[PATCH] mbi: use per segment a separate relocator chunk

[Alexander Boettcher <alexander.boettcher@genode-labs.com>]

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-- 
Alexander Boettcher
Genode Labs

http://www.genode-labs.com - http://www.genode.org

Genode Labs GmbH - Amtsgericht Dresden - HRB 28424 - Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth

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From 8a0296d040a42950cd64e733f7997203975bc184 Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Fri, 13 Apr 2018 23:37:01 +0200
Subject: [PATCH] mbi: use per segment a separate relocator chunk

if elf is non relocatable.

If the segments are not dense packed, the original code set up a huge
relocator chunk comprising all segments.

During the final relocation in grub_relocator_prepare_relocs, the chunk
is moved to its desired place and overrides memory which are actually not
covered/touched by the specified segments.

The overriden memory may contain device memory (vga text mode e.g.), which
leads to strange boot behaviour.

Signed-off-by: Alexander Boettcher <alexander.boettcher@genode-labs.com>
---
 grub-core/loader/multiboot_elfxx.c | 57 +++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/grub-core/loader/multiboot_elfxx.c b/grub-core/loader/multiboot_elfxx.c
index 67daf59..539c94a 100644
--- a/grub-core/loader/multiboot_elfxx.c
+++ b/grub-core/loader/multiboot_elfxx.c
@@ -57,9 +57,9 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
   char *phdr_base;
   grub_err_t err;
   grub_relocator_chunk_t ch;
-  grub_uint32_t load_offset, load_size;
+  grub_uint32_t load_offset = 0, load_size;
   int i;
-  void *source;
+  void *source = NULL;
 
   if (ehdr->e_ident[EI_MAG0] != ELFMAG0
       || ehdr->e_ident[EI_MAG1] != ELFMAG1
@@ -83,6 +83,7 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
 #define phdr(i)			((Elf_Phdr *) (phdr_base + (i) * ehdr->e_phentsize))
 
   mld->link_base_addr = ~0;
+  mld->load_base_addr = ~0;
 
   /* Calculate lowest and highest load address.  */
   for (i = 0; i < ehdr->e_phnum; i++)
@@ -97,10 +98,14 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
     return grub_error (GRUB_ERR_BAD_OS, "segment crosses 4 GiB border");
 #endif
 
-  load_size = highest_load - mld->link_base_addr;
+  grub_dprintf ("multiboot_loader", "link_base_addr=0x%x, load_base_addr=0x%x, "
+		"relocatable=%d\n", mld->link_base_addr,
+		mld->load_base_addr, mld->relocatable);
 
   if (mld->relocatable)
     {
+      load_size = highest_load - mld->link_base_addr;
+
       if (load_size > mld->max_addr || mld->min_addr > mld->max_addr - load_size)
 	return grub_error (GRUB_ERR_BAD_OS, "invalid min/max address and/or load size");
 
@@ -108,27 +113,19 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
 					      mld->min_addr, mld->max_addr - load_size,
 					      load_size, mld->align ? mld->align : 1,
 					      mld->preference, mld->avoid_efi_boot_services);
-    }
-  else
-    err = grub_relocator_alloc_chunk_addr (GRUB_MULTIBOOT (relocator), &ch,
-					   mld->link_base_addr, load_size);
 
-  if (err)
-    {
-      grub_dprintf ("multiboot_loader", "Cannot allocate memory for OS image\n");
-      return err;
-    }
-
-  mld->load_base_addr = get_physical_target_address (ch);
-  source = get_virtual_current_address (ch);
+      if (err)
+        {
+          grub_dprintf ("multiboot_loader", "Cannot allocate memory for OS image\n");
+          return err;
+        }
 
-  grub_dprintf ("multiboot_loader", "link_base_addr=0x%x, load_base_addr=0x%x, "
-		"load_size=0x%x, relocatable=%d\n", mld->link_base_addr,
-		mld->load_base_addr, load_size, mld->relocatable);
+      mld->load_base_addr = get_physical_target_address (ch);
+      source = get_virtual_current_address (ch);
 
-  if (mld->relocatable)
-    grub_dprintf ("multiboot_loader", "align=0x%lx, preference=0x%x, avoid_efi_boot_services=%d\n",
-		  (long) mld->align, mld->preference, mld->avoid_efi_boot_services);
+      grub_dprintf ("multiboot_loader", "align=0x%lx, preference=0x%x, avoid_efi_boot_services=%d\n",
+		     (long) mld->align, mld->preference, mld->avoid_efi_boot_services);
+    }
 
   /* Load every loadable segment in memory.  */
   for (i = 0; i < ehdr->e_phnum; i++)
@@ -139,7 +136,23 @@ CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
 	  grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx, memsz=0x%lx, vaddr=0x%lx\n",
 			i, (long) phdr(i)->p_paddr, (long) phdr(i)->p_memsz, (long) phdr(i)->p_vaddr);
 
-	  load_offset = phdr(i)->p_paddr - mld->link_base_addr;
+	  if (mld->relocatable)
+	    load_offset = phdr(i)->p_paddr - mld->link_base_addr;
+	  else
+	    {
+	      err = grub_relocator_alloc_chunk_addr (GRUB_MULTIBOOT (relocator), &ch,
+	                                             phdr(i)->p_paddr, phdr(i)->p_memsz);
+
+	      if (err)
+		{
+		  grub_dprintf ("multiboot_loader", "Cannot allocate memory for OS image\n");
+		  return err;
+		}
+
+	      mld->load_base_addr = grub_min (mld->load_base_addr, get_physical_target_address (ch));
+
+	      source = get_virtual_current_address (ch);
+	    }
 
 	  if (phdr(i)->p_filesz != 0)
 	    {
-- 
2.7.4