linux-kernel - Re: [PATCH] dmaengine: qcom: bam_dma: Avoid accessing BAM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <jzb4ccukx6u64ewtwyhik2ezhrmawc2in5eyktt5dnm2orr3jh@bwtgerefsukb>
Date: Tue, 11 Feb 2025 20:43:12 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: Bjorn Andersson <bjorn.andersson@....qualcomm.com>, 
	Vinod Koul <vkoul@...nel.org>, Md Sadre Alam <quic_mdalam@...cinc.com>, 
	linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Georgi Djakov <djakov@...nel.org>
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Avoid accessing BAM_REVISION
 on remote BAM

On Mon, Feb 10, 2025 at 09:44:30AM +0100, Stephan Gerhold wrote:
> On Fri, Feb 07, 2025 at 12:17:33PM -0800, Bjorn Andersson wrote:
> > Commit '57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing
> > unavailable register")' made this read unconditional, in order to
> > identify if the instance is BAM-NDP or BAM-Lite.
> > But the BAM_REVISION register is not accessible on remotely managed BAM
> > instances and attempts to access it causes the system to crash.
> > 
> > Move the access back to be conditional and expand the checks that was
> > introduced to restore the old behavior when no revision information is
> > available.
> > 
> > Fixes: 57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing unavailable register")
> > Reported-by: Georgi Djakov <djakov@...nel.org>
> > Closes: https://lore.kernel.org/lkml/9ef3daa8-cdb1-49f2-8d19-a72d6210ff3a@kernel.org/
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@....qualcomm.com>
> 
> This patch fixes the most critical regression (the bus hang), but the
> in_range(..., BAM_NDP) checks are also wrong. They do not consider the
> plain "BAM" type where the register is apparently also available. The
> check should be !in_range(..., BAM_LITE) instead to fix this.
> 

Sorry, I must have not paid sufficient attention while browsing the
replies; and just tried to restore the one case I thought the author
didn't consider...

Thanks for staying on top of it. Revert makes total sense.

Regards,
Bjorn

> I mentioned this twice to Md Sadre Alam [1, 2], but a fix was
> unfortunately never sent for that part of the regression.
> 
> I think we should take Caleb's patch and revert the entire patch for the
> 6.14 cycle. There are several incorrect assumptions in the original
> patch, it will be easier to review a fixed version with the full diff,
> rather than looking at incremental fixups.
> 
> On a somewhat related note, I'm working on a patch series for bam_dma to
> clean up the handling of remotely controlled BAMs. It will make it more
> clear when it's safe to access BAM registers and when not, and should
> allow reading the revision also for remotely controlled BAMs. This would
> avoid the need for all these if (!bdev->bam_revision) checks.
> 
> Thanks,
> Stephan
> 
> [1]: https://lore.kernel.org/linux-arm-msm/Z4D2jQNNW94qGIlv@linaro.org/
> [2]: https://lore.kernel.org/linux-arm-msm/Z4_U19_QyH2RJvKW@linaro.org/
> 
> > ---
> >  drivers/dma/qcom/bam_dma.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> > index c14557efd577..d42d913492a8 100644
> > --- a/drivers/dma/qcom/bam_dma.c
> > +++ b/drivers/dma/qcom/bam_dma.c
> > @@ -445,8 +445,8 @@ static void bam_reset(struct bam_device *bdev)
> >  	writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
> >  
> >  	/* set descriptor threshold, start with 4 bytes */
> > -	if (in_range(bdev->bam_revision, BAM_NDP_REVISION_START,
> > -		     BAM_NDP_REVISION_END))
> > +	if (!bdev->bam_revision ||
> > +	    in_range(bdev->bam_revision, BAM_NDP_REVISION_START, BAM_NDP_REVISION_END))
> >  		writel_relaxed(DEFAULT_CNT_THRSHLD,
> >  			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
> >  
> > @@ -1006,8 +1006,8 @@ static void bam_apply_new_config(struct bam_chan *bchan,
> >  			maxburst = bchan->slave.src_maxburst;
> >  		else
> >  			maxburst = bchan->slave.dst_maxburst;
> > -		if (in_range(bdev->bam_revision, BAM_NDP_REVISION_START,
> > -			     BAM_NDP_REVISION_END))
> > +		if (!bdev->bam_revision ||
> > +		    in_range(bdev->bam_revision, BAM_NDP_REVISION_START, BAM_NDP_REVISION_END))
> >  			writel_relaxed(maxburst,
> >  				       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
> >  	}
> > @@ -1199,11 +1199,12 @@ static int bam_init(struct bam_device *bdev)
> >  	u32 val;
> >  
> >  	/* read revision and configuration information */
> > -	val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
> > -	if (!bdev->num_ees)
> > +	if (!bdev->num_ees) {
> > +		val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
> >  		bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK;
> >  
> > -	bdev->bam_revision = val & REVISION_MASK;
> > +		bdev->bam_revision = val & REVISION_MASK;
> > +	}
> >  
> >  	/* check that configured EE is within range */
> >  	if (bdev->ee >= bdev->num_ees)
> > 
> > ---
> > base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
> > change-id: 20250207-bam-read-fix-2b31297d3fa1
> > 
> > Best regards,
> > -- 
> > Bjorn Andersson <bjorn.andersson@....qualcomm.com>
> > 
>