[PATCH v3 1/4] qemu: overlay signature nodes

[Ludwig Nussel]

The keys trusted for FIT signature verification are supposed to be
embedded in the device tree built into u-boot. When running in Qemu it's
convenient to use the device tree provided by the VM which doesn't know
about signatures though. So merge both device trees at startup.

Signed-off-by: Ludwig Nussel <ludwig.nussel at siemens.com>

---

Changes in v3:
- enable CONFIG_OF_OMIT_DTB=n in defconfig
- add error returns
- document decission about dt merging direction

 board/emulation/qemu-arm/qemu-arm.c | 50 +++++++++++++++++++++++++++--
 configs/qemu_arm64_defconfig        |  1 +
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
index 38f0ec5f2fb..f82bc81f4d5 100644
--- a/board/emulation/qemu-arm/qemu-arm.c
+++ b/board/emulation/qemu-arm/qemu-arm.c
@@ -144,12 +144,56 @@ int dram_init_banksize(void)
 	return 0;
 }
 
+/* QEMU loads a generated DTB for us at the start of RAM.
+ * When using signatures we may have a built-in FDT that contains our known
+ * public keys nevertheless. So merge those nodes into QEMU's FDT.
+ * We cannot merge the other way around (eg in fdtdec_board_setup()
+ * or board_fix_fdt() at this stage as U-Boot might be started from
+ * a ROM location.
+ * At the same time U-Boot needs QEMU's FDT to initialize serial
+ * devices even before relocation.
+ */
 int board_fdt_blob_setup(void **fdtp)
 {
-	/* QEMU loads a generated DTB for us at the start of RAM. */
-	*fdtp = (void *)CFG_SYS_SDRAM_BASE;
+	void *qemu_fdt = (void *)CFG_SYS_SDRAM_BASE;
+	int ret = -EINVAL;
 
-	return 0;
+	if (fdt_check_header(qemu_fdt) != 0) {
+		log_err("Invalid QEMU FDT at %p\n", qemu_fdt);
+		goto out;
+	}
+
+	if (fdt_check_header(*fdtp) != 0) {
+		/* this was a perfectly normal condition before
+		 * (CONFIG_OF_OMIT_DTB was set for qemu). So to avoid
+		 * breaking existing configs don't error out. This
+		 * might mean that we don't have keys in case
+		 * FIT_SIGNATURE is on. We can't know though as
+		 * existing setups might have injected them into
+		 * QEMUS's FDT already.
+		 */
+		ret = 0;
+		goto out;
+	}
+
+	log_debug("Found built-in FDT at %p. Merging into %p...\n", *fdtp, qemu_fdt);
+
+	ret = fdt_increase_size(qemu_fdt, 1024 + fdt_totalsize(*fdtp));
+	if (ret) {
+		log_err("Failed to resize FDT overlay: %s", fdt_strerror(ret));
+		goto out;
+	}
+
+	ret = fdt_overlay_apply_node(qemu_fdt, 0, (void *)*fdtp, 0);
+	if (ret) {
+		log_err("Failed to apply FDT overlay: %s\n", fdt_strerror(ret));
+		goto out;
+	}
+
+out:
+	*fdtp = qemu_fdt;
+
+	return ret;
 }
 
 void enable_caches(void)
diff --git a/configs/qemu_arm64_defconfig b/configs/qemu_arm64_defconfig
index 68b80e28746..0edf80b7aaa 100644
--- a/configs/qemu_arm64_defconfig
+++ b/configs/qemu_arm64_defconfig
@@ -7,6 +7,7 @@ CONFIG_ENV_SIZE=0x40000
 CONFIG_ENV_SECT_SIZE=0x40000
 CONFIG_DEFAULT_DEVICE_TREE="qemu-arm64"
 CONFIG_OF_LIBFDT_OVERLAY=y
+CONFIG_OF_OMIT_DTB=n
 CONFIG_SYS_LOAD_ADDR=0x40200000
 CONFIG_DEBUG_UART_BASE=0x9000000
 CONFIG_DEBUG_UART_CLOCK=0
-- 
2.43.0