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Date: Thu, 14 Feb 2019 08:05:24 +0800
From: Changbin Du <changbin.du@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Changbin Du <changbin.du@...il.com>, mingo@...hat.com,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] kprobe: safely access memory specified by userspace
On Wed, Feb 13, 2019 at 10:41:43AM -0500, Steven Rostedt wrote:
> On Wed, 13 Feb 2019 22:36:40 +0800
> Changbin Du <changbin.du@...il.com> wrote:
>
> > Hi Steven,
> > I think this is a critical issue. Could you give priority to this fix?
> >
> > On Fri, Jan 25, 2019 at 11:10:50PM +0800, Changbin Du wrote:
> > > The userspace can ask kprobe to intercept strings at any memory address,
> > > including invalid kernel address. In this case, fetch_store_strlen()
> > > would crash since it uses general usercopy function.
> > >
> > > For example, we can crash the kernel by doing something as below:
> > >
> > > $ sudo kprobe 'p:do_sys_open +0(+0(%si)):string'
>
> Note, I'm not able to reproduce this.
>
> I just get:
>
> sendmail-1085 [001] .... 277.344573: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.879011: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.879056: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.879079: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.879132: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.879683: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.881521: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1550 [003] .... 279.881541: open: (do_sys_open+0x0/0x210) arg1=""
> <...>-1597 [005] .... 280.907662: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1597 [005] .... 280.907694: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1597 [005] .... 280.907772: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1597 [005] .... 280.907825: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1597 [005] .... 280.907891: open: (do_sys_open+0x0/0x210) arg1=(fault)
> <...>-1597 [005] .... 280.907947: open: (do_sys_open+0x0/0x210) arg1=(fault)
>
>
> > >
> > > [ 103.620391] BUG: GPF in non-whitelisted uaccess (non-canonical address?)
> > > [ 103.622104] general protection fault: 0000 [#1] SMP PTI
> > > [ 103.623424] CPU: 10 PID: 1046 Comm: cat Not tainted 5.0.0-rc3-00130-gd73aba1-dirty #96
> > > [ 103.625321] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-2-g628b2e6-dirty-20190104_103505-linux 04/01/2014
> > > [ 103.628284] RIP: 0010:process_fetch_insn+0x1ab/0x4b0
>
> What line number is the RIP on?
>
I still can reproduce this bug on mainline (1f947a7a011fcceb14cb912f5481a53b18f1879a).
But it seems your linux has already fix this issue.
Panic msg:
i440FX-PIIX login: [ 265.640531] BUG: GPF in non-whitelisted uaccess (non-canonical address?)
[ 265.644365] general protection fault: 0000 [#1] SMP PTI
[ 265.645227] CPU: 0 PID: 2044 Comm: cat Not tainted 5.0.0-rc6+ #25
[ 265.646251] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-4-g29ba89e 04/01/2014
[ 265.647754] RIP: 0010:process_fetch_insn+0x1a3/0x450
[ 265.648498] Code: ff f0 80 48 03 80 83 80 88 21 00 00 01 31 c9 eb 10 48 83 c2 01 85 c0 75 1f 81 f9 ff 0f 00 00 7f 17 0f 01 cb 0f ae e8 44 89 e0 <40> 8a 32 0f 01 ca 83 c1 01 40 84 f6 75 d9 65 48 8b 14 25 40 5c 01
[ 265.651117] RSP: 0018:ffffc90001b1fd00 EFLAGS: 00050246
[ 265.651862] RAX: 0000000000000000 RBX: ffff88812d4a9100 RCX: 0000000000000000
[ 265.652917] RDX: 2e646c2f6374652f RSI: 00007ff31f818430 RDI: 00007ffffffff000
[ 265.653918] RBP: 0000000000000000 R08: 2e646c2f6374652f R09: 0000000000000000
[ 265.654881] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 265.655815] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[ 265.656746] FS: 0000000000000000(0000) GS:ffff88807d600000(0000) knlGS:0000000000000000
[ 265.657838] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 265.658680] CR2: 00007fff979b8038 CR3: 000000002e7b0005 CR4: 00000000003606f0
[ 265.659748] Call Trace:
[ 265.660225] kprobe_trace_func+0x278/0x360
[ 265.661119] ? trace_hardirqs_on+0x2c/0xd0
[ 265.661824] ? kmem_cache_free+0x1a7/0x1d0
[ 265.662366] ? do_sys_open+0x5/0x220
[ 265.662858] kprobe_dispatcher+0x36/0x50
[ 265.663362] ? do_sys_open+0x1/0x220
[ 265.663832] kprobe_ftrace_handler+0x92/0xf0
[ 265.664376] ftrace_ops_assist_func+0x81/0xf0
[ 265.664957] ? __call_rcu.constprop.49+0xca/0x210
[ 265.665583] 0xffffffffc00040bf
[ 265.665990] ? __ia32_sys_open+0x20/0x20
[ 265.666502] ? do_sys_open+0x1/0x220
[ 265.667041] do_sys_open+0x5/0x220
[ 265.667483] do_syscall_64+0x60/0xf0
[ 265.667971] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 265.668613] RIP: 0033:0x7ff31f813cdd
[ 265.669088] Code: 48 89 54 24 e0 41 83 e2 40 75 32 89 f0 25 00 00 41 00 3d 00 00 41 00 74 24 89 f2 b8 01 01 00 00 48 89 fe bf 9c ff ff ff 0f 05 <48> 3d 00 f0 ff ff 77 33 f3 c3 66 0f 1f 84 00 00 00 00 00 48 8d 44
[ 265.671330] RSP: 002b:00007fff978d8448 EFLAGS: 00000287 ORIG_RAX: 0000000000000101
[ 265.672206] RAX: ffffffffffffffda RBX: 000056396c8afa21 RCX: 00007ff31f813cdd
[ 265.673065] RDX: 0000000000080000 RSI: 00007ff31f818428 RDI: 00000000ffffff9c
[ 265.673887] RBP: ffffffffffffffff R08: 0000000000000000 R09: 0000000000000000
[ 265.674680] R10: 0000000000000000 R11: 0000000000000287 R12: 00007ff31fa200a8
[ 265.675465] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
[ 265.676258] Modules linked in:
[ 265.676972] ---[ end trace b0d3ddba0b051f18 ]---
The location is:
changbin@...top:/home/work/linux$ scripts/faddr2line --list vmlinux process_fetch_insn+0x1a3
process_fetch_insn+0x1a3/0x450:
raw_copy_from_user at arch/x86/include/asm/uaccess_64.h:75
70 if (!__builtin_constant_p(size))
71 return copy_user_generic(dst, (__force void *)src, size);
72 switch (size) {
73 case 1:
74 __uaccess_begin_nospec();
>75< __get_user_asm_nozero(*(u8 *)dst, (u8 __user *)src,
76 ret, "b", "b", "=q", 1);
77 __uaccess_end();
78 return ret;
79 case 2:
80 __uaccess_begin_nospec();
(inlined by) __copy_from_user_inatomic at include/linux/uaccess.h:63
58 static __always_inline unsigned long
59 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
60 {
61 kasan_check_write(to, n);
62 check_object_size(to, n, false);
>63< return raw_copy_from_user(to, from, n);
64 }
65
66 static __always_inline unsigned long
67 __copy_from_user(void *to, const void __user *from, unsigned long n)
68 {
(inlined by) fetch_store_strlen at kernel/trace/trace_kprobe.c:873
868 old_fs = get_fs();
869 set_fs(KERNEL_DS);
870 pagefault_disable();
871
872 do {
>873< ret = __copy_from_user_inatomic(&c, (u8 *)addr + len, 1);
874 len++;
875 } while (c && ret == 0 && len < MAX_STRING_SIZE);
876
877 pagefault_enable();
878 set_fs(old_fs);
(inlined by) process_fetch_insn_bottom at kernel/trace/trace_probe_tmpl.h:91
86 s3 = code;
87 stage3:
88 /* 3rd stage: store value to buffer */
89 if (unlikely(!dest)) {
90 if (code->op == FETCH_OP_ST_STRING) {
>91< ret += fetch_store_strlen(val + code->offset);
92 code++;
93 goto array;
94 } else
95 return -EILSEQ;
96 }
(inlined by) process_fetch_insn at kernel/trace/trace_kprobe.c:954
949 default:
950 return -EILSEQ;
951 }
952 code++;
953
>954< return process_fetch_insn_bottom(code, val, dest, base);
955 }
956 NOKPROBE_SYMBOL(process_fetch_insn)
957
958 /* Kprobe handler */
959 static nokprobe_inline void
process_fetch_insn+0x1a3/0x410:
adjust_stack_addr at kernel/trace/trace_uprobe.c:116
111 return addr - (n * sizeof(long));
112 }
113 #else
114 static unsigned long adjust_stack_addr(unsigned long addr, unsigned int n)
115 {
>116< return addr + (n * sizeof(long));
117 }
118 #endif
119
120 static unsigned long get_user_stack_nth(struct pt_regs *regs, unsigned int n)
121 {
(inlined by) get_user_stack_nth at kernel/trace/trace_uprobe.c:125
120 static unsigned long get_user_stack_nth(struct pt_regs *regs, unsigned int n)
121 {
122 unsigned long ret;
123 unsigned long addr = user_stack_pointer(regs);
124
>125< addr = adjust_stack_addr(addr, n);
126
127 if (copy_from_user(&ret, (void __force __user *) addr, sizeof(ret)))
128 return 0;
129
130 return ret;
(inlined by) process_fetch_insn at kernel/trace/trace_uprobe.c:212
207 switch (code->op) {
208 case FETCH_OP_REG:
209 val = regs_get_register(regs, code->param);
210 break;
211 case FETCH_OP_STACK:
>212< val = get_user_stack_nth(regs, code->param);
213 break;
214 case FETCH_OP_STACKP:
215 val = user_stack_pointer(regs);
216 break;
217 case FETCH_OP_RETVAL:
> -- Steve
>
>
--
Cheers,
Changbin Du
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