linux-kernel - Re: [PATCH] kprobes: prohibit probes in gate area

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Date:   Thu, 8 Sep 2022 07:32:17 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     "Christian A. Ehrhardt" <lk@...e.de>
Cc:     linux-kernel@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] kprobes: prohibit probes in gate area

On Wed,  7 Sep 2022 22:09:17 +0200
"Christian A. Ehrhardt" <lk@...e.de> wrote:

> The system call gate area counts as kernel text but trying
> to install a kprobe in this area fails with an Oops later on.
> To fix this explicitly disallow the gate area for kprobes.
> 
> Found by syzkaller with the following reproducer:
> perf_event_open$cgroup(&(0x7f00000001c0)={0x6, 0x80, 0x0, 0x0, 0x0, 0x0, 0x80ffff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_config_ext={0x0, 0xffffffffff600000}}, 0xffffffffffffffff, 0x0, 0xffffffffffffffff, 0x0)
> 
> Sample report:
> BUG: unable to handle page fault for address: fffffbfff3ac6000
> PGD 6dfcb067 P4D 6dfcb067 PUD 6df8f067 PMD 6de4d067 PTE 0
> Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 0 PID: 21978 Comm: syz-executor.2 Not tainted 6.0.0-rc3-00363-g7726d4c3e60b-dirty #6
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:__insn_get_emulate_prefix arch/x86/lib/insn.c:91 [inline]
> RIP: 0010:insn_get_emulate_prefix arch/x86/lib/insn.c:106 [inline]
> RIP: 0010:insn_get_prefixes.part.0+0xa8/0x1110 arch/x86/lib/insn.c:134
> Code: 49 be 00 00 00 00 00 fc ff df 48 8b 40 60 48 89 44 24 08 e9 81 00 00 00 e8 e5 4b 39 ff 4c 89 fa 4c 89 f9 48 c1 ea 03 83 e1 07 <42> 0f b6 14 32 38 ca 7f 08 84 d2 0f 85 06 10 00 00 48 89 d8 48 89
> RSP: 0018:ffffc900088bf860 EFLAGS: 00010246
> RAX: 0000000000040000 RBX: ffffffff9b9bebc0 RCX: 0000000000000000
> RDX: 1ffffffff3ac6000 RSI: ffffc90002d82000 RDI: ffffc900088bf9e8
> RBP: ffffffff9d630001 R08: 0000000000000000 R09: ffffc900088bf9e8
> R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
> R13: ffffffff9d630000 R14: dffffc0000000000 R15: ffffffff9d630000
> FS:  00007f63eef63640(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffbfff3ac6000 CR3: 0000000029d90005 CR4: 0000000000770ef0
> PKRU: 55555554
> Call Trace:
>  <TASK>
>  insn_get_prefixes arch/x86/lib/insn.c:131 [inline]
>  insn_get_opcode arch/x86/lib/insn.c:272 [inline]
>  insn_get_modrm+0x64a/0x7b0 arch/x86/lib/insn.c:343
>  insn_get_sib+0x29a/0x330 arch/x86/lib/insn.c:421
>  insn_get_displacement+0x350/0x6b0 arch/x86/lib/insn.c:464
>  insn_get_immediate arch/x86/lib/insn.c:632 [inline]
>  insn_get_length arch/x86/lib/insn.c:707 [inline]
>  insn_decode+0x43a/0x490 arch/x86/lib/insn.c:747
>  can_probe+0xfc/0x1d0 arch/x86/kernel/kprobes/core.c:282
>  arch_prepare_kprobe+0x79/0x1c0 arch/x86/kernel/kprobes/core.c:739
>  prepare_kprobe kernel/kprobes.c:1160 [inline]
>  register_kprobe kernel/kprobes.c:1641 [inline]
>  register_kprobe+0xb6e/0x1690 kernel/kprobes.c:1603
>  __register_trace_kprobe kernel/trace/trace_kprobe.c:509 [inline]
>  __register_trace_kprobe+0x26a/0x2d0 kernel/trace/trace_kprobe.c:477
>  create_local_trace_kprobe+0x1f7/0x350 kernel/trace/trace_kprobe.c:1833
>  perf_kprobe_init+0x18c/0x280 kernel/trace/trace_event_perf.c:271
>  perf_kprobe_event_init+0xf8/0x1c0 kernel/events/core.c:9888
>  perf_try_init_event+0x12d/0x570 kernel/events/core.c:11261
>  perf_init_event kernel/events/core.c:11325 [inline]
>  perf_event_alloc.part.0+0xf7f/0x36a0 kernel/events/core.c:11619
>  perf_event_alloc kernel/events/core.c:12059 [inline]
>  __do_sys_perf_event_open+0x4a8/0x2a00 kernel/events/core.c:12157
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f63ef7efaed
> Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f63eef63028 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
> RAX: ffffffffffffffda RBX: 00007f63ef90ff80 RCX: 00007f63ef7efaed
> RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 00000000200001c0
> RBP: 00007f63ef86019c R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000002 R14: 00007f63ef90ff80 R15: 00007f63eef43000
>  </TASK>
> Modules linked in:
> CR2: fffffbfff3ac6000
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__insn_get_emulate_prefix arch/x86/lib/insn.c:91 [inline]
> RIP: 0010:insn_get_emulate_prefix arch/x86/lib/insn.c:106 [inline]
> RIP: 0010:insn_get_prefixes.part.0+0xa8/0x1110 arch/x86/lib/insn.c:134
> Code: 49 be 00 00 00 00 00 fc ff df 48 8b 40 60 48 89 44 24 08 e9 81 00 00 00 e8 e5 4b 39 ff 4c 89 fa 4c 89 f9 48 c1 ea 03 83 e1 07 <42> 0f b6 14 32 38 ca 7f 08 84 d2 0f 85 06 10 00 00 48 89 d8 48 89
> RSP: 0018:ffffc900088bf860 EFLAGS: 00010246
> RAX: 0000000000040000 RBX: ffffffff9b9bebc0 RCX: 0000000000000000
> RDX: 1ffffffff3ac6000 RSI: ffffc90002d82000 RDI: ffffc900088bf9e8
> RBP: ffffffff9d630001 R08: 0000000000000000 R09: ffffc900088bf9e8
> R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
> R13: ffffffff9d630000 R14: dffffc0000000000 R15: ffffffff9d630000
> FS:  00007f63eef63640(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffbfff3ac6000 CR3: 0000000029d90005 CR4: 0000000000770ef0
> PKRU: 55555554
> ==================================================================
> 

Good catch! kprobes should not probe vsyscall area.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Cc: stable@...r.kernel.org

Thank you,



> cc: "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
> cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
> cc: "David S. Miller" <davem@...emloft.net>
> cc: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Christian A. Ehrhardt <lk@...e.de>
> ---
>  kernel/kprobes.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 08350e35aba2..ca9d834d0b84 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1562,6 +1562,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	/* Ensure it is not in reserved area nor out of text */
>  	if (!(core_kernel_text((unsigned long) p->addr) ||
>  	    is_module_text_address((unsigned long) p->addr)) ||
> +	    in_gate_area_no_mm((unsigned long) p->addr) ||
>  	    within_kprobe_blacklist((unsigned long) p->addr) ||
>  	    jump_label_text_reserved(p->addr, p->addr) ||
>  	    static_call_text_reserved(p->addr, p->addr) ||
> -- 
> 2.34.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>