On 2014/7/29 19:36, Masami Hiramatsu wrote: > Hi Wang, > > (2014/07/29 10:55), Wang Nan wrote: >> On 2014/7/29 9:43, Masami Hiramatsu wrote: >>> (2014/07/28 21:20), Wang Nan wrote: >>>> This patch frees optinsn slot when range check error to prevent memory >>>> leaks. Before this patch, cache entry in kprobe_insn_cache won't be >>>> freed if kprobe optimizing fails due to range check failure. >>>> >>>> Signed-off-by: Wang Nan <wangn...@huawei.com> >>> >>> Oops, thank you for finding it! >>> >>> Acked-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com> >>> >>> BTW, would you really have hit this error? >>> I'd like to know the case if this really happens. >> >> I'm not really hit it on x86_64. I found this problem when trying to >> implement kprobe opt on arm. > > That's interesting :) > >> >> On arm, relative jump can only branch on/backward 64MB, which makes it a >> realistic problem. > > Yeah, that is what I expected on RISC processor such as ARM. > > Perhaps you'll need to overwrite 2 words, one is for "ldr pc, [pc, #-4]" and > one is for > the address data. In this case, you have no branch range limitation in 32bit > mode. This > requires branch destination checking for safety as x86 optprobe does. > Plus, you'll have to use same technique of x86 to make a detour code and > deferred > optimization for overwriting multiple instructions. Put a breakpoint at the > probe point, > wait for synchronize_sched(), put the 2nd instruction(.data) and overwrite > the breakpoint > with the "ldr". :) > > However, that is only for arm32. > For ARM64, I'm not so sure about its ISA. I guess we need a scratchpad area > for that.. > > Anyway, please CC to me when you've done the prototyping and sending RFC. > I'll review > and test it. :) > > Thank you, >
Hi Masami, I have posted my RFC patch on LKML and ARM mailing list, and also CC you. Please see: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-August/277809.html Please help me review my patch, Thank you! >> >>> >>>> --- >>>> arch/x86/kernel/kprobes/opt.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c >>>> index f304773..f1314d0 100644 >>>> --- a/arch/x86/kernel/kprobes/opt.c >>>> +++ b/arch/x86/kernel/kprobes/opt.c >>>> @@ -338,8 +338,10 @@ int arch_prepare_optimized_kprobe(struct >>>> optimized_kprobe *op) >>>> * a relative jump. >>>> */ >>>> rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE; >>>> - if (abs(rel) > 0x7fffffff) >>>> + if (abs(rel) > 0x7fffffff) { >>>> + __arch_remove_optimized_kprobe(op, 0); >>>> return -ERANGE; >>>> + } >>>> >>>> buf = (u8 *)op->optinsn.insn; >>>> >>>> >>> >>> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majord...@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
