On 06/03/2012 02:59 PM, tiejun.chen wrote:
> On 06/03/2012 01:07 PM, Tiejun Chen wrote:
>> We don't do the real store operation for kprobing 'stwu Rx,(y)R1'
>> since this may corrupt the exception frame, now we will do this
>> operation safely in exception return code after migrate current
>> exception frame below the kprobed function stack.
>>
>> So we only update gpr[1] here and trigger a thread flag to mask
>> this.
>>
>> Note we should make sure if we trigger kernel stack over flow.
>>
>> Signed-off-by: Tiejun Chen <tiejun.c...@windriver.com>
>> ---
>>  arch/powerpc/lib/sstep.c |   37 +++++++++++++++++++++++++++++++++++--
>>  1 files changed, 35 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
>> index 9a52349..a4ce463 100644
>> --- a/arch/powerpc/lib/sstep.c
>> +++ b/arch/powerpc/lib/sstep.c
>> @@ -566,7 +566,7 @@ int __kprobes emulate_step(struct pt_regs *regs, 
>> unsigned int instr)
>>      unsigned long int ea;
>>      unsigned int cr, mb, me, sh;
>>      int err;
>> -    unsigned long old_ra;
>> +    unsigned long old_ra, val3, r1;
>>      long ival;
>>  
>>      opcode = instr >> 26;
>> @@ -1486,11 +1486,44 @@ int __kprobes emulate_step(struct pt_regs *regs, 
>> unsigned int instr)
>>              goto ldst_done;
>>  
>>      case 36:        /* stw */
>> -    case 37:        /* stwu */
>>              val = regs->gpr[rd];
>>              err = write_mem(val, dform_ea(instr, regs), 4, regs);
>>              goto ldst_done;
>>  
>> +    case 37:        /* stwu */
>> +            __asm__ __volatile__("mr %0,1" : "=r" (r1) :);
> 
> I'll remove this line, please see below.
> 
>> +
>> +            val = regs->gpr[rd];
>> +            val3 = dform_ea(instr, regs);
>> +            /*
>> +             * For PPC32 we always use stwu to change stack point with r1. 
>> So
>> +             * this emulated store may corrupt the exception frame, now we
>> +             * have to provide the exception frame trampoline, which is 
>> pushed
>> +             * below the kprobed function stack. So we only update gpr[1] 
>> but
>> +             * don't emulate the real store operation. We will do real store
>> +             * operation safely in exception return code by checking this 
>> flag.
>> +             */
>> +            if ((ra == 1) && !(regs->msr & MSR_PR) && (val3 >= r1)) {

And I also should change

(val3 >= r1) to (val3 >= (regs->r1 - STACK_INT_FRAME_SIZE)) since its worth
doing this only we'll really overwrite this exception stack.

Tiejun

>> +                    /*
>> +                     * Check if we will touch kernel sack overflow
>> +                     */
>> +                    if (r1 - STACK_INT_FRAME_SIZE <= 
>> current->thread.ksp_limit) {
> 
> OOPS. This line should be:
>                       
>               if (val3 - STACK_INT_FRAME_SIZE <= current->thread.ksp_limit) {
> 
> Tiejun
> 
>> +                            printk(KERN_CRIT "Can't kprobe this since 
>> Kernel stack overflow.\n");
>> +                            err = -EINVAL;
>> +                            break;
>> +                    }
>> +
>> +                    /*
>> +                     * Check if we already set since that means we'll
>> +                     * lose the previous value.
>> +                     */
>> +                    WARN_ON(test_thread_flag(TIF_EMULATE_STACK_STORE));
>> +                    set_thread_flag(TIF_EMULATE_STACK_STORE);
>> +                    err = 0;
>> +            } else
>> +                    err = write_mem(val, val3, 4, regs);
>> +            goto ldst_done;
>> +
>>      case 38:        /* stb */
>>      case 39:        /* stbu */
>>              val = regs->gpr[rd];
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
> 
> 

_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev

Reply via email to