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[PATCH v2] multiboot2: set min address for mbi allocation to 0x1000

From: Lukasz Hawrylko
Subject: [PATCH v2] multiboot2: set min address for mbi allocation to 0x1000
Date: Mon, 16 Dec 2019 11:15:55 +0100

In some cases GRUB2 allocates multiboot2 structure at 0 address, that is
a confusing behavior. Consumers of that structure can have internal NULL-checks
that will throw an error when get a pointer to data allocated at address 0.
To prevent that, define min address for mbi allocation in x86 and x86_64

Signed-off-by: Lukasz Hawrylko <address@hidden>
Reviewed-by: Daniel Kiper <address@hidden>
 grub-core/loader/multiboot_mbi2.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/grub-core/loader/multiboot_mbi2.c 
index 53da78615..18e766c7b 100644
--- a/grub-core/loader/multiboot_mbi2.c
+++ b/grub-core/loader/multiboot_mbi2.c
@@ -48,6 +48,12 @@
 #define HAS_VGA_TEXT 0
+#if defined (__i386__) || defined (__x86_64__)
+#define MBI_MIN_ADDR 0x1000
+#define MBI_MIN_ADDR 0
 struct module
   struct module *next;
@@ -708,7 +714,7 @@ grub_multiboot2_make_mbi (grub_uint32_t *target)
   COMPILE_TIME_ASSERT (MULTIBOOT_TAG_ALIGN % sizeof (grub_properly_aligned_t) 
== 0);
   err = grub_relocator_alloc_chunk_align (grub_multiboot2_relocator, &ch,
-                                         0, 0xffffffff - bufsize,
+                                         MBI_MIN_ADDR, 0xffffffff - bufsize,
                                          bufsize, MULTIBOOT_TAG_ALIGN,
                                          GRUB_RELOCATOR_PREFERENCE_NONE, 1);
   if (err)

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