Re: [PATCH 1/3 v2] kexec: modify the meaning of the end parameter in kimage_is_destination_range()

From: Baoquan He <bhe@redhat.com>
To: Yuntao Wang <ytcoode@gmail.com>
Cc: akpm@linux-foundation.org, bp@alien8.de, corbet@lwn.net,
	dave.hansen@linux.intel.com, ebiederm@xmission.com,
	hpa@zytor.com, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, mingo@redhat.com,
	tglx@linutronix.de, x86@kernel.org
Subject: Re: [PATCH 1/3 v2] kexec: modify the meaning of the end parameter in kimage_is_destination_range()
Date: Sat, 16 Dec 2023 17:29:35 +0800	[thread overview]
Message-ID: <ZX1t/4Reai6HdoJf@MiWiFi-R3L-srv> (raw)
In-Reply-To: <20231216041833.220466-1-ytcoode@gmail.com>

On 12/16/23 at 12:18pm, Yuntao Wang wrote:
> The end parameter received by kimage_is_destination_range() should be the
> last valid byte address of the target memory segment plus 1. However, in
> the locate_mem_hole_bottom_up() and locate_mem_hole_top_down() functions,
> the corresponding value passed to kimage_is_destination_range() is the last
> valid byte address of the target memory segment, which is 1 less.
> 
> There are two ways to fix this bug. We can either correct the logic of the
> locate_mem_hole_bottom_up() and locate_mem_hole_top_down() functions, or we
> can fix kimage_is_destination_range() by making the end parameter represent
> the last valid byte address of the target memory segment. Here, we choose
> the second approach.
> 
> Due to the modification to kimage_is_destination_range(), we also need to
> adjust its callers, such as kimage_alloc_normal_control_pages() and
> kimage_alloc_page().
> 
> Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
> ---
> v1->v2:
>   Fix this issue using the approach suggested by Eric and Baoquan.
> 
>   As this patch is independent of the other patches in this series, I sent
>   out the v2 patch separately. If it's inconvenient for anyone, I can
>   resend the entire series again.
> 
>  kernel/kexec_core.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index be5642a4ec49..5991b3ae072c 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -276,8 +276,8 @@ int kimage_is_destination_range(struct kimage *image,
>  		unsigned long mstart, mend;
>  
>  		mstart = image->segment[i].mem;
> -		mend = mstart + image->segment[i].memsz;
> -		if ((end > mstart) && (start < mend))
> +		mend = mstart + image->segment[i].memsz - 1;
> +		if ((end >= mstart) && (start <= mend))
>  			return 1;
>  	}
>  
> @@ -372,7 +372,7 @@ static struct page *kimage_alloc_normal_control_pages(struct kimage *image,
>  		addr  = pfn << PAGE_SHIFT;
>  		eaddr = epfn << PAGE_SHIFT;

  		eaddr = epfn << PAGE_SHIFT - 1;

The overall looks good to me, one tiny concern is I would like to
have 'eaddr' changed as above if a specific local variable has been
defined.

>  		if ((epfn >= (KEXEC_CONTROL_MEMORY_LIMIT >> PAGE_SHIFT)) ||
> -			      kimage_is_destination_range(image, addr, eaddr)) {
> +			      kimage_is_destination_range(image, addr, eaddr - 1)) {

Then we have:

 +			      kimage_is_destination_range(image, addr, eaddr)) {

>  			list_add(&pages->lru, &extra_pages);
>  			pages = NULL;
>  		}
> @@ -716,7 +716,7 @@ static struct page *kimage_alloc_page(struct kimage *image,
>  
>  		/* If the page is not a destination page use it */
>  		if (!kimage_is_destination_range(image, addr,
> -						  addr + PAGE_SIZE))
> +						  addr + PAGE_SIZE - 1))
>  			break;
>  
>  		/*
> -- 
> 2.43.0
> 

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