[PATCH 4.16 176/279] IB/mlx4: Fix integer overflow when calculating optimal MTT size

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jack Morgenstein <jackm@xxxxxxxxxxxxxxxxxx>

[ Upstream commit b03bcde962606d2ee59a4e9dd470db9ad53c5418 ]

When the kernel was compiled using the UBSAN option,
we saw the following stack trace:

[ 1184.827917] UBSAN: Undefined behaviour in drivers/infiniband/hw/mlx4/mr.c:349:27
[ 1184.828114] signed integer overflow:
[ 1184.828247] -2147483648 - 1 cannot be represented in type 'int'

The problem was caused by calling round_up in procedure
mlx4_ib_umem_calc_optimal_mtt_size (on line 349, as noted in the stack
trace) with the second parameter (1 << block_shift) (which is an int).
The second parameter should have been (1ULL << block_shift) (which
is an unsigned long long).

(1 << block_shift) is treated by the compiler as an int (because 1 is
an integer).

Now, local variable block_shift is initialized to 31.
If block_shift is 31, 1 << block_shift is 1 << 31 = 0x80000000=-214748368.
This is the most negative int value.

Inside the round_up macro, there is a cast applied to ((1 << 31) - 1).
However, this cast is applied AFTER ((1 << 31) - 1) is calculated.
Since (1 << 31) is treated as an int, we get the negative overflow
identified by UBSAN in the process of calculating ((1 << 31) - 1).

The fix is to change (1 << block_shift) to (1ULL << block_shift) on
line 349.

Fixes: 9901abf58368 ("IB/mlx4: Use optimal numbers of MTT entries")
Signed-off-by: Jack Morgenstein <jackm@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
Signed-off-by: Doug Ledford <dledford@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/infiniband/hw/mlx4/mr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/infiniband/hw/mlx4/mr.c
+++ b/drivers/infiniband/hw/mlx4/mr.c
@@ -346,7 +346,7 @@ int mlx4_ib_umem_calc_optimal_mtt_size(s
 	/* Add to the first block the misalignment that it suffers from. */
 	total_len += (first_block_start & ((1ULL << block_shift) - 1ULL));
 	last_block_end = current_block_start + current_block_len;
-	last_block_aligned_end = round_up(last_block_end, 1 << block_shift);
+	last_block_aligned_end = round_up(last_block_end, 1ULL << block_shift);
 	total_len += (last_block_aligned_end - last_block_end);
 
 	if (total_len & ((1ULL << block_shift) - 1ULL))