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Message-ID: <9b1d1d42-ecc9-8d0d-b616-849b0b368d67@huawei.com> Date: Mon, 2 Mar 2020 17:37:09 +0800 From: Jason Yan <yanaijie@...wei.com> To: Scott Wood <oss@...error.net>, Daniel Axtens <dja@...ens.net>, <mpe@...erman.id.au>, <linuxppc-dev@...ts.ozlabs.org>, <diana.craciun@....com>, <christophe.leroy@....fr>, <benh@...nel.crashing.org>, <paulus@...ba.org>, <npiggin@...il.com>, <keescook@...omium.org>, <kernel-hardening@...ts.openwall.com>, <me@...in.cc> CC: <linux-kernel@...r.kernel.org>, <zhaohongjiang@...wei.com> Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64 在 2020/3/2 16:47, Scott Wood 写道: > On Mon, 2020-03-02 at 15:12 +0800, Jason Yan wrote: >> >> 在 2020/3/2 11:24, Scott Wood 写道: >>> On Mon, 2020-03-02 at 10:17 +0800, Jason Yan wrote: >>>> >>>> 在 2020/3/1 6:54, Scott Wood 写道: >>>>> On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote: >>>>>> >>>>>> Turnning to %p may not be a good idea in this situation. So >>>>>> for the REG logs printed when dumping stack, we can disable it when >>>>>> KASLR is open. For the REG logs in other places like show_regs(), >>>>>> only >>>>>> privileged can trigger it, and they are not combind with a symbol, >>>>>> so >>>>>> I think it's ok to keep them. >>>>>> >>>>>> diff --git a/arch/powerpc/kernel/process.c >>>>>> b/arch/powerpc/kernel/process.c >>>>>> index fad50db9dcf2..659c51f0739a 100644 >>>>>> --- a/arch/powerpc/kernel/process.c >>>>>> +++ b/arch/powerpc/kernel/process.c >>>>>> @@ -2068,7 +2068,10 @@ void show_stack(struct task_struct *tsk, >>>>>> unsigned >>>>>> long *stack) >>>>>> newsp = stack[0]; >>>>>> ip = stack[STACK_FRAME_LR_SAVE]; >>>>>> if (!firstframe || ip != lr) { >>>>>> - printk("["REG"] ["REG"] %pS", sp, ip, (void >>>>>> *)ip); >>>>>> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) >>>>>> + printk("%pS", (void *)ip); >>>>>> + else >>>>>> + printk("["REG"] ["REG"] %pS", sp, >>>>>> ip, >>>>>> (void *)ip); >>>>> >>>>> This doesn't deal with "nokaslr" on the kernel command line. It also >>>>> doesn't >>>>> seem like something that every callsite should have to opencode, >>>>> versus >>>>> having >>>>> an appropriate format specifier behaves as I described above (and I >>>>> still >>>>> don't see why that format specifier should not be "%p"). >>>>> >>>> >>>> Actually I still do not understand why we should print the raw value >>>> here. When KALLSYMS is enabled we have symbol name and offset like >>>> put_cred_rcu+0x108/0x110, and when KALLSYMS is disabled we have the raw >>>> address. >>> >>> I'm more concerned about the stack address for wading through a raw stack >>> dump >>> (to find function call arguments, etc). The return address does help >>> confirm >>> that I'm on the right stack frame though, and also makes looking up a line >>> number slightly easier than having to look up a symbol address and then >>> add >>> the offset (at least for non-module addresses). >>> >>> As a random aside, the mismatch between Linux printing a hex offset and >>> GDB >>> using decimal in disassembly is annoying... >>> >> >> OK, I will send a RFC patch to add a new format specifier such as "%pk" >> or change the exsiting "%pK" to print raw value of addresses when KASLR >> is disabled and print hash value of addresses when KASLR is enabled. >> Let's see what the printk guys would say :) > > I'm not sure that a new format specifier is needed versus changing the > behavior of "%p", and "%pK" definitely doesn't seem suitable given that it's > intended to be more restricted than "%p" (see commit ef0010a30935de4). The > question is whether there is a legitimate reason to hash in the absence of > kaslr. > The problem is that if we change the behavior of "%p", we have to turn all exsiting "%p" to "%pK". Hashing is still reasonable when there is no kaslr because some architectures support randomize at build time such as arm64. > -Scott > > > > . >
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