linux-kernel - Re: [PATCH v2 1/6] kexec: Initialize ELF lowest address to ULONG

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Message-ID: <7cfe94c9-4ca5-48b1-ab53-bc08fcf8fbc0@linux.ibm.com>
Date: Thu, 23 Jan 2025 15:34:11 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v2 1/6] kexec: Initialize ELF lowest address to ULONG_MAX



On 21/01/25 5:24 pm, 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.
> 

Acked-by: Hari Bathini <hbathini@...ux.ibm.com>

> Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Mahesh Salgaonkar <mahesh@...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
> Acked-by: Baoquan He <bhe@...hat.com>
> 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;
>   	int ret;
>   	size_t i;
>