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

[Jens Wiklander]

On Mon, Jun 14, 2021 at 02:06:46PM -0500, Tyler Hicks wrote:
> On 2021-06-14 10:27:15, Jens Wiklander wrote:
> > 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.
> 
> Yeah, I understand the issue with the naked bools. What about turning
> 'optee_disable_shm_cache(struct optee *optee, bool is_mapped)' into
> '__optee_disable_shm_cache(struct optee *optee, bool is_mapped)' and
> introducing these two wrappers:
> 
> /**
>  * optee_disable_shm_cache() - Disables caching of mapped shared memory
>  *                             allocations in OP-TEE
>  * @optee:     main service struct
>  */
> void optee_disable_shm_cache(struct optee *optee)
> {
>        return __optee_disable_shm_cache(optee, true);
> }
> 
> /**
>  * optee_disable_unmapped_shm_cache() - Disables caching of shared memory
>  *                                      allocations in OP-TEE which are not
>  *                                      currently mapped
>  * @optee:     main service struct
>  */
> void optee_disable_unmapped_shm_cache(struct optee *optee)
> {
>        return __optee_disable_shm_cache(optee, false);
> }
> 
> Existing callers of optee_disable_shm_cache() remain unchanged and we just add
> one caller of optee_disable_unmapped_shm_cache() with this patch.
> 

Sounds good.

Jens