linux-kernel - Re: [PATCH] mm,ima,kexec,of: use memblock_free_late from ima_free_kexec

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Message-ID: <20230818170929.GA151785-robh@kernel.org>
Date:   Fri, 18 Aug 2023 12:09:29 -0500
From:   Rob Herring <robh@...nel.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH] mm,ima,kexec,of: use memblock_free_late from
 ima_free_kexec_buffer

On Thu, Aug 17, 2023 at 01:57:59PM -0400, Rik van Riel wrote:
> The code calling ima_free_kexec_buffer runs long after the memblock
> allocator has already been torn down, potentially resulting in a use
> after free in memblock_isolate_range.
> 
> With KASAN or KFENCE, this use after free will result in a BUG
> from the idle task, and a subsequent kernel panic.
> 
> Switch ima_free_kexec_buffer over to memblock_free_late to avoid
> that issue.
> 
> Fixes: fee3ff99bc67 ("powerpc: Move arch independent ima kexec functions to
> drivers/of/kexec.c")

Didn't powerpc have the same issue before this commit? The move changed 
memblock_free() to memblock_phys_free(), but otherwise the code was the 
same. But wait, the old code looks broken as it reads a phys addr from 
DT and passes that to memblock_free() which wants a virt addr. Probably 
should have fixed that before moving things. I guess the Fixes here is 
right and powerpc needs a different backport for before commit 
fee3ff99bc67 if they care.

> Cc: stable@...nel.org
> Signed-off-by: Rik van Riel <riel@...riel.com>
> Suggested-by: Mike Rappoport <rppt@...nel.org>
> ---
>  drivers/of/kexec.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index f26d2ba8a371..68278340cecf 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -184,7 +184,8 @@ int __init ima_free_kexec_buffer(void)
>  	if (ret)
>  		return ret;
>  
> -	return memblock_phys_free(addr, size);
> +	memblock_free_late(addr, size);
> +	return 0;
>  }
>  #endif
>  
> -- 
> 2.41.0
>