Blame SOURCES/0487-powerpc-adjust-setting-of-prefix-for-signed-binary-c.patch

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Mon, 19 Jul 2021 14:35:55 +1000
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Subject: [PATCH] powerpc: adjust setting of prefix for signed binary case
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On RHEL-signed powerpc grub, we sign a grub with -p /grub2 and expect
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that there's a boot partition.
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Unfortunately grub_set_prefix_and_root tries to convert this to
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($fwdevice)/grub2. This ends up being (ieee1275/disk)/grub2 and that
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falls apart pretty quickly - there's no file-system on ieee1275/disk,
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and it makes the search routine try things like
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(ieee1275/disk,msdos2)(ieee1275/disk)/grub2 which also doesn't work.
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Detect if we would be about to create (ieee1275/disk)/path and don't:
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preserve a prefix of /path instead and hope the search later finds us.
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Related: rhbz#1899864
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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---
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 grub-core/kern/main.c | 38 +++++++++++++++++++++++++++++++++-----
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 1 file changed, 33 insertions(+), 5 deletions(-)
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diff --git a/grub-core/kern/main.c b/grub-core/kern/main.c
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index 9bf6a8b231a..25dbcfef1f6 100644
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--- a/grub-core/kern/main.c
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+++ b/grub-core/kern/main.c
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@@ -215,13 +215,41 @@ grub_set_prefix_and_root (void)
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   if (device)
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     {
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       char *prefix_set;
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-    
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-      prefix_set = grub_xasprintf ("(%s)%s", device, path ? : "");
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-      if (prefix_set)
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+
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+#ifdef __powerpc__
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+      /* We have to be careful here on powerpc-ieee1275 + signed grub. We
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+	 will have signed something with a prefix that doesn't have a device
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+	 because we cannot know in advance what partition we're on.
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+
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+	 We will have had !device earlier, so we will have set device=fwdevice
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+	 However, we want to make sure we do not end up setting prefix to be
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+	 ($fwdevice)/path, because we will then end up trying to boot or search
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+	 based on a prefix of (ieee1275/disk)/path, which will not work because
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+	 it's missing a partition.
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+
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+	 Also:
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+	  - You can end up with a device with an FS directly on it, without
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+	    a partition, e.g. ieee1275/cdrom.
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+
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+	  - powerpc-ieee1275 + grub-install sets e.g. prefix=(,gpt2)/path,
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+	    which will have now been extended to device=$fwdisk,partition
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+	    and path=/path
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+
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+	 So we only need to act if device = ieee1275/disk exactly.
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+       */
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+      if (grub_strncmp (device, "ieee1275/disk", 14) == 0)
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+        grub_env_set ("prefix", path);
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+      else
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+#endif
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 	{
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-	  grub_env_set ("prefix", prefix_set);
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-	  grub_free (prefix_set);
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+	  prefix_set = grub_xasprintf ("(%s)%s", device, path ? : "");
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+	  if (prefix_set)
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+	  {
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+	    grub_env_set ("prefix", prefix_set);
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+	    grub_free (prefix_set);
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+	  }
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 	}
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+
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       grub_env_set ("root", device);
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     }
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