linux-kernel - [PATCH 1/2] efi: Fix for_each_efi_memory_desc_in

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Message-Id: <1464690224-4503-2-git-send-email-matt@codeblueprint.co.uk>
Date:	Tue, 31 May 2016 11:23:43 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>
Cc:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	Matt Fleming <matt@...eblueprint.co.uk>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Mark Salter <msalter@...hat.com>
Subject: [PATCH 1/2] efi: Fix for_each_efi_memory_desc_in_map() for empty memmaps

From: Vitaly Kuznetsov <vkuznets@...hat.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 <vkuznets@...hat.com>
Cc: Mark Salter <msalter@...hat.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Signed-off-by: Matt Fleming <matt@...eblueprint.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