Re: [PATCH v2] platform/x86/amd: pmf: Use device managed allocations

[Dan Carpenter <dan.carpenter@linaro.org>]

On Thu, May 08, 2025 at 02:33:54PM -0500, Mario Limonciello wrote:
> On 5/7/2025 4:44 AM, Ilpo Järvinen wrote:
> > On Tue, 6 May 2025, Mario Limonciello wrote:
> > 
> > > From: Mario Limonciello <mario.limonciello@amd.com>
> > > 
> > > If setting up smart PC fails for any reason then this can lead to
> > > a double free when unloading amd-pmf.  This is because dev->buf was
> > > freed but never set to NULL and is again freed in amd_pmf_remove().
> > > 
> > > To avoid subtle allocation bugs in failures leading to a double free
> > > change all allocations into device managed allocations.
> > > 
> > > Fixes: 5b1122fc4995f ("platform/x86/amd/pmf: fix cleanup in amd_pmf_init_smart_pc()")
> > > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> > > ---
> > > v1->v2:
> > >   * Correct commit message with correct offending function root cause
> > >   * Switch to device managed allocations.
> > > 
> > >   drivers/platform/x86/amd/pmf/core.c   |  3 +--
> > >   drivers/platform/x86/amd/pmf/tee-if.c | 30 ++++++++-------------------
> > >   2 files changed, 10 insertions(+), 23 deletions(-)
> > > 
> > > diff --git a/drivers/platform/x86/amd/pmf/core.c b/drivers/platform/x86/amd/pmf/core.c
> > > index 96821101ec773..395c011e837f1 100644
> > > --- a/drivers/platform/x86/amd/pmf/core.c
> > > +++ b/drivers/platform/x86/amd/pmf/core.c
> > > @@ -280,7 +280,7 @@ int amd_pmf_set_dram_addr(struct amd_pmf_dev *dev, bool alloc_buffer)
> > >   			dev_err(dev->dev, "Invalid CPU id: 0x%x", dev->cpu_id);
> > >   		}
> > > -		dev->buf = kzalloc(dev->mtable_size, GFP_KERNEL);
> > > +		dev->buf = devm_kzalloc(dev->dev, dev->mtable_size, GFP_KERNEL);
> > >   		if (!dev->buf)
> > >   			return -ENOMEM;
> > >   	}
> > > @@ -493,7 +493,6 @@ static void amd_pmf_remove(struct platform_device *pdev)
> > >   	mutex_destroy(&dev->lock);
> > >   	mutex_destroy(&dev->update_mutex);
> > >   	mutex_destroy(&dev->cb_mutex);
> > > -	kfree(dev->buf);
> > >   }
> > >   static const struct attribute_group *amd_pmf_driver_groups[] = {
> > > diff --git a/drivers/platform/x86/amd/pmf/tee-if.c b/drivers/platform/x86/amd/pmf/tee-if.c
> > > index d3bd12ad036ae..50c082a78cd9e 100644
> > > --- a/drivers/platform/x86/amd/pmf/tee-if.c
> > > +++ b/drivers/platform/x86/amd/pmf/tee-if.c
> > > @@ -532,13 +532,13 @@ int amd_pmf_init_smart_pc(struct amd_pmf_dev *dev)
> > >   	dev->policy_base = devm_ioremap_resource(dev->dev, dev->res);
> > >   	if (IS_ERR(dev->policy_base)) {
> > >   		ret = PTR_ERR(dev->policy_base);
> > > -		goto err_free_dram_buf;
> > > +		goto err_cancel_work;
> > >   	}
> > > -	dev->policy_buf = kzalloc(dev->policy_sz, GFP_KERNEL);
> > > +	dev->policy_buf = devm_kzalloc(dev->dev, dev->policy_sz, GFP_KERNEL);
> > 
> > Hi Mario,
> > 
> > Isn't ->policy_buf freed and another allocated in amd_pmf_get_pb_data()
> > and this patch lacks any changes around there?? That switch of the buffer
> > has been the reason why I've not suggested using devm_*() for earlier for
> > it.
> > 
> > Please check all related code to the pointers you're changing if there
> > are other similar traps you have not taken into account.
> 
> Ah, thanks I thought I caught them all but missed that instance.
> 
> A few options that come to mind:
> 1) instead make the very first allocation POLICY_BUF_MAX_SZ, and then never
> reallocate for the life of the driver.
> 2) Don't allow sideloading a bigger policy than the original one in the
> firmware.
> 3) Don't switch all 3 to device managed like this patch, just switch the two
> that can and fix the one broken one causing a double free.
> 4) Switch the case you pointed out to use devm_kfree() and re-allocate at
> that time.
> 
> Anyone with a preference?  I lean upon option 4.
> 

I feel like Option 3 is the worst...

I didn't have a problem with your v1 patch if we had fix the
amd_pmf_tee_deinit() bug as well and probably deleted the
second kfree().

I think there is a race with the debugfs sideloader, but it's
debugfs and root only so if you hit that race, then you deserve
it.

regards,
dan carpenter