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

Tyler Hicks
2021-06-14T19:06:54Z

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@linux.microsoft.com>
> > ---
> > 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.

Tyler

>
> /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
> >
>