From: Vitaly Kuznetsov <vkuzn...@redhat.com>

Commit 78ce248faa3c ("efi: Iterate over efi.memmap in
for_each_efi_memory_desc()") introduced a regression for systems booted
with 'noefi' kernel option. In particular, I observe early kernel hang in
efi_find_mirror() on for_each_efi_memory_desc() call. As we don't have
efi memmap we enter this iterator with the following parameters:

efi.memmap.map = 0, efi.memmap.map_end = 0, efi.memmap.desc_size = 28

for_each_efi_memory_desc_in_map() does the following comparison:

(md) <= (efi_memory_desc_t *)((m)->map_end - (m)->desc_size);

where md = 0, (m)->map_end = 0 and (m)->desc_size = 28 but when we subtract
something from a NULL pointer wrap around happens and we end up returning
invalid pointer.

Fixes: 78ce248faa3c ("efi: Iterate over efi.memmap in 
for_each_efi_memory_desc()")
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
Cc: Mark Salter <msal...@redhat.com>
Cc: "K. Y. Srinivasan" <k...@microsoft.com>
Signed-off-by: Matt Fleming <m...@codeblueprint.co.uk>
---
 include/linux/efi.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/efi.h b/include/linux/efi.h
index c2db3ca22217..f196dd0b0f2f 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1005,7 +1005,7 @@ extern int efi_memattr_apply_permissions(struct mm_struct 
*mm,
 /* Iterate through an efi_memory_map */
 #define for_each_efi_memory_desc_in_map(m, md)                            \
        for ((md) = (m)->map;                                              \
-            (md) <= (efi_memory_desc_t *)((m)->map_end - (m)->desc_size); \
+            ((void *)(md) + (m)->desc_size) <= (m)->map_end;              \
             (md) = (void *)(md) + (m)->desc_size)
 
 /**
-- 
2.7.3

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