bpf: Fix panic due to wrong pageattr of im->image

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix panic due to wrong pageattr of im->image

In the scenario where livepatch and kretfunc coexist, the pageattr of

im->image is rox after arch_prepare_bpf_trampoline in

bpf_trampoline_update, and then modify_fentry or register_fentry returns

-EAGAIN from bpf_tramp_ftrace_ops_func, the BPF_TRAMP_F_ORIG_STACK flag

will be configured, and arch_prepare_bpf_trampoline will be re-executed.

At this time, because the pageattr of im->image is rox,

arch_prepare_bpf_trampoline will read and write im->image, which causes

a fault. as follows:

insmod livepatch-sample.ko # samples/livepatch/livepatch-sample.c

bpftrace -e 'kretfunc:cmdline_proc_show {}'

BUG: unable to handle page fault for address: ffffffffa0206000

PGD 322d067 P4D 322d067 PUD 322e063 PMD 1297e067 PTE d428061

Oops: 0003 [#1] PREEMPT SMP PTI

CPU: 2 PID: 270 Comm: bpftrace Tainted: G E K 6.1.0 #5

RIP: 0010:arch_prepare_bpf_trampoline+0xed/0x8c0

RSP: 0018:ffffc90001083ad8 EFLAGS: 00010202

RAX: ffffffffa0206000 RBX: 0000000000000020 RCX: 0000000000000000

RDX: ffffffffa0206001 RSI: ffffffffa0206000 RDI: 0000000000000030

RBP: ffffc90001083b70 R08: 0000000000000066 R09: ffff88800f51b400

R10: 000000002e72c6e5 R11: 00000000d0a15080 R12: ffff8880110a68c8

R13: 0000000000000000 R14: ffff88800f51b400 R15: ffffffff814fec10

FS: 00007f87bc0dc780(0000) GS:ffff88803e600000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffa0206000 CR3: 0000000010b70000 CR4: 00000000000006e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

<TASK>

bpf_trampoline_update+0x25a/0x6b0

__bpf_trampoline_link_prog+0x101/0x240

bpf_trampoline_link_prog+0x2d/0x50

bpf_tracing_prog_attach+0x24c/0x530

bpf_raw_tp_link_attach+0x73/0x1d0

__sys_bpf+0x100e/0x2570

__x64_sys_bpf+0x1c/0x30

do_syscall_64+0x5b/0x80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

With this patch, when modify_fentry or register_fentry returns -EAGAIN

from bpf_tramp_ftrace_ops_func, the pageattr of im->image will be reset

to nx+rw.