Since copy_optimized_instructions() misses to update real RIP
address while copying several instructions to working buffer,
it adjusts RIP-relative instruction with wrong RIP address for
the 2nd and subsequent instructions.
This may break the kernel (like kernel freeze) because
probed instruction can refer a wrong data. For example,
putting kprobes on cpumask_next hit this bug.
cpumask_next is normally like below if CONFIG_CPUMASK_OFFSTACK=y
(in this case nr_cpumask_bits is an alias of nr_cpu_ids)
<cpumask_next>:
48 89 f0 mov %rsi,%rax
8b 35 7b fb e2 00 mov 0xe2fb7b(%rip),%esi
# ffffffff82db9e64 <nr_cpu_ids>
55 push %rbp
...
If we put a kprobe on it and optimized with jump, it becomes
like this.
e9 95 7d 07 1e jmpq 0xffffffffa000207a
7b fb jnp 0xffffffff81f8a2e2 <cpumask_next+2>
e2 00 loop 0xffffffff81f8a2e9 <cpumask_next+9>
55 push %rbp
This shows first 2 "mov" instructions are copied to trampoline
buffer at 0xffffffffa000207a. Here is the disassembled result.
(skipped optprobe template instructions)
Dump of assembler code from 0xffffffffa000207a to 0xffffffffa00020ea:
54 push %rsp
...
48 83 c4 08 add $0x8,%rsp
9d popfq
48 89 f0 mov %rsi,%rax
8b 35 82 7d db e2 mov -0x1d24827e(%rip),%esi
# 0xffffffff82db9e67 <nr_cpu_ids+3>
As it shows, the 2nd mov accesses *(nr_cpu_ids+3) instead of
*nr_cpu_ids. This leads a kernel freeze because cpumask_next()
always returns 0 and for_each_cpu() never ended.
Fixing this by adding len correctly to real RIP address while
copying.
Fixes: 63fef14fc98a ("kprobes/x86: Make insn buffer always ROX and use
text_poke()")
Reported-by: Michael Rodin <michael@rodin.online>
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
Cc: sta...@vger.kernel.org
---
arch/x86/kernel/kprobes/opt.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index eaf02f2e7300..e92672b8b490 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -189,7 +189,8 @@ static int copy_optimized_instructions(u8 *dest, u8 *src,
u8 *real)
int len = 0, ret;
while (len < RELATIVEJUMP_SIZE) {
- ret = __copy_instruction(dest + len, src + len, real, &insn);
+ ret = __copy_instruction(dest + len, src + len, real + len,
+ &insn);
if (!ret || !can_boost(&insn, src + len))
return -EINVAL;
len += ret;
