[PATCH v3] fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled
Tim Harvey
tharvey at gateworks.com
Tue May 21 22:59:55 CEST 2024
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 at gateworks.com>
Cc: Michal Simek <michal.simek at amd.com>
Cc: Andy Yan <andy.yan at rock-chips.com>
Cc: Akash Gajjar <gajjar04akash at gmail.com>
Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
Cc: Simon Glass <sjg at chromium.org>
Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
Cc: Patrice Chotard <patrice.chotard at foss.st.com>
Cc: Devarsh Thakkar <devarsht at ti.com>
Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
Cc: Hugo Villeneuve <hvilleneuve at dimonoff.com>
Cc: Marek Vasut <marex at denx.de>
Cc: Tom Rini <trini at konsulko.com>
Cc: Chris Morgan <macromorgan at 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");
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 at 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 at 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;
+
+ 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;
+}
--
2.25.1
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