Re: [PATCH] mm,ima,kexec: use memblock_free_late from ima_free_kexec_buffer

[Rob Herring <robh@kernel.org>]

On Thu, Jul 20, 2023 at 10:14:31AM -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")

Fixes: b69a2afd5afc ("x86/kexec: Carry forward IMA measurement log on kexec")

Acked-by: Rob Herring <robh@kernel.org>

(I'm assuming someone else is taking this)

> Cc: stable@kernel.org
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Suggested-by: Mike Rappoport <rppt@kernel.org>
> ---
>  arch/x86/kernel/setup.c | 8 ++------
>  drivers/of/kexec.c      | 3 ++-
>  2 files changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index fd975a4a5200..aa0df37c1fe7 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -359,15 +359,11 @@ static void __init add_early_ima_buffer(u64 phys_addr)
>  #if defined(CONFIG_HAVE_IMA_KEXEC) && !defined(CONFIG_OF_FLATTREE)
>  int __init ima_free_kexec_buffer(void)
>  {
> -	int rc;
> -
>  	if (!ima_kexec_buffer_size)
>  		return -ENOENT;
>  
> -	rc = memblock_phys_free(ima_kexec_buffer_phys,
> -				ima_kexec_buffer_size);
> -	if (rc)
> -		return rc;
> +	memblock_free_late(ima_kexec_buffer_phys,
> +			   ima_kexec_buffer_size);
>  
>  	ima_kexec_buffer_phys = 0;
>  	ima_kexec_buffer_size = 0;
> 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
>