[PATCH] [v4] cmd: pxe_utils: sysboot: add kaslr-seed generation support

[Zhang Ning]

this will add kaslrseed keyword to sysboot lable,
when it set, it will request to genarate random number
from hwrng as kaslr-seed.

with this patch exlinux.conf label looks like

label l0
        menu testing
        linux /boot/vmlinuz-5.15.16-arm
        initrd /boot/initramfs-5.15.16-arm.img
        fdtdir /boot/dtbs/5.15.16-arm/
        kaslrseed
        append root=UUID=92ae1e50-eeeb-4c5b-8939-7e1cd6cfb059 ro

Tested on Khadas VIM with kernel 5.16.0-rc5-arm64, Debian 11.

Signed-off-by: Zhang Ning <zhangn1985 at qq.com>
---
 boot/pxe_utils.c    | 75 +++++++++++++++++++++++++++++++++++++++++++++
 doc/README.pxe      |  2 ++
 include/pxe_utils.h |  2 ++
 3 files changed, 79 insertions(+)

diff --git a/boot/pxe_utils.c b/boot/pxe_utils.c
index bb231b11a2..0c24becae3 100644
--- a/boot/pxe_utils.c
+++ b/boot/pxe_utils.c
@@ -20,6 +20,11 @@
 #include <errno.h>
 #include <linux/list.h>
 
+#ifdef CONFIG_DM_RNG
+#include <dm.h>
+#include <rng.h>
+#endif
+
 #include <splash.h>
 #include <asm/io.h>
 
@@ -311,6 +316,67 @@ static int label_localboot(struct pxe_label *label)
 	return run_command_list(localcmd, strlen(localcmd), 0);
 }
 
+/*
+ * label_boot_kaslrseed generate kaslrseed from hw rng
+ */
+
+static void label_boot_kaslrseed(void)
+{
+#ifdef CONFIG_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 */
+	fdt_addr = hextoul(env_get("fdt_addr_r"), NULL);
+	working_fdt = map_sysmem(fdt_addr, 0);
+	err = fdt_check_header(working_fdt);
+	if (err)
+		return;
+
+	/* add extra size for holding kaslr-seed */
+	/* err is new fdt size, 0 or negtive */
+	err = fdt_shrink_to_minimum(working_fdt, 512);
+	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);
+#endif
+	return;
+}
+
 /**
  * label_boot_fdtoverlay() - Loads fdt overlays specified in 'fdtoverlays'
  *
@@ -631,6 +697,9 @@ static int label_boot(struct pxe_context *ctx, struct pxe_label *label)
 				}
 			}
 
+		if (label->kaslrseed)
+			label_boot_kaslrseed();
+
 #ifdef CONFIG_OF_LIBFDT_OVERLAY
 			if (label->fdtoverlays)
 				label_boot_fdtoverlay(ctx, label);
@@ -710,6 +779,7 @@ enum token_type {
 	T_ONTIMEOUT,
 	T_IPAPPEND,
 	T_BACKGROUND,
+	T_KASLRSEED,
 	T_INVALID
 };
 
@@ -741,6 +811,7 @@ static const struct token keywords[] = {
 	{"ontimeout", T_ONTIMEOUT,},
 	{"ipappend", T_IPAPPEND,},
 	{"background", T_BACKGROUND,},
+	{"kaslrseed", T_KASLRSEED,},
 	{NULL, T_INVALID}
 };
 
@@ -1194,6 +1265,10 @@ static int parse_label(char **c, struct pxe_menu *cfg)
 			err = parse_integer(c, &label->ipappend);
 			break;
 
+		case T_KASLRSEED:
+			label->kaslrseed = 1;
+			break;
+
 		case T_EOL:
 			break;
 
diff --git a/doc/README.pxe b/doc/README.pxe
index a1f0423adb..75caa01c4a 100644
--- a/doc/README.pxe
+++ b/doc/README.pxe
@@ -163,6 +163,8 @@ fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
                       and then applied in the load order to the fdt blob stored at the
                       address indicated in the fdt_addr_r environment variable.
 
+kaslrseed           - set this label to request random number from hwrng as kaslr seed.
+
 append <string>	    - use <string> as the kernel command line when booting this
 		      label.
 
diff --git a/include/pxe_utils.h b/include/pxe_utils.h
index dad2668818..4a73b2aace 100644
--- a/include/pxe_utils.h
+++ b/include/pxe_utils.h
@@ -33,6 +33,7 @@
  * initrd - path to the initrd to use for this label.
  * attempted - 0 if we haven't tried to boot this label, 1 if we have.
  * localboot - 1 if this label specified 'localboot', 0 otherwise.
+ * kaslrseed - 1 if generate kaslrseed from hw_rng
  * list - lets these form a list, which a pxe_menu struct will hold.
  */
 struct pxe_label {
@@ -50,6 +51,7 @@ struct pxe_label {
 	int attempted;
 	int localboot;
 	int localboot_val;
+	int kaslrseed;
 	struct list_head list;
 };
 
-- 
2.34.1