cmd/kaslrseed.c b/cmd/kaslrseed.c
> > index e0d3c7fe7489..ea5c07d729cf 100644
> > --- a/cmd/kaslrseed.c
> > +++ b/cmd/kaslrseed.c
> > @@ -9,33 +9,16 @@
> >  #include <command.h>
> >  #include <dm.h>
> >  #include <hexdump.h>
> > +#include <kaslrseed.h>
> >  #include <malloc.h>
> >  #include <rng.h>
> >  #include <fdt_support.h>
> >
> >  static int do_kaslr_seed(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
> >  {
> > -       size_t n = 0x8;
> > -       struct udevice *dev;
> > -       u64 *buf;
> > -       int nodeoffset;
> > -       int ret = CMD_RET_SUCCESS;
> > +       int err;
> >
> > -       if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > -               printf("No RNG device\n");
> > -               return CMD_RET_FAILURE;
> > -       }
> > -
> > -       buf = malloc(n);
> > -       if (!buf) {
> > -               printf("Out of memory\n");
> > -               return CMD_RET_FAILURE;
> > -       }
> > -
> > -       if (dm_rng_read(dev, buf, n)) {
> > -               printf("Reading RNG failed\n");
> > -               return CMD_RET_FAILURE;
> > -       }
> > +       printf("Notice: a /chosen/kaslr-seed is automatically added to the device-tree when booted via booti/bootm/bootz therefore using this command is likely no longer needed");
> >
> >         if (!working_fdt) {
> >                 printf("No FDT memory address configured. Please configure\n"
> > @@ -44,27 +27,13 @@ static int do_kaslr_seed(struct cmd_tbl *cmdtp, int flag, int argc, char *const
> >                 return CMD_RET_FAILURE;
> >         }
> >
> > -       ret = fdt_check_header(working_fdt);
> > -       if (ret < 0) {
> > -               printf("fdt_chosen: %s\n", fdt_strerror(ret));
> > +       err = fdt_kaslrseed(working_fdt);
> > +       if (err < 0) {
> > +               printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(err));
> >                 return CMD_RET_FAILURE;
> >         }
> >
> > -       nodeoffset = fdt_find_or_add_subnode(working_fdt, 0, "chosen");
> > -       if (nodeoffset < 0) {
> > -               printf("Reading chosen node failed\n");
> > -               return CMD_RET_FAILURE;
> > -       }
> > -
> > -       ret = fdt_setprop(working_fdt, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > -       if (ret < 0) {
> > -               printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(ret));
> > -               return CMD_RET_FAILURE;
> > -       }
> > -
> > -       free(buf);
> > -
> > -       return ret;
> > +       return CMD_RET_SUCCESS;
> >  }
> >
> >  U_BOOT_LONGHELP(kaslrseed,
> > diff --git a/include/kaslrseed.h b/include/kaslrseed.h
> > new file mode 100644
> > index 000000000000..3fe82f418acf
> > --- /dev/null
> > +++ b/include/kaslrseed.h
> > @@ -0,0 +1,17 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> > +/*
> > + * Copyright 2024 Tim Harvey <tharvey at gateworks.com>
> > + */
> > +
> > +#if !defined _KASLRSEED_H_
> > +#define _KASLRSEED_H_
> > +
> > +/**
> > + * fdt_kaslrseed() - create a 'kaslr-seed' node in chosen
> > + *
> > + * @blob:      fdt blob
> > + * Return:     0 if OK, -ve on error
> > + */
> > +int fdt_kaslrseed(void *blob);
> > +
> > +#endif /* _KASLRSEED_H_ */
> > diff --git a/lib/Makefile b/lib/Makefile
> > index 2a76acf100d0..20a0242055fa 100644
> > --- a/lib/Makefile
> > +++ b/lib/Makefile
> > @@ -149,6 +149,7 @@ obj-y += date.o
> >  obj-y += rtc-lib.o
> >  obj-$(CONFIG_LIB_ELF) += elf.o
> >
> > +obj-$(CONFIG_DM_RNG) += kaslrseed.o
> >  obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
> >
> >  #
> > diff --git a/lib/kaslrseed.c b/lib/kaslrseed.c
> > new file mode 100644
> > index 000000000000..ad06bee2b88d
> > --- /dev/null
> > +++ b/lib/kaslrseed.c
> > @@ -0,0 +1,34 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Copyright 2024 Tim Harvey <tharvey at gateworks.com>
> > + */
> > +#include <dm.h>
> > +#include <rng.h>
> > +#include <fdt_support.h>
> > +
> > +int fdt_kaslrseed(void *fdt)
> > +{
> > +       struct udevice *dev;
> > +       int nodeoffset;
> > +       u64 data;
> > +       int err;
> > +
> > +       err = fdt_check_header(fdt);
> > +       if (err < 0)
> > +               return err;
> > +
> > +       /* find or create "/chosen" node. */
> > +       nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen");
> > +       if (nodeoffset < 0)
> > +               return nodeoffset;
> > +
> > +       err = uclass_get_device(UCLASS_RNG, 0, &dev);
> > +       if (!err)
> > +               err = dm_rng_read(dev, &data, sizeof(data));
> > +       if (!err)
> > +               err = fdt_setprop(fdt, nodeoffset, "kaslr-seed", &data, sizeof(data));
> > +       if (err < 0)
> > +               printf("WARNING: could not set kaslr-seed %s.\n", fdt_strerror(err));
> > +
> > +       return err;
> > +}
> > --
> > 2.25.1
> >


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