linux-kernel - Re: [PATCH v4] soc: qcom: mdt_loader: Add Upperbounds check for program header access

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Date: Sat, 16 Mar 2024 12:17:20 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Auditya Bhattaram <quic_audityab@...cinc.com>
Cc: konrad.dybcio@...aro.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v4] soc: qcom: mdt_loader: Add Upperbounds check for
 program header access

On Wed, Feb 14, 2024 at 11:27:01AM +0530, Auditya Bhattaram wrote:
> 
> 
> On 2/14/2024 11:12 AM, Bjorn Andersson wrote:
> > On Tue, Feb 13, 2024 at 01:30:10PM +0530, Auditya Bhattaram wrote:
> > > hash_index is evaluated by looping phdrs till QCOM_MDT_TYPE_HASH
> > > is found. Add an upperbound check to phdrs to access within elf size.
> > > 
> > 
> > How is this compatible with what is being observed on SM8450 and
> > implemented in commit 8bd42e2341a7 ("soc: qcom: mdt_loader: Allow hash
> > segment to be split out"?
> > 
> > Regards,
> > Bjorn
> > 
> 
> Calculating hash_index is introduced with this commit 8bd42e2341a7 ("soc:
> qcom: mdt_loader: Allow hash segment to be split out"
> 
>     for (i = 1; i < ehdr->e_phnum; i++) {
>  	if ((phdrs[i].p_flags & QCOM_MDT_TYPE_MASK) ...
> 
> I'm trying to add an upper bound for this access "phdrs[i]"
> 

Ahh, sorry, you're of course correct. I think I would have preferred a
more obvious check of offset >= fw->size though...

That said, this code used to sit behind rproc_elf_sanity_check(), but
that seem to have been lost in the refactorings. As such, your patch is
incomplete and we should reintroduce a whole bunch of these sanity
checks!

Regards,
Bjorn

> > > Fixes: 64fb5eb87d58 ("soc: qcom: mdt_loader: Allow hash to reside in any segment")
> > > Cc: <stable@...r.kernel.org>
> > > Signed-off-by: Auditya Bhattaram <quic_audityab@...cinc.com>
> > > Acked-by: Mukesh Ojha <quic_mojha@...cinc.com>
> > > ---
> > > Changes in v4:
> > >   - Added additional prints incase of Invalid access.
> > > Link to v3 https://lore.kernel.org/stable/1c91c653-cebe-4407-bdd6-cfc73b64c0fb@quicinc.com
> > > Link to v2 https://lore.kernel.org/linux-arm-msm/9773d189-c896-d5c5-804c-e086c24987b4@quicinc.com/T/#t
> > > Link to v1 https://lore.kernel.org/linux-arm-msm/5d7a3b97-d840-4863-91a0-32c1d8e7532f@linaro.org/T/#t
> > > ---
> > >   drivers/soc/qcom/mdt_loader.c | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/drivers/soc/qcom/mdt_loader.c b/drivers/soc/qcom/mdt_loader.c
> > > index 6f177e46fa0f..1a79a7bba468 100644
> > > --- a/drivers/soc/qcom/mdt_loader.c
> > > +++ b/drivers/soc/qcom/mdt_loader.c
> > > @@ -145,6 +143,13 @@ void *qcom_mdt_read_metadata(const struct firmware *fw, size_t *data_len,
> > >   	if (phdrs[0].p_type == PT_LOAD)
> > >   		return ERR_PTR(-EINVAL);
> > > 
> > > +	if (((size_t)(phdrs + ehdr->e_phnum)) > ((size_t)ehdr + fw->size)) {
> > > +		dev_err(dev,
> > > +			"Invalid phdrs access for fw: %s, e_phnum: %u, fw->size: %zu\n",
> > > +			fw_name, ehdr->e_phnum, fw->size);
> > > +		return ERR_PTR(-EINVAL);
> > > +	}
> > > +
> > >   	for (i = 1; i < ehdr->e_phnum; i++) {
> > >   		if ((phdrs[i].p_flags & QCOM_MDT_TYPE_MASK) == QCOM_MDT_TYPE_HASH) {
> > >   			hash_segment = i;
> > > --
> > > 2.17.1
> > >