Re: [PATCH v4 4/8] optee: Clear stale cache entries during initialization

[Jens Wiklander]

On Thu, Jun 10, 2021 at 04:09:09PM -0500, Tyler Hicks wrote:
> The shm cache could contain invalid addresses if
> optee_disable_shm_cache() was not called from the .shutdown hook of the
> previous kernel before a kexec. These addresses could be unmapped or
> they could point to mapped but unintended locations in memory.
> 
> Clear the shared memory cache, while being careful to not translate the
> addresses returned from OPTEE_SMC_DISABLE_SHM_CACHE, during driver
> initialization. Once all pre-cache shm objects are removed, proceed with
> enabling the cache so that we know that we can handle cached shm objects
> with confidence later in the .shutdown hook.
> 
> Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/tee/optee/call.c          | 11 ++++++++++-
>  drivers/tee/optee/core.c          | 13 +++++++++++--
>  drivers/tee/optee/optee_private.h |  2 +-
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c
> index 6e6eb836e9b6..5dcba6105ed7 100644
> --- a/drivers/tee/optee/call.c
> +++ b/drivers/tee/optee/call.c
> @@ -419,8 +419,10 @@ void optee_enable_shm_cache(struct optee *optee)
>   * optee_disable_shm_cache() - Disables caching of some shared memory allocation
>   *			      in OP-TEE
>   * @optee:	main service struct
> + * @is_mapped:	true if the cached shared memory addresses were mapped by this
> + *		kernel, are safe to dereference, and should be freed
>   */
> -void optee_disable_shm_cache(struct optee *optee)
> +void optee_disable_shm_cache(struct optee *optee, bool is_mapped)
>  {
>  	struct optee_call_waiter w;
>  
> @@ -439,6 +441,13 @@ void optee_disable_shm_cache(struct optee *optee)
>  		if (res.result.status == OPTEE_SMC_RETURN_OK) {
>  			struct tee_shm *shm;
>  
> +			/*
> +			 * Shared memory references that were not mapped by
> +			 * this kernel must be ignored to prevent a crash.
> +			 */
> +			if (!is_mapped)
> +				continue;
> +
>  			shm = reg_pair_to_ptr(res.result.shm_upper32,
>  					      res.result.shm_lower32);
>  			tee_shm_free(shm);
> diff --git a/drivers/tee/optee/core.c b/drivers/tee/optee/core.c
> index 0987074d7ed0..6974e1104bd4 100644
> --- a/drivers/tee/optee/core.c
> +++ b/drivers/tee/optee/core.c
> @@ -589,7 +589,7 @@ static int optee_remove(struct platform_device *pdev)
>  	 * reference counters and also avoid wild pointers in secure world
>  	 * into the old shared memory range.
>  	 */
> -	optee_disable_shm_cache(optee);
> +	optee_disable_shm_cache(optee, true);

Naked "true" or "false" parameters are normally not very descriptive.
Would it make sense to write this as:
optee_disable_shm_cache(optee, true /*is_mapped*/);
instead (same for the other call sites in this patch)? That way it would
be easier to see what it is that is true or false.

/Jens

>  
>  	/*
>  	 * The two devices have to be unregistered before we can free the
> @@ -619,7 +619,7 @@ static int optee_remove(struct platform_device *pdev)
>   */
>  static void optee_shutdown(struct platform_device *pdev)
>  {
> -	optee_disable_shm_cache(platform_get_drvdata(pdev));
> +	optee_disable_shm_cache(platform_get_drvdata(pdev), true);
>  }
>  
>  static int optee_probe(struct platform_device *pdev)
> @@ -716,6 +716,15 @@ static int optee_probe(struct platform_device *pdev)
>  	optee->memremaped_shm = memremaped_shm;
>  	optee->pool = pool;
>  
> +	/*
> +	 * Ensure that there are no pre-existing shm objects before enabling
> +	 * the shm cache so that there's no chance of receiving an invalid
> +	 * address during shutdown. This could occur, for example, if we're
> +	 * kexec booting from an older kernel that did not properly cleanup the
> +	 * shm cache.
> +	 */
> +	optee_disable_shm_cache(optee, false);
> +
>  	optee_enable_shm_cache(optee);
>  
>  	if (optee->sec_caps & OPTEE_SMC_SEC_CAP_DYNAMIC_SHM)
> diff --git a/drivers/tee/optee/optee_private.h b/drivers/tee/optee/optee_private.h
> index e25b216a14ef..16d8c82213e7 100644
> --- a/drivers/tee/optee/optee_private.h
> +++ b/drivers/tee/optee/optee_private.h
> @@ -158,7 +158,7 @@ int optee_invoke_func(struct tee_context *ctx, struct tee_ioctl_invoke_arg *arg,
>  int optee_cancel_req(struct tee_context *ctx, u32 cancel_id, u32 session);
>  
>  void optee_enable_shm_cache(struct optee *optee);
> -void optee_disable_shm_cache(struct optee *optee);
> +void optee_disable_shm_cache(struct optee *optee, bool is_mapped);
>  
>  int optee_shm_register(struct tee_context *ctx, struct tee_shm *shm,
>  		       struct page **pages, size_t num_pages,
> -- 
> 2.25.1
>