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.

Cc: stable@vger.kernel.org
Fixes: 00963a2e75 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
Signed-off-by: Chuang Wang <nashuiliang@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20221224133146.780578-1-nashuiliang@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/trampoline.c

@@ -488,6 +488,10 @@ again:
 		/* reset fops->func and fops->trampoline for re-register */
 		tr->fops->func = NULL;
 		tr->fops->trampoline = 0;
+
+		/* reset im->image memory attr for arch_prepare_bpf_trampoline */
+		set_memory_nx((long)im->image, 1);
+		set_memory_rw((long)im->image, 1);
 		goto again;
 	}
 #endif