On 18/02/2023 20:38, Kees Cook wrote:
The call "skb_copy_from_linear_data(skb, inl + 1, spc)" triggers a FORTIFY
memcpy() warning on ppc64 platform:
In function ‘fortify_memcpy_chk’,
inlined from ‘skb_copy_from_linear_data’ at ./include/linux/skbuff.h:4029:2,
inlined from ‘build_inline_wqe’ at drivers/net/ethernet/mellanox/mlx4/en_tx.c:722:4,
inlined from ‘mlx4_en_xmit’ at drivers/net/ethernet/mellanox/mlx4/en_tx.c:1066:3:
./include/linux/fortify-string.h:513:25: error: call to ‘__write_overflow_field’ declared with
attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()?
[-Werror=attribute-warning]
513 | __write_overflow_field(p_size_field, size);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Same behaviour on x86 you can get if you use "__always_inline" instead of
"inline" for skb_copy_from_linear_data() in skbuff.h
The call here copies data into inlined tx destricptor, which has 104
bytes (MAX_INLINE) space for data payload. In this case "spc" is known
in compile-time but the destination is used with hidden knowledge
(real structure of destination is different from that the compiler
can see). That cause the fortify warning because compiler can check
bounds, but the real bounds are different. "spc" can't be bigger than
64 bytes (MLX4_INLINE_ALIGN), so the data can always fit into inlined
tx descriptor. The fact that "inl" points into inlined tx descriptor is
determined earlier in mlx4_en_xmit().
Avoid confusing the compiler with "inl + 1" constructions to get to past
the inl header by introducing a flexible array "data" to the struct so
that the compiler can see that we are not dealing with an array of inl
structs, but rather, arbitrary data following the structure. There are
no changes to the structure layout reported by pahole, and the resulting
machine code is actually smaller.
Reported-by: Josef Oskera <joskera@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230217094541.2362873-1-joskera@xxxxxxxxxx
Fixes: f68f2ff91512 ("fortify: Detect struct member overflows in memcpy() at compile-time")
Cc: Tariq Toukan <tariqt@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: Yishai Hadas <yishaih@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Cc: linux-rdma@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
drivers/net/ethernet/mellanox/mlx4/en_tx.c | 22 +++++++++++-----------
include/linux/mlx4/qp.h | 1 +
2 files changed, 12 insertions(+), 11 deletions(-)
Just saw your patch now, after commenting on the other thread. :)
So you choose not to fix similar usages in RDMA driver
drivers/infiniband/hw/mlx4/qp.c, like:
3204 spc = MLX4_INLINE_ALIGN -
3205 ((unsigned long) (inl + 1) & (MLX4_INLINE_ALIGN - 1));
3206 if (header_size <= spc) {
3207 inl->byte_count = cpu_to_be32(1 << 31 | header_size);
3208 memcpy(inl + 1, sqp->header_buf, header_size);
3209 i = 1;
3210 } else {
3211 inl->byte_count = cpu_to_be32(1 << 31 | spc);
3212 memcpy(inl + 1, sqp->header_buf, spc);
3213
3214 inl = (void *) (inl + 1) + spc;
3215 memcpy(inl + 1, sqp->header_buf + spc, header_size
- spc);
This keeps the patch minimal indeed.
Did you repro the issue and test this solution?
Maybe Josef can also verify it works for him?
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index c5758637b7be..2f79378fbf6e 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -699,32 +699,32 @@ static void build_inline_wqe(struct mlx4_en_tx_desc *tx_desc,
inl->byte_count = cpu_to_be32(1 << 31 | skb->len);
} else {
inl->byte_count = cpu_to_be32(1 << 31 | MIN_PKT_LEN);
- memset(((void *)(inl + 1)) + skb->len, 0,
+ memset(inl->data + skb->len, 0,
MIN_PKT_LEN - skb->len);
}
- skb_copy_from_linear_data(skb, inl + 1, hlen);
+ skb_copy_from_linear_data(skb, inl->data, hlen);
if (shinfo->nr_frags)
- memcpy(((void *)(inl + 1)) + hlen, fragptr,
+ memcpy(inl->data + hlen, fragptr,
skb_frag_size(&shinfo->frags[0]));
} else {
inl->byte_count = cpu_to_be32(1 << 31 | spc);
if (hlen <= spc) {
- skb_copy_from_linear_data(skb, inl + 1, hlen);
+ skb_copy_from_linear_data(skb, inl->data, hlen);
if (hlen < spc) {
- memcpy(((void *)(inl + 1)) + hlen,
+ memcpy(inl->data + hlen,
fragptr, spc - hlen);
fragptr += spc - hlen;
}
- inl = (void *) (inl + 1) + spc;
- memcpy(((void *)(inl + 1)), fragptr, skb->len - spc);
+ inl = (void *)inl->data + spc;
+ memcpy(inl->data, fragptr, skb->len - spc);
} else {
- skb_copy_from_linear_data(skb, inl + 1, spc);
- inl = (void *) (inl + 1) + spc;
- skb_copy_from_linear_data_offset(skb, spc, inl + 1,
+ skb_copy_from_linear_data(skb, inl->data, spc);
+ inl = (void *)inl->data + spc;
No need now for all these (void *) castings.
+ skb_copy_from_linear_data_offset(skb, spc, inl->data,
hlen - spc);
if (shinfo->nr_frags)
- memcpy(((void *)(inl + 1)) + hlen - spc,
+ memcpy(inl->data + hlen - spc,
fragptr,
skb_frag_size(&shinfo->frags[0]));
}
diff --git a/include/linux/mlx4/qp.h b/include/linux/mlx4/qp.h
index c78b90f2e9a1..b9a7b1319f5d 100644
--- a/include/linux/mlx4/qp.h
+++ b/include/linux/mlx4/qp.h
@@ -446,6 +446,7 @@ enum {
struct mlx4_wqe_inline_seg {
__be32 byte_count;
+ __u8 data[];
};
enum mlx4_update_qp_attr {
