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xsk: fix u64 descriptor address truncation on 32-bit architectures

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In copy mode TX, xsk_skb_destructor_set_addr() stores the 64-bit
descriptor address into skb_shinfo(skb)->destructor_arg (void *) via a
uintptr_t cast:

    skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t)addr | 0x1UL);

On 32-bit architectures uintptr_t is 32 bits, so the upper 32 bits of
the descriptor address are silently dropped. In XDP_ZEROCOPY unaligned
mode the chunk offset is encoded in bits 48-63 of the descriptor
address (XSK_UNALIGNED_BUF_OFFSET_SHIFT = 48), meaning the offset is
lost entirely. The completion queue then returns a truncated address to
userspace, making buffer recycling impossible.

Fix this by handling the 32-bit case directly in
xsk_skb_destructor_set_addr(): when !CONFIG_64BIT, allocate an
xsk_addrs struct (the same path already used for multi-descriptor
SKBs) to store the full u64 address. The existing tagged-pointer logic
in xsk_skb_destructor_is_addr() stays unchanged: slab pointers returned
from kmem_cache_zalloc() are always word-aligned and therefore have
bit 0 clear, which correctly identifies them as a struct pointer
rather than an inline tagged address on every architecture.

Factor the shared kmem_cache_zalloc + destructor_arg assignment into
__xsk_addrs_alloc() and add a wrapper xsk_addrs_alloc() that handles
the inline-to-list upgrade (is_addr check + get_addr + num_descs = 1).
The three former open-coded kmem_cache_zalloc call sites now reduce to
a single call each.

Propagate the -ENOMEM from xsk_skb_destructor_set_addr() through
xsk_skb_init_misc() so the caller can clean up the skb via kfree_skb()
before skb->destructor is installed.

The overhead is one extra kmem_cache_zalloc per first descriptor on
32-bit only; 64-bit builds are completely unchanged.

Closes: https://lore.kernel.org/all/20260419045824.D9E5EC2BCAF@smtp.kernel.org/
Fixes: 0ebc27a4c6 ("xsk: avoid data corruption on cq descriptor number")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://patch.msgid.link/20260502200722.53960-9-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jason Xing
2026-05-02 23:07:22 +03:00
committed by Jakub Kicinski
parent e0f229025a
commit 203cee647f
1 changed files with 56 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

88
net/xdp/xsk.c
View File

@@ -646,9 +646,42 @@ static u64 xsk_skb_destructor_get_addr(struct sk_buff *skb)
return (u64)((uintptr_t)skb_shinfo(skb)->destructor_arg & ~0x1UL);
}
static void xsk_skb_destructor_set_addr(struct sk_buff *skb, u64 addr)
static struct xsk_addrs *__xsk_addrs_alloc(struct sk_buff *skb, u64 addr)
{
skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t)addr | 0x1UL);
struct xsk_addrs *xsk_addr;
xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache, GFP_KERNEL);
if (unlikely(!xsk_addr))
return NULL;
xsk_addr->addrs[0] = addr;
skb_shinfo(skb)->destructor_arg = (void *)xsk_addr;
return xsk_addr;
}
static struct xsk_addrs *xsk_addrs_alloc(struct sk_buff *skb)
{
struct xsk_addrs *xsk_addr;
if (!xsk_skb_destructor_is_addr(skb))
return (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg;
xsk_addr = __xsk_addrs_alloc(skb, xsk_skb_destructor_get_addr(skb));
if (likely(xsk_addr))
xsk_addr->num_descs = 1;
return xsk_addr;
}
static int xsk_skb_destructor_set_addr(struct sk_buff *skb, u64 addr)
{
if (IS_ENABLED(CONFIG_64BIT)) {
skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t)addr | 0x1UL);
return 0;
}
if (unlikely(!__xsk_addrs_alloc(skb, addr)))
return -ENOMEM;
return 0;
}
static void xsk_inc_num_desc(struct sk_buff *skb)
@@ -724,14 +757,20 @@ void xsk_destruct_skb(struct sk_buff *skb)
sock_wfree(skb);
}
static void xsk_skb_init_misc(struct sk_buff *skb, struct xdp_sock *xs,
u64 addr)
static int xsk_skb_init_misc(struct sk_buff *skb, struct xdp_sock *xs,
u64 addr)
{
int err;
err = xsk_skb_destructor_set_addr(skb, addr);
if (unlikely(err))
return err;
skb->dev = xs->dev;
skb->priority = READ_ONCE(xs->sk.sk_priority);
skb->mark = READ_ONCE(xs->sk.sk_mark);
skb->destructor = xsk_destruct_skb;
xsk_skb_destructor_set_addr(skb, addr);
return 0;
}
static void xsk_consume_skb(struct sk_buff *skb)
@@ -829,18 +868,9 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
} else {
struct xsk_addrs *xsk_addr;
if (xsk_skb_destructor_is_addr(skb)) {
xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache,
GFP_KERNEL);
if (!xsk_addr)
return ERR_PTR(-ENOMEM);
xsk_addr->num_descs = 1;
xsk_addr->addrs[0] = xsk_skb_destructor_get_addr(skb);
skb_shinfo(skb)->destructor_arg = (void *)xsk_addr;
} else {
xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg;
}
xsk_addr = xsk_addrs_alloc(skb);
if (!xsk_addr)
return ERR_PTR(-ENOMEM);
/* in case of -EOVERFLOW that could happen below,
* xsk_consume_skb() will release this node as whole skb
@@ -929,19 +959,10 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
struct page *page;
u8 *vaddr;
if (xsk_skb_destructor_is_addr(skb)) {
xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache,
GFP_KERNEL);
if (!xsk_addr) {
err = -ENOMEM;
goto free_err;
}
xsk_addr->num_descs = 1;
xsk_addr->addrs[0] = xsk_skb_destructor_get_addr(skb);
skb_shinfo(skb)->destructor_arg = (void *)xsk_addr;
} else {
xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg;
xsk_addr = xsk_addrs_alloc(skb);
if (!xsk_addr) {
err = -ENOMEM;
goto free_err;
}
if (unlikely(nr_frags == (MAX_SKB_FRAGS - 1) && xp_mb_desc(desc))) {
@@ -966,8 +987,11 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
}
}
if (!xs->skb)
xsk_skb_init_misc(skb, xs, desc->addr);
if (!xs->skb) {
err = xsk_skb_init_misc(skb, xs, desc->addr);
if (unlikely(err))
goto free_err;
}
xsk_inc_num_desc(skb);
return skb;