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)) {
> + /*
> + * 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];
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