linux-kernel - Re: [PATCH v12 3/9] kexec: define functions to map and unmap segments

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Message-ID: <95d249ef-bfb3-431f-b633-8b3de383e067@linux.microsoft.com>
Date: Sun, 20 Apr 2025 05:30:33 -0700
From: steven chen <chenste@...ux.microsoft.com>
To: Baoquan He <bhe@...hat.com>
Cc: zohar@...ux.ibm.com, stefanb@...ux.ibm.com,
 roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
 eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
 code@...icks.com, bauermann@...abnow.com, linux-integrity@...r.kernel.org,
 kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
 linux-kernel@...r.kernel.org, madvenka@...ux.microsoft.com,
 nramas@...ux.microsoft.com, James.Bottomley@...senpartnership.com,
 vgoyal@...hat.com, dyoung@...hat.com
Subject: Re: [PATCH v12 3/9] kexec: define functions to map and unmap segments

On 4/17/2025 9:36 PM, Baoquan He wrote:
> On 04/15/25 at 07:10pm, steven chen wrote:
>> From: Steven Chen <chenste@...ux.microsoft.com>
>   ^^^^^^
>> Implement kimage_map_segment() to enable IMA to map the measurement log
>> list to the kimage structure during the kexec 'load' stage. This function
>> gathers the source pages within the specified address range, and maps them
>> to a contiguous virtual address range.
>>
>> This is a preparation for later usage.
>>
>> Implement kimage_unmap_segment() for unmapping segments using vunmap().
>>
>> From: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>    ^^^^^^
>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>    ^^^^^^^
>> Cc: Eric Biederman <ebiederm@...ssion.com>
>> Cc: Baoquan He <bhe@...hat.com>
>> Cc: Vivek Goyal <vgoyal@...hat.com>
>> Cc: Dave Young <dyoung@...hat.com>
>> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
>    ^^^^^
>
> The signing on this patch is a little confusing. I can't see who is the
> real author, who is the co-author, between you and Tushar. You may need
> to refer to Documentation/process/5.Posting.rst to make that clear.

Hi Baoquan,

 From my understanding, if there is no change from the original author 
patch, need to add
 From tag and Signed-off-by tag; otherwise, if there are changes, 
Signed-off-by can be used.

Thanks,

Steven

>> Acked-by: Baoquan He <bhe@...hat.com>
>> ---
>>   include/linux/kexec.h |  6 +++++
>>   kernel/kexec_core.c   | 54 +++++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 60 insertions(+)
>>
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index f0e9f8eda7a3..7d6b12f8b8d0 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -467,13 +467,19 @@ extern bool kexec_file_dbg_print;
>>   #define kexec_dprintk(fmt, arg...) \
>>           do { if (kexec_file_dbg_print) pr_info(fmt, ##arg); } while (0)
>>   
>> +extern void *kimage_map_segment(struct kimage *image, unsigned long addr, unsigned long size);
>> +extern void kimage_unmap_segment(void *buffer);
>>   #else /* !CONFIG_KEXEC_CORE */
>>   struct pt_regs;
>>   struct task_struct;
>> +struct kimage;
>>   static inline void __crash_kexec(struct pt_regs *regs) { }
>>   static inline void crash_kexec(struct pt_regs *regs) { }
>>   static inline int kexec_should_crash(struct task_struct *p) { return 0; }
>>   static inline int kexec_crash_loaded(void) { return 0; }
>> +static inline void *kimage_map_segment(struct kimage *image, unsigned long addr, unsigned long size)
>> +{ return NULL; }
>> +static inline void kimage_unmap_segment(void *buffer) { }
>>   #define kexec_in_progress false
>>   #endif /* CONFIG_KEXEC_CORE */
>>   
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index c0bdc1686154..a5e378e1dc7f 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -867,6 +867,60 @@ int kimage_load_segment(struct kimage *image,
>>   	return result;
>>   }
>>   
>> +void *kimage_map_segment(struct kimage *image,
>> +			 unsigned long addr, unsigned long size)
>> +{
>> +	unsigned long src_page_addr, dest_page_addr = 0;
>> +	unsigned long eaddr = addr + size;
>> +	kimage_entry_t *ptr, entry;
>> +	struct page **src_pages;
>> +	unsigned int npages;
>> +	void *vaddr = NULL;
>> +	int i;
>> +
>> +	/*
>> +	 * Collect the source pages and map them in a contiguous VA range.
>> +	 */
>> +	npages = PFN_UP(eaddr) - PFN_DOWN(addr);
>> +	src_pages = kmalloc_array(npages, sizeof(*src_pages), GFP_KERNEL);
>> +	if (!src_pages) {
>> +		pr_err("Could not allocate ima pages array.\n");
>> +		return NULL;
>> +	}
>> +
>> +	i = 0;
>> +	for_each_kimage_entry(image, ptr, entry) {
>> +		if (entry & IND_DESTINATION) {
>> +			dest_page_addr = entry & PAGE_MASK;
>> +		} else if (entry & IND_SOURCE) {
>> +			if (dest_page_addr >= addr && dest_page_addr < eaddr) {
>> +				src_page_addr = entry & PAGE_MASK;
>> +				src_pages[i++] =
>> +					virt_to_page(__va(src_page_addr));
>> +				if (i == npages)
>> +					break;
>> +				dest_page_addr += PAGE_SIZE;
>> +			}
>> +		}
>> +	}
>> +
>> +	/* Sanity check. */
>> +	WARN_ON(i < npages);
>> +
>> +	vaddr = vmap(src_pages, npages, VM_MAP, PAGE_KERNEL);
>> +	kfree(src_pages);
>> +
>> +	if (!vaddr)
>> +		pr_err("Could not map ima buffer.\n");
>> +
>> +	return vaddr;
>> +}
>> +
>> +void kimage_unmap_segment(void *segment_buffer)
>> +{
>> +	vunmap(segment_buffer);
>> +}
>> +
>>   struct kexec_load_limit {
>>   	/* Mutex protects the limit count. */
>>   	struct mutex mutex;
>> -- 
>> 2.43.0
>>