Re: [PATCH v3] fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled

On 5/21/24 22:59, Tim Harvey 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. We skip this if ARMV8_SEC_FIRMWARE_SUPPORT is enabled as it's implementation uses a different source of entropy that is not yet implemented as DM_RNG. We also skip this if MEASURED_BOOT is enabled as in that case any modifications to the dt will cause measured boot to fail (although there are many other places the dt is altered).

As this fdt node is added elsewhere create a library function and use it to deduplicate code. We will provide a parameter to specify the index of the rng device as well as a boolean to overwrite if present.

For our automatic injection, we will use the first rng device and not overwrite if already present with a non-zero value (which may have been populated by an earlier boot stage). This way if a board specific ft_board_setup() function wants to customize this behavior it can call fdt_kaslrseed with a rng device index of its choosing and set overwrite true.

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.

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.

Signed-off-by: Tim Harvey tharvey@gateworks.com Cc: Michal Simek michal.simek@amd.com Cc: Andy Yan andy.yan@rock-chips.com Cc: Akash Gajjar gajjar04akash@gmail.com Cc: Ilias Apalodimas ilias.apalodimas@linaro.org Cc: Simon Glass sjg@chromium.org Cc: Patrick Delaunay patrick.delaunay@foss.st.com Cc: Patrice Chotard patrice.chotard@foss.st.com Cc: Devarsh Thakkar devarsht@ti.com Cc: Heinrich Schuchardt xypron.glpk@gmx.de Cc: Hugo Villeneuve hvilleneuve@dimonoff.com Cc: Marek Vasut marex@denx.de Cc: Tom Rini trini@konsulko.com Cc: Chris Morgan macromorgan@hotmail.com

---

v3:

• skip if CONFIG_MEASURED_BOOT
• fix skip for CONFIG_ARMV8_SEC_FIRMWARE_SUPPORT
• pass in rng index and bool to specify overwrite
• remove duplicate error strings printed outside of fdt_kaslrseed
• added note to commit log about how EFI STUB weeds out kalsr-seed

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 | 6 +++++ boot/pxe_utils.c | 35 ++----------------------- cmd/kaslrseed.c | 45 +++++--------------------------- include/kaslrseed.h | 19 ++++++++++++++ lib/Makefile | 1 + lib/kaslrseed.c | 51 +++++++++++++++++++++++++++++++++++++ 7 files changed, 85 insertions(+), 107 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..b64cdd34825a 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 +301,11 @@ int fdt_chosen(void *fdt) if (nodeoffset < 0) return nodeoffset;

• if (IS_ENABLED(CONFIG_DM_RNG) &&

•    !IS_ENABLED(CONFIG_MEASURED_BOOT) &&
  

•    !IS_ENABLED(CONFIG_ARMV8_SEC_FIRMWARE_SUPPORT))
  

• fdt_kaslrseed(fdt, 0, false);
  

• 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..35d5b9ed3ecc 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 +339,7 @@ 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) {

• printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(err));
  

• goto err;
  

• }

-err:

• free(buf);

• fdt_kaslrseed(working_fdt, 0, true); #endif return; }

diff --git a/cmd/kaslrseed.c b/cmd/kaslrseed.c index e0d3c7fe7489..958ecd8efabb 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");

missing \n here.

if (!working_fdt) { printf("No FDT memory address configured. Please configure\n" @@ -44,27 +27,11 @@ 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, 0, true);
• if (err < 0) 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..7f9911c59fa4 --- /dev/null +++ b/include/kaslrseed.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/*

• • Copyright 2024 Tim Harvey tharvey@gateworks.com
• */

+#if !defined _KASLRSEED_H_ +#define _KASLRSEED_H_

+/**

• • fdt_kaslrseed() - create a 'kaslr-seed' node in chosen
• • @blob: fdt blob
• • @index: index of UCLASS_RNG device to use
• • @overwrite: do not overwrite existing non-zero node unless true
• • Return: 0 if OK, -ve on error
• */

+int fdt_kaslrseed(void *blob, int index, bool overwrite);

+#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..29d7ed2e7718 --- /dev/null +++ b/lib/kaslrseed.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0+ +/*

• • Copyright 2024 Tim Harvey tharvey@gateworks.com
• */

+#include <dm.h> +#include <rng.h> +#include <fdt_support.h> +#include <dm/device_compat.h>

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

• struct udevice *dev;
• const u64 *orig;
• int nodeoffset;
• u64 data = 0;
• int len;
• int err;

nit: you can just use

int len, err, nodeoffset;

• 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;
  

• /* return without error if we are not overwriting and existing non-zero node */
• orig = fdt_getprop(fdt, nodeoffset, "kaslr-seed", &len);
• if (orig && len == sizeof(*orig))

• data = fdt64_to_cpu(*orig);
  

• if (data && !overwrite) {

• debug("not overwriting existing kaslr-seed\n");
  

• return 0;
  

• }
• err = uclass_get_device(UCLASS_RNG, index, &dev);
• if (err) {

• printf("No RNG device at index %d\n", index);
  

• return err;
  

• }
• err = dm_rng_read(dev, &data, sizeof(data));
• if (err) {

• dev_err(dev, "dm_rng_read failed: %d\n", err);
  

• return 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;

+}

Thanks, Michal