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[PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

Sourabh Jain posted 1 patch 1 month, 2 weeks ago 
kernel/kexec_elf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Sourabh Jain 1 month, 2 weeks ago 
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
Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Baoquan he 1 month, 2 weeks ago 
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
>
Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Sourabh Jain 2 weeks, 3 days ago 
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
Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Andrew Morton 2 weeks, 3 days ago 
On Thu, 9 Jan 2025 09:42:14 +0530 Sourabh Jain <sourabhjain@linux.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@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.

Please include this patch (with Baoquan's ack) in whichever tree
contains the powerpc patches which depend upon it.
Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Sourabh Jain 2 weeks, 3 days ago 
Hello Andrew,

On 09/01/25 10:58, Andrew Morton wrote:
> On Thu, 9 Jan 2025 09:42:14 +0530 Sourabh Jain <sourabhjain@linux.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@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.
> 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
Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX
Posted by Sourabh Jain 1 month, 2 weeks ago 
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

Patchew 2.1-devel-b67e4c2

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