linux-kernel - Re: [PATCH] nvmem: Enforce nvmem stride in the sysfs interface

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Date:   Fri, 29 May 2020 16:18:11 +0530
From:   "Ravi Kumar Bokka (Temp)" <rbokka@...eaurora.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     evgreen@...omium.org, dhavalp@...eaurora.org,
        mturney@...eaurora.org, sparate@...eaurora.org,
        rnayak@...eaurora.org, saiprakash.ranjan@...eaurora.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvmem: Enforce nvmem stride in the sysfs interface

Hi,

On 5/29/2020 5:23 AM, Douglas Anderson wrote:
> The 'struct nvmem_config' has a stride attribute that specifies the
> needed alignment for accesses into the nvmem.  This is used in
> nvmem_cell_info_to_nvmem_cell() but not in the sysfs read/write
> functions.  If the alignment is important in one place it's important
> everywhere, so let's add enforcement.
> 
> For now we'll consider it totally invalid to access with the wrong
> alignment.  We could relax this in the read case where we could just
> read some extra bytes and throw them away.  Relaxing it in the write
> case seems harder (and less safe?) since we'd have to read some data
> first and then write it back.  To keep it symmetric we'll just
> disallow it in both cases.
> 
> Reported-by: Ravi Kumar Bokka <rbokka@...eaurora.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>   drivers/nvmem/core.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 

I have reviewed and tested this patch.
Result: kernel crash resolved with unaligned offset.

Reviewed-by: Ravi Kumar Bokka <rbokka@...eaurora.org>
Tested-by: Ravi Kumar Bokka <rbokka@...eaurora.org>

> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 05c6ae4b0b97..1c0e7953f90d 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -111,6 +111,9 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
>   	if (pos >= nvmem->size)
>   		return 0;
>   
> +	if (!IS_ALIGNED(pos, nvmem->stride))
> +		return -EINVAL;
> +
>   	if (count < nvmem->word_size)
>   		return -EINVAL;
>   
> @@ -148,6 +151,9 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
>   	if (pos >= nvmem->size)
>   		return -EFBIG;
>   
> +	if (!IS_ALIGNED(pos, nvmem->stride))
> +		return -EINVAL;
> +
>   	if (count < nvmem->word_size)
>   		return -EINVAL;
>   
> 

Regards,
Ravi Kumar.B
-- 
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