diff options
| author | Li Huafei <lihuafei1@huawei.com> | 2022-09-23 17:32:53 +0800 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2022-09-28 22:19:52 +1000 |
| commit | 97f88a3d723162781d6cbfdc7b9617eefab55b19 (patch) | |
| tree | 81355948f66131ff13ef0fd402e3aff5b4347ff1 | |
| parent | 5e4952656bca1b5d8c2be36682dc66d844797ad2 (diff) | |
powerpc/kprobes: Fix null pointer reference in arch_prepare_kprobe()
I found a null pointer reference in arch_prepare_kprobe():
# echo 'p cmdline_proc_show' > kprobe_events
# echo 'p cmdline_proc_show+16' >> kprobe_events
Kernel attempted to read user page (0) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on read at 0x00000000
Faulting instruction address: 0xc000000000050bfc
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 122 Comm: sh Not tainted 6.0.0-rc3-00007-gdcf8e5633e2e #10
NIP: c000000000050bfc LR: c000000000050bec CTR: 0000000000005bdc
REGS: c0000000348475b0 TRAP: 0300 Not tainted (6.0.0-rc3-00007-gdcf8e5633e2e)
MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE> CR: 88002444 XER: 20040006
CFAR: c00000000022d100 DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 0
...
NIP arch_prepare_kprobe+0x10c/0x2d0
LR arch_prepare_kprobe+0xfc/0x2d0
Call Trace:
0xc0000000012f77a0 (unreliable)
register_kprobe+0x3c0/0x7a0
__register_trace_kprobe+0x140/0x1a0
__trace_kprobe_create+0x794/0x1040
trace_probe_create+0xc4/0xe0
create_or_delete_trace_kprobe+0x2c/0x80
trace_parse_run_command+0xf0/0x210
probes_write+0x20/0x40
vfs_write+0xfc/0x450
ksys_write+0x84/0x140
system_call_exception+0x17c/0x3a0
system_call_vectored_common+0xe8/0x278
--- interrupt: 3000 at 0x7fffa5682de0
NIP: 00007fffa5682de0 LR: 0000000000000000 CTR: 0000000000000000
REGS: c000000034847e80 TRAP: 3000 Not tainted (6.0.0-rc3-00007-gdcf8e5633e2e)
MSR: 900000000280f033 <SF,HV,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE> CR: 44002408 XER: 00000000
The address being probed has some special:
cmdline_proc_show: Probe based on ftrace
cmdline_proc_show+16: Probe for the next instruction at the ftrace location
The ftrace-based kprobe does not generate kprobe::ainsn::insn, it gets
set to NULL. In arch_prepare_kprobe() it will check for:
...
prev = get_kprobe(p->addr - 1);
preempt_enable_no_resched();
if (prev && ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) {
...
If prev is based on ftrace, 'ppc_inst_read(prev->ainsn.insn)' will occur
with a null pointer reference. At this point prev->addr will not be a
prefixed instruction, so the check can be skipped.
Check if prev is ftrace-based kprobe before reading 'prev->ainsn.insn'
to fix this problem.
Fixes: b4657f7650ba ("powerpc/kprobes: Don't allow breakpoints on suffixes")
Signed-off-by: Li Huafei <lihuafei1@huawei.com>
[mpe: Trim oops]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220923093253.177298-1-lihuafei1@huawei.com
| -rw-r--r-- | arch/powerpc/kernel/kprobes.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index 912d4f8a13be..bd7b1a035459 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -161,7 +161,13 @@ int arch_prepare_kprobe(struct kprobe *p) preempt_disable(); prev = get_kprobe(p->addr - 1); preempt_enable_no_resched(); - if (prev && ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) { + + /* + * When prev is a ftrace-based kprobe, we don't have an insn, and it + * doesn't probe for prefixed instruction. + */ + if (prev && !kprobe_ftrace(prev) && + ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) { printk("Cannot register a kprobe on the second word of prefixed instruction\n"); ret = -EINVAL; } |