linux-kernel - Re: [PATCH] kho: fix out-of-bounds access of vmalloc chunk

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Message-ID: <aQje9CFnTymbkUlM@kernel.org>
Date: Mon, 3 Nov 2025 18:57:24 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
	Alexander Graf <graf@...zon.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	kexec@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kho: fix out-of-bounds access of vmalloc chunk

On Mon, Nov 03, 2025 at 12:01:57PM +0100, Pratyush Yadav wrote:
> The list of pages in a vmalloc chunk is NULL-terminated. So when looping
> through the pages in a vmalloc chunk, both kho_restore_vmalloc() and
> kho_vmalloc_unpreserve_chunk() rightly make sure to stop when
> encountering a NULL page. But when the chunk is full, the loops do not
> stop and go past the bounds of chunk->phys, resulting in out-of-bounds
> memory access, and possibly the restoration or unpreservation of an
> invalid page.
> 
> Fix this by making sure the processing of chunk stops at the end of the
> array.
> 
> Fixes: a667300bd53f2 ("kho: add support for preserving vmalloc allocations")
> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
> 
> Notes:
>     Commit 89a3ecca49ee8 ("kho: make sure page being restored is actually
>     from KHO") was quite helpful in catching this since kho_restore_page()
>     errored out due to missing magic number, instead of "restoring" a random
>     page and causing errors at other random places.
> 
>  kernel/kexec_handover.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index 76f0940fb4856..cc5aaa738bc50 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -869,7 +869,7 @@ static void kho_vmalloc_unpreserve_chunk(struct kho_vmalloc_chunk *chunk)
>  
>  	__kho_unpreserve(track, pfn, pfn + 1);
>  
> -	for (int i = 0; chunk->phys[i]; i++) {
> +	for (int i = 0; i < ARRAY_SIZE(chunk->phys) && chunk->phys[i]; i++) {
>  		pfn = PHYS_PFN(chunk->phys[i]);
>  		__kho_unpreserve(track, pfn, pfn + 1);
>  	}
> @@ -992,7 +992,7 @@ void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)
>  	while (chunk) {
>  		struct page *page;
>  
> -		for (int i = 0; chunk->phys[i]; i++) {
> +		for (int i = 0; i < ARRAY_SIZE(chunk->phys) && chunk->phys[i]; i++) {
>  			phys_addr_t phys = chunk->phys[i];
>  
>  			if (idx + contig_pages > total_pages)
> 
> base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.