Messages in this thread Patch in this message | | | From | Masami Hiramatsu <> | Subject | [BUGFIX PATCH -tip] kprobes/x86: Fix to copy RIP relative instruction correctly | Date | Fri, 24 Aug 2018 02:16:12 +0900 |
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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 <mhiramat@kernel.org> Cc: stable@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;
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