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authorMasami Hiramatsu <mhiramat@kernel.org>2018-08-24 02:16:12 +0900
committerIngo Molnar <mingo@kernel.org>2018-12-04 09:35:20 +0100
commit43a1b0cb4cd6dbfd3cd9c10da663368394d299d8 (patch)
parent2595646791c319cadfdbf271563aac97d0843dc7 (diff)
kprobes/x86: Fix instruction patching corruption when copying more than one RIP-relative instruction
After copy_optimized_instructions() copies several instructions to the working buffer it tries to fix up the real RIP address, but it adjusts the RIP-relative instruction with an incorrect RIP address for the 2nd and subsequent instructions due to a bug in the logic. This will break the kernel pretty badly (with likely outcomes such as a kernel freeze, a crash, or worse) because probed instructions can refer to the wrong data. For example putting kprobes on cpumask_next() typically hits 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 it gets jump-optimized, it gets patched by the kprobes code like this: <cpumask_next>: 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 that the first two MOV instructions were copied to a trampoline buffer at 0xffffffffa000207a. Here is the disassembled result of the trampoline, skipping the optprobe template instructions: # Dump of assembly 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> This dump shows that the second MOV accesses *(nr_cpu_ids+3) instead of the original *nr_cpu_ids. This leads to a kernel freeze because cpumask_next() always returns 0 and for_each_cpu() never ends. Fix this by adding 'len' correctly to the real RIP address while copying. [ mingo: Improved the changelog. ] Reported-by: Michael Rodin <michael@rodin.online> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org # v4.15+ Fixes: 63fef14fc98a ("kprobes/x86: Make insn buffer always ROX and use text_poke()") Link: http://lkml.kernel.org/r/153504457253.22602.1314289671019919596.stgit@devbox Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 40b16b270656..6adf6e6c2933 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -189,7 +189,7 @@ 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;