In memmap_exclude_ranges(), there will exclude elfheader from
crashk_res. In the current x86 architecture code, the elfheader is
always allocated at crashk_res.start. It seems that there won't be a
split a new range. But it depends on the allocation position of
elfheader in crashk_res. To avoid potential out of bounds in future, Set
the array size to 2.

But similar issue will not exist in fill_up_crash_elf_data(). Because
the range to be excluded is [0, 1M], start (0) is special and will not
appear in the middle of existing cmem->ranges[]. I added a comment to
explain it.

Signed-off-by: fuqiang wang <fuqiang.wang@easystack.cn>
---
 arch/x86/kernel/crash.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..1c15d0884c90 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -149,6 +149,13 @@ static struct crash_mem *fill_up_crash_elf_data(void)
 	/*
 	 * Exclusion of crash region and/or crashk_low_res may cause
 	 * another range split. So add extra two slots here.
+	 *
+	 * Exclusion of low 1M may not cause another range split, because the
+	 * range of exclude is [0, 1M] and the condition for splitting a new
+	 * region is that the start, end parameters are both in a certain
+	 * existing region in cmem and cannot be equal to existing region's
+	 * start or end. Obviously, the start of [0, 1M] cannot meet this
+	 * condition.
 	 */
 	nr_ranges += 2;
 	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
@@ -282,9 +289,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 	struct crash_memmap_data cmd;
 	struct crash_mem *cmem;
 
-	cmem = vzalloc(struct_size(cmem, ranges, 1));
+	cmem = vzalloc(struct_size(cmem, ranges, 2));
 	if (!cmem)
 		return -ENOMEM;
+	cmem->max_nr_ranges = 2;
+
+	/* Exclude some ranges from crashk_res and add rest to memmap */
+	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
+	if (ret)
+		goto out;
 
 	memset(&cmd, 0, sizeof(struct crash_memmap_data));
 	cmd.params = params;
@@ -320,11 +333,6 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 		add_e820_entry(params, &ei);
 	}
 
-	/* Exclude some ranges from crashk_res and add rest to memmap */
-	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
-	if (ret)
-		goto out;
-
 	for (i = 0; i < cmem->nr_ranges; i++) {
 		ei.size = cmem->ranges[i].end - cmem->ranges[i].start + 1;
 
-- 
2.42.0

On 12/20/23 at 01:57pm, fuqiang wang wrote:
> In memmap_exclude_ranges(), there will exclude elfheader from
> crashk_res. In the current x86 architecture code, the elfheader is
> always allocated at crashk_res.start. It seems that there won't be a
> split a new range. But it depends on the allocation position of
> elfheader in crashk_res. To avoid potential out of bounds in future, Set
> the array size to 2.

If so, I would suggest to add extra slot for low 1M too in
fill_up_crash_elf_data() lest the low 1M could be changed in the future,
e.g [start, 1M].

> 
> But similar issue will not exist in fill_up_crash_elf_data(). Because
> the range to be excluded is [0, 1M], start (0) is special and will not
> appear in the middle of existing cmem->ranges[]. I added a comment to
> explain it.
> 
> Signed-off-by: fuqiang wang <fuqiang.wang@easystack.cn>
> ---
>  arch/x86/kernel/crash.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index c92d88680dbf..1c15d0884c90 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -149,6 +149,13 @@ static struct crash_mem *fill_up_crash_elf_data(void)
>  	/*
>  	 * Exclusion of crash region and/or crashk_low_res may cause
>  	 * another range split. So add extra two slots here.
> +	 *
> +	 * Exclusion of low 1M may not cause another range split, because the
> +	 * range of exclude is [0, 1M] and the condition for splitting a new
> +	 * region is that the start, end parameters are both in a certain
> +	 * existing region in cmem and cannot be equal to existing region's
> +	 * start or end. Obviously, the start of [0, 1M] cannot meet this
> +	 * condition.
>  	 */
>  	nr_ranges += 2;
>  	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
> @@ -282,9 +289,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>  	struct crash_memmap_data cmd;
>  	struct crash_mem *cmem;
>  
> -	cmem = vzalloc(struct_size(cmem, ranges, 1));
> +	cmem = vzalloc(struct_size(cmem, ranges, 2));
>  	if (!cmem)
>  		return -ENOMEM;
> +	cmem->max_nr_ranges = 2;
> +
> +	/* Exclude some ranges from crashk_res and add rest to memmap */
> +	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
> +	if (ret)
> +		goto out;
>  
>  	memset(&cmd, 0, sizeof(struct crash_memmap_data));
>  	cmd.params = params;
> @@ -320,11 +333,6 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>  		add_e820_entry(params, &ei);
>  	}
>  
> -	/* Exclude some ranges from crashk_res and add rest to memmap */
> -	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
> -	if (ret)
> -		goto out;

And you didn't mention moving above code block up in log. I would
suggest keeping it as is because it looks more reasonable to be adjacent
to the following cmem->ranges[] handling.

> -
>  	for (i = 0; i < cmem->nr_ranges; i++) {
>  		ei.size = cmem->ranges[i].end - cmem->ranges[i].start + 1;
>  
> -- 
> 2.42.0
>

在 2023/12/21 21:14, Baoquan He 写道:

> On 12/20/23 at 01:57pm, fuqiang wang wrote:
>> In memmap_exclude_ranges(), there will exclude elfheader from
>> crashk_res. In the current x86 architecture code, the elfheader is
>> always allocated at crashk_res.start. It seems that there won't be a
>> split a new range. But it depends on the allocation position of
>> elfheader in crashk_res. To avoid potential out of bounds in future, Set
>> the array size to 2.
> If so, I would suggest to add extra slot for low 1M too in
> fill_up_crash_elf_data() lest the low 1M could be changed in the future,
> e.g [start, 1M].


Hi Baoquan

This seems to be better for future maintenance. Thank you for your suggestion.

>> But similar issue will not exist in fill_up_crash_elf_data(). Because
>> the range to be excluded is [0, 1M], start (0) is special and will not
>> appear in the middle of existing cmem->ranges[]. I added a comment to
>> explain it.
>>
>> Signed-off-by: fuqiang wang <fuqiang.wang@easystack.cn>
>> ---
>>   arch/x86/kernel/crash.c | 20 ++++++++++++++------
>>   1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index c92d88680dbf..1c15d0884c90 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -149,6 +149,13 @@ static struct crash_mem *fill_up_crash_elf_data(void)
>>   	/*
>>   	 * Exclusion of crash region and/or crashk_low_res may cause
>>   	 * another range split. So add extra two slots here.
>> +	 *
>> +	 * Exclusion of low 1M may not cause another range split, because the
>> +	 * range of exclude is [0, 1M] and the condition for splitting a new
>> +	 * region is that the start, end parameters are both in a certain
>> +	 * existing region in cmem and cannot be equal to existing region's
>> +	 * start or end. Obviously, the start of [0, 1M] cannot meet this
>> +	 * condition.
>>   	 */
>>   	nr_ranges += 2;
>>   	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
>> @@ -282,9 +289,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>>   	struct crash_memmap_data cmd;
>>   	struct crash_mem *cmem;
>>   
>> -	cmem = vzalloc(struct_size(cmem, ranges, 1));
>> +	cmem = vzalloc(struct_size(cmem, ranges, 2));
>>   	if (!cmem)
>>   		return -ENOMEM;
>> +	cmem->max_nr_ranges = 2;
>> +
>> +	/* Exclude some ranges from crashk_res and add rest to memmap */
>> +	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
>> +	if (ret)
>> +		goto out;
>>   
>>   	memset(&cmd, 0, sizeof(struct crash_memmap_data));
>>   	cmd.params = params;
>> @@ -320,11 +333,6 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>>   		add_e820_entry(params, &ei);
>>   	}
>>   
>> -	/* Exclude some ranges from crashk_res and add rest to memmap */
>> -	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
>> -	if (ret)
>> -		goto out;
> And you didn't mention moving above code block up in log. I would
> suggest keeping it as is because it looks more reasonable to be adjacent
> to the following cmem->ranges[] handling.

Yes, baoquan, keeping it as it is may be more coherent.I will post a new patch later.

Thanks
fuqiang

>> -
>>   	for (i = 0; i < cmem->nr_ranges; i++) {
>>   		ei.size = cmem->ranges[i].end - cmem->ranges[i].start + 1;
>>   
>> -- 
>> 2.42.0
>>