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

[Michal Simek]

On 5/20/24 18:37, Tim Harvey wrote:
On Mon, May 20, 2024 at 1:29 AM Michal Simek <michal.si...@amd.com> wrote:

Hi Tim,

On 5/16/24 17:58, Tim Harvey wrote:
On Wed, May 15, 2024 at 1:50 PM Tim Harvey <thar...@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.

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 <thar...@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 <thar...@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 <thar...@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));

I have used debug messages to better track if error happens. I think it would be
good if you can extend your code with it.
Because if this fails people have to start tracking if issue is that there is
RNG device or reading fails or issue with setting up property.

Hi Michal,

I'm assuming there is no valid case to have DM_RNG enabled and no
UCLASS_RNG driver which is why I'm printing an error if it ultimately
fails (vs a silent debug statement). If that is true then I should
probably printf errors for all the cases above vs debugs wouldn't you
think?

You can have RNG in SOC or you can have RNG inside TPM for example.
It means DM_RNG can be enabled with two drivers but spi/i2c don't need to work 
and access to internal RNG doesn't need to be permitted.
debug() messages are not going to production systems but having them rightly 
written can help with debugging issues without writing own debug messsages.




In v1 it was said that you won't update it if the kaslr-seed property exists.
I can't see this in the code. Or do I read it incorrectly?


That was a question posed in the discussion but I didn't get an answer
if that was what I should do. None of the three places I'm
deduplicating the functionality from check to see if it already
exists... they would overwrite an existing one. Is there a valid case
where you would not want to overwrite it?

In production system very likely not but I can imagine that developers can play 
with it.

+
+       return err;
+}
--
2.25.1


I realized I forgot a few CC's here. Adding:

Michal Simek <michal.si...@amd.com> (board/xilinx/common/board.c and
configs/xilinx* which have CMD_KASLRSEED)
Andy Yan <andy....@rock-chips.com> (configs/evb-rk3308_defconfig and
configs/roc-cc-rk3308_defconfig which have CMD_KASLRSEED)
Akash Gajjar <gajjar04ak...@gmail.com>
(configs/rock-pi-s-rk3308_defconfig which has CMD_KASLRSEED)
Ilias Apalodimas <ilias.apalodi...@linaro.org> (MEASURE_DEVICETREE,
MEASURED_BOOT)

Michal, I see that board/xilinx/common/board.c is adding
chosen/kaslr-seed in ft_board_setup as well as some of the
configs/xilinx boards enabling CMD_KASLRSEED - can we remove
CMD_ASLRSEED from those boards? (ie no bootscripts require it?)


Based on my note above that you shouldn't change kaslr-seed if exists.

I can add that if you think it's the correct behavior, but that is not
what is done in the current code.

yes I know



What would also make sense is to extend kaslrseed command to pass one more
parameter to pass which RNG instance should generate data on system with more
RNGs. Then pretty much with command you can choose different RNG because current
code hardcoded it to instance 0.

Do you mean extend the command or the fdt_kaslrseed function? I'm
trying to obsolete the command.

I am fully aware about this.


I can add an index to fdt_kaslrseed but would it be more useful to add
a udevice* that is used unless null? I can't see where someone wanting
to call this function would know the index of a specific UCLASS_RNG
device and not have the device * handy instead.

Think about system as I described above with two RNGs in the system.
How do you provide a way to select which one is going to be used?
Index 0 means the first device which is bind. What user should do if they want 
to use the second device? Resort DT?
Use RNG DT aliases or so?


It sounds like with the question of not overwriting an existing value
you are anticipating board specific ft_board_setup functions that may
want to behave differently and choose a different rng source? If so,
ft_board_setup is called 'after' fdt_chosen so maybe fdt_kaslrseed
also needs a boolean to tell it to overwrite existing?

This sounds good to me.

It means pretty much if you can change it to

int fdt_kaslrseed(void *fdt, int index, bool overwrite)

where generic call will call index as 0 and if users want to overwrite it they 
can. Default value for overwrite is tricky because I can understand setting it 
to both values.



Are you open to removing CMD_KASLRSEED from the configs/xilinx* which
have it? If I can get everyone's approval for the few boards that
include CMD_KASLRSEED I would like to remove the command if we are
doing it automatically.

I think command itself can provide an easy way how to inject kaslr-seed to DT 
from other RNGs but also your current implementation takes care about DT used 
for booting one OS. I am not playing with Dom0-less systems but I can imagine 
that there could be a need to inject more then just one seed for other CPUs on 
heterogenios systems that's why I wouldn't really force to remove the command.
If people don't like they can simply disable it.


(adding Chris Morgan <macromor...@hotmail.com> to cc who authored that cmd)


Do you have correct dependency in generic code when MEASURED_BOOT is enabled as
was mentioned in v1? If yes it should be mentioned in commit message.


Likely something is needed but I'm not sure if it's MEASURED_BOOT or
MEASURE_DEVICETREE - That's a question I posed to Ilias.

Ilias was at Linaro connect. When he gets back he will likely answer it.

Thanks,
Michal