[PATCH v4] fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled

Michal Simek michal.simek at amd.com
Mon May 27 10:30:32 CEST 2024



On 5/25/24 22:02, 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 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>
> ---
> v4:
>   - add missing /n to notice in kaslrseed cmd
>   - combine ints in declaration
>   - remove unused vars from board/xilinx/common/board.c ft_board_setup
> 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 | 40 ------------------------------
>   boot/fdt_support.c          |  6 +++++
>   boot/pxe_utils.c            | 35 ++------------------------
>   cmd/kaslrseed.c             | 45 +++++-----------------------------
>   include/kaslrseed.h         | 19 ++++++++++++++
>   lib/Makefile                |  1 +
>   lib/kaslrseed.c             | 49 +++++++++++++++++++++++++++++++++++++
>   7 files changed, 83 insertions(+), 112 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..0b43407b9e94 100644
> --- a/board/xilinx/common/board.c
> +++ b/board/xilinx/common/board.c
> @@ -701,11 +701,6 @@ phys_addr_t board_get_usable_ram_top(phys_size_t total_size)
>   #define MAX_RAND_SIZE 8
>   int ft_board_setup(void *blob, struct bd_info *bd)
>   {
> -	size_t n = MAX_RAND_SIZE;
> -	struct udevice *dev;
> -	u8 buf[MAX_RAND_SIZE];
> -	int nodeoffset, ret;
> -
>   	static const struct node_info nodes[] = {
>   		{ "arm,pl353-nand-r2p1", MTD_DEV_TYPE_NAND, },
>   	};
> @@ -713,41 +708,6 @@ 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..ebe4058d7ac6 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\n");
>   
>   	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;

You should consider to use standard function here.
return cmd_process_error(cmdtp, err);

Anyway looks good to me.
Acked-by: Michal Simek <michal.simek at amd.com>
Tested-by: Michal Simek <michal.simek at amd.com> # ZynqMP Kria

Thanks,
Michal


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