linux-kernel - Re: [PATCH] powerpc: check previous kernel's ima-kexec-buffer against memory bounds

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Message-ID: <83e757fe-5269-693b-ee8c-c5186ea5fcdd@linux.microsoft.com>
Date:   Wed, 18 May 2022 13:30:49 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Vaibhav Jain <vaibhav@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Frank Rowand <frowand.list@...il.com>,
        Prakhar Srivastava <prsriva@...ux.microsoft.com>,
        Rob Herring <robh@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>, nramas@...ux.microsoft.com
Subject: Re: [PATCH] powerpc: check previous kernel's ima-kexec-buffer against
 memory bounds

Hi Vaibhav,

On 5/18/2022 1:05 PM, Vaibhav Jain wrote:
> Presently ima_get_kexec_buffer() doesn't check if the previous kernel's
> ima-kexec-buffer lies outside the addressable memory range. This can result
> in a kernel panic if the new kernel is booted with 'mem=X' arg and the
> ima-kexec-buffer was allocated beyond that range by the previous kernel.

Thanks for providing this patch.

> Fix this issue by checking returned address/size of previous kernel's
> ima-kexec-buffer against memblock's memory bounds.
> 
> Fixes: fee3ff99bc67("powerpc: Move arch independent ima kexec functions to
> drivers/of/kexec.c")
> 
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: Prakhar Srivastava <prsriva@...ux.microsoft.com>
> Cc: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
> Cc: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> Cc: Rob Herring <robh@...nel.org>
> Signed-off-by: Vaibhav Jain <vaibhav@...ux.ibm.com>
> ---
>   drivers/of/kexec.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index b9bd1cff1793..c73007eda52d 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -140,6 +140,13 @@ int ima_get_kexec_buffer(void **addr, size_t *size)
>   	if (ret)
>   		return ret;
>   
> +	/* if the ima-kexec-buffer goes beyond the addressable memory */
> +	if (!memblock_is_region_memory(tmp_addr, tmp_size)) {
> +		pr_warn("IMA buffer at 0x%lx, size = 0x%zx beyond memory\n",
> +			tmp_addr, tmp_size);
> +		return -EINVAL;
> +	}
> +
Reviewed-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>

>   	*addr = __va(tmp_addr);
>   	*size = tmp_size;
>