linux-kernel - Re: [PATCH] kexec: Initialize ELF lowest address to ULONG

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Message-ID: <5c814eef-b4e4-4afc-a394-c17857da8a07@linux.ibm.com>
Date: Thu, 9 Jan 2025 11:02:08 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Baoquan he <bhe@...hat.com>, ebiederm@...ssion.com,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

Hello Andrew,

On 09/01/25 10:58, Andrew Morton wrote:
> On Thu, 9 Jan 2025 09:42:14 +0530 Sourabh Jain <sourabhjain@...ux.ibm.com> wrote:
>
>> 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@...hat.com>
>>>> Cc: Hari Bathini <hbathini@...ux.ibm.com>
>>>> CC: Madhavan Srinivasan <maddy@...ux.ibm.com>
>>>> Cc: Michael Ellerman <mpe@...erman.id.au>
>>>> Cc: kexec@...ts.infradead.org
>>>> Cc: linuxppc-dev@...ts.ozlabs.org
>>>> Cc: linux-kernel@...r.kernel.org
>>>> Signed-off-by: Sourabh Jain <sourabhjain@...ux.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@...hat.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.
> Please include this patch (with Baoquan's ack) in whichever tree
> contains the powerpc patches which depend upon it.

Sure, I will include this patch in the respective patch series.

Thanks,
Sourabh Jain