linux-kernel - Re: [PATCH 1/2] soc: qcom: smem: introduce qcom_smem_validate

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Message-ID: <CAOdFzcjzzymRxqoeF+FDidDo1aa-fNzV-3kERoV7HRW7RpQ1kA@mail.gmail.com>
Date: Thu, 30 Oct 2025 17:40:51 -0700
From: Christopher Lew <christopher.lew@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>,
        Chris Lew <chris.lew@....qualcomm.com>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] soc: qcom: smem: introduce qcom_smem_validate_item API

On Thu, Oct 30, 2025 at 9:48 AM Bjorn Andersson <andersson@...nel.org> wrote:
>
> On Thu, Oct 30, 2025 at 03:07:48PM +0530, Kathiravan Thirumoorthy wrote:
> > When a SMEM item is allocated or retrieved, sanity check on the SMEM item
> > is performed and backtrace is printed if the SMEM item is invalid.
> >
>
> That sounds overly defensive...
>

Discussed with Bjorn a bit offline and we couldn't come up with a
really good reason to keep the WARN_ON() check.
Dropping WARN_ON() and returning an error back from qcom_smem_get()
that clients can act on should suffice.

> > Image version table in SMEM contains version details for the first 32
> > images. Beyond that, another SMEM item 667 is being used, which may not
> > be defined in all the platforms. So directly retrieving the SMEM item 667,
> > throws the warning as invalid item number.
> >
> > To handle such cases, introduce a new API to validate the SMEM item before
> > processing it. While at it, make use of this API in the SMEM driver where
> > possible.
> >
> > Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
> > ---
> >  drivers/soc/qcom/smem.c       | 16 ++++++++++++++--
> >  include/linux/soc/qcom/smem.h |  1 +
> >  2 files changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/soc/qcom/smem.c b/drivers/soc/qcom/smem.c
> > index c4c45f15dca4fb14f97df4ad494c1189e4f098bd..8a0a832f1e9915b2177a0fe08298ffe8a779e516 100644
> > --- a/drivers/soc/qcom/smem.c
> > +++ b/drivers/soc/qcom/smem.c
> > @@ -396,6 +396,18 @@ bool qcom_smem_is_available(void)
> >  }
> >  EXPORT_SYMBOL_GPL(qcom_smem_is_available);
> >
> > +/**
> > + * qcom_smem_validate_item() - Check if SMEM item is within the limit
>
> If nothing else, this contradicts the comment by SMEM_ITEM_COUNT.
>
> > + * @item:    SMEM item to validate
> > + *
> > + * Return: true if SMEM item is valid, false otherwise.
> > + */
> > +bool qcom_smem_validate_item(unsigned item)
> > +{
> > +     return item < __smem->item_count;
> > +}
> > +EXPORT_SYMBOL_GPL(qcom_smem_validate_item);
> > +
> >  static int qcom_smem_alloc_private(struct qcom_smem *smem,
> >                                  struct smem_partition *part,
> >                                  unsigned item,
> > @@ -517,7 +529,7 @@ int qcom_smem_alloc(unsigned host, unsigned item, size_t size)
> >               return -EINVAL;
> >       }
> >
> > -     if (WARN_ON(item >= __smem->item_count))
> > +     if (WARN_ON(!qcom_smem_validate_item(item)))
>
> When we're using a version 11 (global heap, with toc indexed by the item
> number) the SMEM_ITEM_COUNT actually matters, but when we use version 12
> the items are stored in linked lists, so the only limit I can see is
> that the item needs to be max 16 bit.
>
> I think we should push this check down to qcom_smem_alloc_global().
>
> And have a sanity check for item in qcom_smem_alloc_private() and
> qcom_smem_get_private() to avoid truncation errors.
>

For alloc, I think we should adhere to the platform defined max
item_count. I'm not sure if the remote hosts validate the entries
against item_count while they are iterating through the items during
their implementation of qcom_smem_get().

> >               return -EINVAL;
> >
> >       ret = hwspin_lock_timeout_irqsave(__smem->hwlock,
> > @@ -690,7 +702,7 @@ void *qcom_smem_get(unsigned host, unsigned item, size_t *size)
> >       if (!__smem)
> >               return ptr;
> >
> > -     if (WARN_ON(item >= __smem->item_count))
> > +     if (WARN_ON(!qcom_smem_validate_item(item)))
>
> I think we should push this check down to qcom_smem_get_global()
>
> I guess we'd still hit your problem on version 11 platforms if we keep
> the WARN_ON(), but I don't know why that's reason for throwing a splat
> in the log. Let's drop the WARN_ON() as well.
>

I think it's worth keeping the item_count check here because it acts
as a quick short circuit out of the search loop for absurd values in
qcom_smem_get_private().

Thanks,
Chris

> >               return ERR_PTR(-EINVAL);
> >
> >       if (host < SMEM_HOST_COUNT && __smem->partitions[host].virt_base) {
> > diff --git a/include/linux/soc/qcom/smem.h b/include/linux/soc/qcom/smem.h
> > index f946e3beca215548ac56dbf779138d05479712f5..05891532d530a25747afb8dc96ad4ba668598197 100644
> > --- a/include/linux/soc/qcom/smem.h
> > +++ b/include/linux/soc/qcom/smem.h
> > @@ -5,6 +5,7 @@
> >  #define QCOM_SMEM_HOST_ANY -1
> >
> >  bool qcom_smem_is_available(void);
> > +bool qcom_smem_validate_item(unsigned item);
>
> This makes the API clunky for no real reason, let's avoid that.
>
>
> Adding Chris, in case I'm overlooking something here.
>
> Regards,
> Bjorn
>
> >  int qcom_smem_alloc(unsigned host, unsigned item, size_t size);
> >  void *qcom_smem_get(unsigned host, unsigned item, size_t *size);
> >
> >
> > --
> > 2.34.1
> >