Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

[Sourabh Jain <sourabhjain@linux.ibm.com>]

Hello Baoquan and Eric,


On 12/12/24 08:25, Baoquan he wrote:
> On 12/10/24 at 02:43pm, Sourabh Jain wrote:
>> kexec_elf_load() loads an ELF executable and sets the address of the
>> lowest PT_LOAD section to the address held by the lowest_load_addr
>> function argument.
>>
>> To determine the lowest PT_LOAD address, a local variable lowest_addr
>> (type unsigned long) is initialized to UINT_MAX. After loading each
>> PT_LOAD, its address is compared to lowest_addr. If a loaded PT_LOAD
>> address is lower, lowest_addr is updated. However, setting lowest_addr
>> to UINT_MAX won't work when the kernel image is loaded above 4G, as the
>> returned lowest PT_LOAD address would be invalid. This is resolved by
>> initializing lowest_addr to ULONG_MAX instead.
>>
>> This issue was discovered while implementing crashkernel high/low
>> reservation on the PowerPC architecture.
>>
>> Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
>> Cc: Baoquan he <bhe@redhat.com>
>> Cc: Hari Bathini <hbathini@linux.ibm.com>
>> CC: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: kexec@lists.infradead.org
>> Cc: linuxppc-dev@lists.ozlabs.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> ---
>>   kernel/kexec_elf.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/kexec_elf.c b/kernel/kexec_elf.c
>> index d3689632e8b9..3a5c25b2adc9 100644
>> --- a/kernel/kexec_elf.c
>> +++ b/kernel/kexec_elf.c
>> @@ -390,7 +390,7 @@ int kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
>>   			 struct kexec_buf *kbuf,
>>   			 unsigned long *lowest_load_addr)
>>   {
>> -	unsigned long lowest_addr = UINT_MAX;
>> +	unsigned long lowest_addr = ULONG_MAX;
> Great catch.
>
> Acked-by: Baoquan He <bhe@redhat.com>
Thank you for the Ack! The upcoming two patch series, which aim to 
enable generic crashkernel reservation, depends on this fix. One of them 
is already posted for upstream review: 
https://lore.kernel.org/all/20250108101458.406806-1-sourabhjain@linux.ibm.com/ 
I was wondering if you could guide us on how to get this fix pushed to 
the mainline tree.

Thanks,
Sourabh Jain