linux-kernel - Re: [PATCH 1/2] objtool/LoongArch: Restrict stack operation instruction

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Message-ID: <05ce0eba-22f6-ed0d-5005-227251decf50@loongson.cn>
Date: Tue, 30 Jul 2024 22:54:32 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Jinyang He <hejinyang@...ngson.cn>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] objtool/LoongArch: Restrict stack operation
 instruction

On 7/30/24 18:57, Jinyang He wrote:
> 
> On 2024-07-30 17:49, Tiezhu Yang wrote:
>> On 07/30/2024 05:28 PM, Jinyang He wrote:
>>> On 2024-07-30 14:19, Tiezhu Yang wrote:
>>>
>>>> After commit a0f7085f6a63 ("LoongArch: Add RANDOMIZE_KSTACK_OFFSET
>>>> support"), the code flow of do_syscall() was changed when compiled
>>>> with GCC due to the secondary stack of add_random_kstack_offset(),
>>>> something like this:
>>>>
>>>>    addi.d          $sp, $sp, -32
>>>>    st.d            $fp, $sp, 16
>>>>    st.d            $ra, $sp, 24
>>>>    addi.d          $fp, $sp, 32
>>>>    ...
>>>>    sub.d           $sp, $sp, $t1
>>> Have you checked the ORC info whether is right or tried backtrace which
>>> passed do_syscall? The "sub.d $sp, $sp, $t1" has modified the $sp so the
>>> $sp cannot express CFA here. This patch just clear the warning but 
>>> ignore
>>> the validity of ORC info. The wrong ORC info may cause illegally access
>>> memory when backtrace.
>>
>> I did testing many times before submitting, the call trace is
>> expected when testing "echo l > /proc/sysrq-trigger".
> Make sure the RANDOMIZE_KSTACK_OFFSET is enable. I tested it by
> CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y on qemu and it did
> not show the frame about handle_syscall.

I tested with the defconfig, CONFIG_RANDOMIZE_KSTACK_OFFSET is set but
CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT is not set, the call trace has
handle_syscall() which is the previous frame of do_syscall(), and the
orc dump info is correct.

Let me modify the config file and test again with the following configs:
CONFIG_RANDOMIZE_KSTACK_OFFSET=y CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT=y

If there exists problem, I will fix it.

Thanks,
Tiezhu