linux-kernel - Re: [PATCH v2 2/3] vmcore: allow fadump to export vmcore even if is_kdump

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ad792aec-412e-27da-f39e-fd9c208ba154@linux.ibm.com>
Date:   Tue, 12 Sep 2023 14:01:14 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     Baoquan He <bhe@...hat.com>, Michael Ellerman <mpe@...erman.id.au>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Dave Young <dyoung@...hat.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>
Subject: Re: [PATCH v2 2/3] vmcore: allow fadump to export vmcore even if
 is_kdump_kernel() is false



On 11/09/23 4:01 pm, Baoquan He wrote:
> On 09/11/23 at 05:13pm, Michael Ellerman wrote:
>> Hari Bathini <hbathini@...ux.ibm.com> writes:
>>> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
>>> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
>>> alternate dump capturing methods like fadump [1] also set it to export
>>> the vmcore. Since, is_kdump_kernel() is used to restrict resources in
>>> crash dump capture kernel and such restrictions are not desirable for
>>> fadump, allow is_kdump_kernel() to be defined differently for fadump
>>> case. With that change, include is_fadump_active() check in functions
>>> is_vmcore_usable() & vmcore_unusable() to be able to export vmcore for
>>> fadump case too.
>> ...
>>> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
>>> index 0f3a656293b0..de8a9fabfb6f 100644
>>> --- a/include/linux/crash_dump.h
>>> +++ b/include/linux/crash_dump.h
>>> @@ -50,6 +50,7 @@ void vmcore_cleanup(void);
>>>   #define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
>>>   #endif
>>>   
>>> +#ifndef is_kdump_kernel
>>>   /*
>>>    * is_kdump_kernel() checks whether this kernel is booting after a panic of
>>>    * previous kernel or not. This is determined by checking if previous kernel
>>> @@ -64,6 +65,19 @@ static inline bool is_kdump_kernel(void)
>>>   {
>>>   	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
>>>   }
>>> +#endif
>>> +
>>> +#ifndef is_fadump_active
>>> +/*
>>> + * If f/w assisted dump capturing mechanism (fadump), instead of kexec based
>>> + * dump capturing mechanism (kdump) is exporting the vmcore, then this function
>>> + * will be defined in arch specific code to return true, when appropriate.
>>> + */
>>> +static inline bool is_fadump_active(void)
>>> +{
>>> +	return false;
>>> +}
>>> +#endif
>>>   
>>>   /* is_vmcore_usable() checks if the kernel is booting after a panic and
>>>    * the vmcore region is usable.
>>> @@ -75,7 +89,8 @@ static inline bool is_kdump_kernel(void)
>>>   
>>>   static inline int is_vmcore_usable(void)
>>>   {
>>> -	return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
>>> +	return (is_kdump_kernel() || is_fadump_active())
>>> +		&& elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
>>>   }
>>>   
>>>   /* vmcore_unusable() marks the vmcore as unusable,
>>> @@ -84,7 +99,7 @@ static inline int is_vmcore_usable(void)
>>>   
>>>   static inline void vmcore_unusable(void)
>>>   {
>>> -	if (is_kdump_kernel())
>>> +	if (is_kdump_kernel() || is_fadump_active())
>>>   		elfcorehdr_addr = ELFCORE_ADDR_ERR;
>>>   }
>>
>> I think it would be cleaner to decouple is_vmcore_usable() and
>> vmcore_usable() from is_kdump_kernel().
>>
>> ie, make them operate solely based on the value of elforehdr_addr:
>>
>> static inline int is_vmcore_usable(void)
>> {
>> 	elfcorehdr_addr != ELFCORE_ADDR_ERR && \
>> 		elfcorehdr_addr != ELFCORE_ADDR_MAX;
> 
> Agree. I fell into the blind corner of thinking earlier. Above change
> is better.

Thanks for the reviews.
Posted v3.

- Hari