Message ID | 20190507085006.17500-2-po-hsu.lin@canonical.com |
---|---|
State | New |
Headers | show |
Series | Fix for ftrace test hang issue | expand |
On 5/7/19 10:50 AM, Po-Hsu Lin wrote: > From: Masami Hiramatsu <mhiramat@kernel.org> > > BugLink: https://bugs.launchpad.net/bugs/1826385 > > 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> > (cherry picked from commit 43a1b0cb4cd6dbfd3cd9c10da663368394d299d8) > Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com> Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com> > --- > arch/x86/kernel/kprobes/opt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c > index 1467f96..72e1286 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;
On 5/7/19 1:50 AM, Po-Hsu Lin wrote: > From: Masami Hiramatsu <mhiramat@kernel.org> > > BugLink: https://bugs.launchpad.net/bugs/1826385 > > 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> > (cherry picked from commit 43a1b0cb4cd6dbfd3cd9c10da663368394d299d8) > Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com> > --- Acked-by: Connor Kuehl <connor.kuehl@canonical.com> > arch/x86/kernel/kprobes/opt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c > index 1467f96..72e1286 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; >
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 1467f96..72e1286 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;