Re: [PATCH] ieee1275: Use net config for boot location instead of firmware bootpath

* [PATCH] ieee1275: Use net config for boot location instead of firmware bootpath
@ 2025-10-13  6:52 Michael Chang via Grub-devel
  2025-10-15 14:08 ` Daniel Kiper
  0 siblings, 1 reply; 3+ messages in thread
From: Michael Chang via Grub-devel @ 2025-10-13  6:52 UTC (permalink / raw)
  To: The development of GNU GRUB; +Cc: Michael Chang

On network boots, grub_ieee1275_net_config() is used to determine the
boot device, but the path continues to be taken from the Open Firmware
/chosen/bootpath property. This assumes the device node follows the
generic IEEE-1275 syntax, which is not always the case. Different
drivers may extend or redefine the format, and GRUB may then
misinterpret the argument as a filename and set $prefix incorrectly.

The generic Open Firmware device path format is:

  device-name[:device-argument]
  device-argument := [partition][,[filename]]

For example, a bootpath such as:

  /vdevice/l-lan@30000002:speed=auto,duplex=auto,1.2.243.345,,9.8.76.543,1.2.34.5,5,5,255.255.255.0,512

does not follow this form. The section after the colon (the
device-argument) contains driver-specific options and network
parameters, not a valid filename. GRUB interprets this string as a
filename, which results in $prefix being set to "/", effectively losing
the intended boot directory.

The firmware is not at fault here, since interpretation of device nodes
is driver-specific. Instead, GRUB should use the filename provided in
the cached DHCP packet, which is consistent and reliable. This is also
the same mechanism already used on UEFI and legacy BIOS platforms.

This patch updates grub_machine_get_bootlocation() to prefer the result
from grub_ieee1275_net_config() when complete, and only fall back to the
firmware bootpath otherwise.

Signed-off-by: Michael Chang <mchang@suse.com>
---
 grub-core/kern/ieee1275/init.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index a5586f85b..8893a881d 100644
--- a/grub-core/kern/ieee1275/init.c
+++ b/grub-core/kern/ieee1275/init.c
@@ -149,9 +149,11 @@ void (*grub_ieee1275_net_config) (const char *dev, char **device, char **path,
 void
 grub_machine_get_bootlocation (char **device, char **path)
 {
-  char *bootpath;
+  char *bootpath = NULL;
   char *filename;
-  char *type;
+  char *type = NULL;
+  char *ret_device = NULL;
+  char *ret_path = NULL;
 
   bootpath = grub_ieee1275_get_boot_dev ();
   if (! bootpath)
@@ -167,7 +169,7 @@ grub_machine_get_bootlocation (char **device, char **path)
       dev = grub_ieee1275_get_aliasdevname (bootpath);
       canon = grub_ieee1275_canonicalise_devname (dev);
       if (! canon)
-        return;
+	goto done;
       ptr = canon + grub_strlen (canon) - 1;
       while (ptr > canon && (*ptr == ',' || *ptr == ':'))
 	ptr--;
@@ -175,13 +177,17 @@ grub_machine_get_bootlocation (char **device, char **path)
       *ptr = 0;
 
       if (grub_ieee1275_net_config)
-	grub_ieee1275_net_config (canon, device, path, bootpath);
+	grub_ieee1275_net_config (canon, &ret_device, &ret_path, bootpath);
       grub_free (dev);
       grub_free (canon);
+
+      /* Use path from net config if it is provided by cached DHCP info */
+      if (ret_path != NULL)
+	goto done;
+      /* Fall through to use firmware bootpath */
     }
   else
-    *device = grub_ieee1275_encode_devname (bootpath);
-  grub_free (type);
+    ret_device = grub_ieee1275_encode_devname (bootpath);
 
   filename = grub_ieee1275_get_filename (bootpath);
   if (filename)
@@ -194,10 +200,18 @@ grub_machine_get_bootlocation (char **device, char **path)
 	  *lastslash = '\0';
 	  grub_translate_ieee1275_path (filename);
 
-	  *path = filename;
+	  ret_path = filename;
 	}
     }
+
+ done:
+  grub_free (type);
   grub_free (bootpath);
+
+  if (device != NULL)
+    *device = ret_device;
+  if (path != NULL)
+    *path = ret_path;
 }
 
 /* Claim some available memory in the first /memory node. */
-- 
2.51.0


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