From: Chuang Wang nashuiliang@gmail.com
commit 9ed1d9aeef5842ecacb660fce933613b58af1e00 upstream.
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: 00963a2e75a8 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/trampoline.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -501,6 +501,10 @@ 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