mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-05 15:49:42 -04:00
deb5940046
The check for 4-byte load from dst_port offset into bpf_sock is failing on
big-endian architecture - s390. The bpf access converter rewrites the
4-byte load to a 2-byte load from sock_common at skc_dport offset, as shown
below.
* s390 / llvm-objdump -S --no-show-raw-insn
00000000000002a0 <sk_dst_port__load_word>:
84: r1 = *(u32 *)(r1 + 48)
85: w0 = 1
86: if w1 == 51966 goto +1 <LBB5_2>
87: w0 = 0
00000000000002c0 <LBB5_2>:
88: exit
* s390 / bpftool prog dump xlated
_Bool sk_dst_port__load_word(struct bpf_sock * sk):
35: (69) r1 = *(u16 *)(r1 +12)
36: (bc) w1 = w1
37: (b4) w0 = 1
38: (16) if w1 == 0xcafe goto pc+1
39: (b4) w0 = 0
40: (95) exit
* x86_64 / llvm-objdump -S --no-show-raw-insn
00000000000002a0 <sk_dst_port__load_word>:
84: r1 = *(u32 *)(r1 + 48)
85: w0 = 1
86: if w1 == 65226 goto +1 <LBB5_2>
87: w0 = 0
00000000000002c0 <LBB5_2>:
88: exit
* x86_64 / bpftool prog dump xlated
_Bool sk_dst_port__load_word(struct bpf_sock * sk):
33: (69) r1 = *(u16 *)(r1 +12)
34: (b4) w0 = 1
35: (16) if w1 == 0xfeca goto pc+1
36: (b4) w0 = 0
37: (95) exit
This leads to surprises if we treat the destination register contents as a
32-bit value, ignoring the fact that in reality it contains a 16-bit value.
On little-endian the register contents reflect the bpf_sock struct
definition, where the lower 16-bits contain the port number:
struct bpf_sock {
...
__be16 dst_port; /* offset 48 */
__u16 :16;
...
};
However, on big-endian the register contents suggest that field the layout
of bpf_sock struct is as so:
struct bpf_sock {
...
__u16 :16; /* offset 48 */
__be16 dst_port;
...
};
Account for this quirky access conversion in the test case exercising the
4-byte load by treating the result as 16-bit wide.
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220317113920.1068535-5-jakub@cloudflare.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.