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

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Message-ID: <6ee45e77-eb22-c4ac-ee47-6a329236eeb7@loongson.cn>
Date: Tue, 30 Jul 2024 17:49:14 +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 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".

Thanks,
Tiezhu