[3.16.y-ckt stable] Patch "efi/libstub: Fix boundary checking in efi_high_alloc()" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Thu Mar 19 10:12:38 UTC 2015

This is a note to let you know that I have just added a patch titled

    efi/libstub: Fix boundary checking in efi_high_alloc()

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see



>From 28e78736f72abaeeb40ae1831e430552f35c0f69 Mon Sep 17 00:00:00 2001
From: Yinghai Lu <yinghai at kernel.org>
Date: Thu, 19 Feb 2015 20:18:03 -0800
Subject: efi/libstub: Fix boundary checking in efi_high_alloc()

commit 7ed620bb343f434f8a85f830020c04988df2a140 upstream.

While adding support loading kernel and initrd above 4G to grub2 in legacy
mode, I was referring to efi_high_alloc().
That will allocate buffer for kernel and then initrd, and initrd will
use kernel buffer start as limit.

During testing found two buffers will be overlapped when initrd size is
very big like 400M.

It turns out efi_high_alloc() boundary checking is not right.
end - size will be the new start, and should not compare new
start with max, we need to make sure end is smaller than max.

[ Basically, with the current efi_high_alloc() code it's possible to
  allocate memory above 'max', because efi_high_alloc() doesn't check
  that the tail of the allocation is below 'max'.

  If you have an EFI memory map with a single entry that looks like so,


  And want to allocate 0x3000 bytes below 0xc0003000 the current code
  will allocate [0xc0001000-0xc0004000], not [0xc0000000-0xc0003000]
  like you would expect. - Matt ]

Signed-off-by: Yinghai Lu <yinghai at kernel.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Reviewed-by: Mark Rutland <mark.rutland at arm.com>
Tested-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Matt Fleming <matt.fleming at intel.com>
[ luis: backported to 3.16:
  - file rename: drivers/firmware/efi/libstub/efi-stub-helper.c ->
    drivers/firmware/efi/efi-stub-helper.c ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/firmware/efi/efi-stub-helper.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/efi-stub-helper.c b/drivers/firmware/efi/efi-stub-helper.c
index eb6d4be9e722..2fb3a0aab56c 100644
--- a/drivers/firmware/efi/efi-stub-helper.c
+++ b/drivers/firmware/efi/efi-stub-helper.c
@@ -157,12 +157,12 @@ again:
 		start = desc->phys_addr;
 		end = start + desc->num_pages * (1UL << EFI_PAGE_SHIFT);

-		if ((start + size) > end || (start + size) > max)
-			continue;
-		if (end - size > max)
+		if (end > max)
 			end = max;

+		if ((start + size) > end)
+			continue;
 		if (round_down(end - size, align) < start)

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