[PATCH] x86/alternatives: add missing mutex lock in,alternatives_text_reserved

[Rui Xiang <rui.xiang@huawei.com>]

A race between alternatives_text_reserved and alternatives_smp_module_del
occured when traversing the global list smp_alt_modules in 3.4 kernel. It
would casue a panic while reading smp_alt_modules->mod in
alternatives_text_reserved func.

[   14.016190] general protection fault: 0000 [#1] SMP
[   14.016988] CPU 0
[   14.017287] Modules linked in: mlx4_ib(O+) mlx4_en(O+) xb_sa(O)
[   14.020005]
[   14.020005] Pid: 1979, comm: modprobe Tainted: G           O
[   14.020005] RIP: 0010:[<ffffffff81007eb0>]  [<ffffffff81007eb0>] alternatives_text_reserved+0x20/0x80
[   14.020005] RSP: 0018:ffff880ea355bcb8  EFLAGS: 00010283
[   14.020005] RAX: dead000000000100 RBX: ffffffffa02af720 RCX: dead0000000000d0
[   14.020005] RDX: ffffffffa02f0588 RSI: ffffffffa02d2fc0 RDI: ffffffffa02d2fc0
[   14.020005] RBP: ffff880ea355bcb8 R08: ffffffffa02f3b68 R09: 00017f4ae12d2fc0
[   14.020005] R10: 00000000000000e8 R11: ffffffffa02bb9d7 R12: 0000000000000000
[   14.020005] R13: ffffffffa02af720 R14: ffffffffa0307140 R15: ffffffffa02af730
[   14.020005] FS:  00007f26c6acc700(0000) GS:ffff880fff200000(0000) knlGS:0000000000000000
[   14.020005] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[   14.020005] CR2: 00007fd4adc3b000 CR3: 0000000ea40ea000 CR4: 00000000001407f0
[   14.020005] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   14.020005] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   14.020005] Process modprobe (pid: 1979, threadinfo ffff880ea355a000, task ffff880e9eb9e600)
[   14.020005] Stack:
[   14.020005]  ffff880ea355bcd8 ffffffff8145b148 ffffffffa02af720 ffffffffa02af720
[   14.020005]  ffff880ea355bd18 ffffffff8145ed38 0000000000000000 0000000000000000
[   14.041015]  ffff880ea355bd90 ffffffffa02af720 0000000000000001 ffff880ea355bd90
[   14.041015] Call Trace:
[   14.041015]  [<ffffffff8145b148>] arch_prepare_kprobe+0x18/0x80
[   14.042982]  [<ffffffff8145ed38>] register_kprobe+0x338/0x4c0
[   14.042982]  [<ffffffff8145f658>] register_jprobes+0x98/0xc0
[   14.042982]  [<ffffffff8145f69a>] register_jprobe+0x1a/0x20

It also seems to exist in mainline.

This patch adds the mutex lock smp_alt to fix it.

Cc: stable@vger.kernel.org
Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
---
 arch/x86/kernel/alternative.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 5cb272a..7cec0cc 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -563,6 +563,7 @@ int alternatives_text_reserved(void *start, void *end)
 	u8 *text_start = start;
 	u8 *text_end = end;

+	mutex_lock(&smp_alt);
 	list_for_each_entry(mod, &smp_alt_modules, next) {
 		if (mod->text > text_end || mod->text_end < text_start)
 			continue;
@@ -573,6 +574,7 @@ int alternatives_text_reserved(void *start, void *end)
 				return 1;
 		}
 	}
+	mutex_unlock(&smp_alt);	

 	return 0;
 }
-- 
1.8.2.2