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;
 	int ret;
 	size_t i;
 
-- 
2.47.1

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>

>  	int ret;
>  	size_t i;
>  
> -- 
> 2.47.1
>

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>

Thanks for the Ack Baoquan.

- Sourabh Jain