On 24 Jan 09:20, Kees Cook wrote:
In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.
Use flexible arrays instead of zero-element arrays (which look like they
are always overflowing) and split the cross-field memcpy() into two halves
that can be appropriately bounds-checked by the compiler.
We were doing:
#define ETH_HLEN 14
#define VLAN_HLEN 4
...
#define MLX5E_XDP_MIN_INLINE (ETH_HLEN + VLAN_HLEN)
...
struct mlx5e_tx_wqe *wqe = mlx5_wq_cyc_get_wqe(wq, pi);
...
struct mlx5_wqe_eth_seg *eseg = &wqe->eth;
struct mlx5_wqe_data_seg *dseg = wqe->data;
...
memcpy(eseg->inline_hdr.start, xdptxd->data, MLX5E_XDP_MIN_INLINE);
target is wqe->eth.inline_hdr.start (which the compiler sees as being
2 bytes in size), but copying 18, intending to write across start
(really vlan_tci, 2 bytes). The remaining 16 bytes get written into
wqe->data[0], covering byte_count (4 bytes), lkey (4 bytes), and addr
(8 bytes).
struct mlx5e_tx_wqe {
struct mlx5_wqe_ctrl_seg ctrl; /* 0 16 */
struct mlx5_wqe_eth_seg eth; /* 16 16 */
struct mlx5_wqe_data_seg data[]; /* 32 0 */
/* size: 32, cachelines: 1, members: 3 */
/* last cacheline: 32 bytes */
};
struct mlx5_wqe_eth_seg {
u8 swp_outer_l4_offset; /* 0 1 */
u8 swp_outer_l3_offset; /* 1 1 */
u8 swp_inner_l4_offset; /* 2 1 */
u8 swp_inner_l3_offset; /* 3 1 */
u8 cs_flags; /* 4 1 */
u8 swp_flags; /* 5 1 */
__be16 mss; /* 6 2 */
__be32 flow_table_metadata; /* 8 4 */
union {
struct {
__be16 sz; /* 12 2 */
u8 start[2]; /* 14 2 */
} inline_hdr; /* 12 4 */
struct {
__be16 type; /* 12 2 */
__be16 vlan_tci; /* 14 2 */
} insert; /* 12 4 */
__be32 trailer; /* 12 4 */
}; /* 12 4 */
/* size: 16, cachelines: 1, members: 9 */
/* last cacheline: 16 bytes */
};
struct mlx5_wqe_data_seg {
__be32 byte_count; /* 0 4 */
__be32 lkey; /* 4 4 */
__be64 addr; /* 8 8 */
/* size: 16, cachelines: 1, members: 3 */
/* last cacheline: 16 bytes */
};
So, split the memcpy() so the compiler can reason about the buffer
sizes.
"pahole" shows no size nor member offset changes to struct mlx5e_tx_wqe
nor struct mlx5e_umr_wqe. "objdump -d" shows no meaningful object
code changes (i.e. only source line number induced differences and
optimizations).
Cc: Saeed Mahameed <saeedm@xxxxxxxxxx>
Cc: Leon Romanovsky <leon@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Cc: linux-rdma@xxxxxxxxxxxxxxx
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Since this results in no binary differences, I will carry this in my tree
unless someone else wants to pick it up. It's one of the last remaining
clean-ups needed for the next step in memcpy() hardening.
applied to net-next-mlx5.
Thanks,
Saeed
