[PATCH] efi/libstub: Fix boundary checking in efi_high_alloc()

From: Yinghai Lu
Date: Thu Feb 19 2015 - 23:18:03 EST

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@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Matt Fleming <matt.fleming@xxxxxxxxx>
drivers/firmware/efi/libstub/efi-stub-helper.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 9bd9fbb5bea8..c927bccd92bd 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -170,12 +170,12 @@ 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)


Matt Fleming, Intel Open Source Technology Center
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/