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Date:   Tue, 16 Apr 2019 00:34:25 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     " Gustavo A. R. Silva " <gustavo@...eddedor.com>
Cc:     "Jaroslav Kysela" <perex@...ex.cz>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: isa/wavefront: Fix potential Spectre v1 vulnerabilities

On Mon, 15 Apr 2019 21:35:17 +0200,
 Gustavo A. R. Silva  wrote:
> 
> Hi all,
> 
> Friendly ping:
> 
> Who can take this?

All platforms that support ISA boards are so old and they don't suffer
from Spectre at all.


thanks,

Takashi


> 
> Thanks
> --
> Gustavo
> 
> On 3/26/19 1:32 PM, Gustavo A. R. Silva wrote:
> > header->number and i are indirectly controlled by user-space, hence leading
> > to a potential exploitation of the Spectre variant 1 vulnerability.
> > 
> > This issue was detected with the help of Smatch:
> > 
> > sound/isa/wavefront/wavefront_synth.c:792 wavefront_send_patch() warn: potential spectre issue 'dev->patch_status' [w] (local cap)
> > sound/isa/wavefront/wavefront_synth.c:819 wavefront_send_program() warn: potential spectre issue 'dev->prog_status' [w] (local cap)
> > sound/isa/wavefront/wavefront_synth.c:1197 wavefront_send_alias() warn: potential spectre issue 'dev->sample_status' [w]
> > sound/isa/wavefront/wavefront_synth.c:1248 wavefront_send_multisample() warn: potential spectre issue 'dev->sample_status' [w]
> > sound/isa/wavefront/wavefront_synth.c:1548 wavefront_synth_control() warn: potential spectre issue 'dev->sample_status' [r] (local cap)
> > 
> > Fix this by sanitizing header->number and i before using them to index
> > dev->patch_status, dev->prog_status, dev->sample_status.
> > 
> > Notice that given that speculation windows are large, the policy is
> > to kill the speculation on the first load and not worry if it can be
> > completed with a dependent load/store [1].
> > 
> > [1] https://lore.kernel.org/lkml/20180423164740.GY17484@dhcp22.suse.cz/
> > 
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> > ---
> >  sound/isa/wavefront/wavefront_synth.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/sound/isa/wavefront/wavefront_synth.c b/sound/isa/wavefront/wavefront_synth.c
> > index 0b1e4b34b299..a78e125dfdf9 100644
> > --- a/sound/isa/wavefront/wavefront_synth.c
> > +++ b/sound/isa/wavefront/wavefront_synth.c
> > @@ -31,6 +31,7 @@
> >  #include <linux/moduleparam.h>
> >  #include <linux/slab.h>
> >  #include <linux/module.h>
> > +#include <linux/nospec.h>
> >  #include <sound/core.h>
> >  #include <sound/snd_wavefront.h>
> >  #include <sound/initval.h>
> > @@ -788,6 +789,8 @@ wavefront_send_patch (snd_wavefront_t *dev, wavefront_patch_info *header)
> >  
> >  	if (header->number >= ARRAY_SIZE(dev->patch_status))
> >  		return -EINVAL;
> > +	header->number = array_index_nospec(header->number,
> > +					    ARRAY_SIZE(dev->patch_status));
> >  
> >  	dev->patch_status[header->number] |= WF_SLOT_FILLED;
> >  
> > @@ -815,6 +818,8 @@ wavefront_send_program (snd_wavefront_t *dev, wavefront_patch_info *header)
> >  
> >  	if (header->number >= ARRAY_SIZE(dev->prog_status))
> >  		return -EINVAL;
> > +	header->number = array_index_nospec(header->number,
> > +					    ARRAY_SIZE(dev->prog_status));
> >  
> >  	dev->prog_status[header->number] = WF_SLOT_USED;
> >  
> > @@ -1194,6 +1199,11 @@ wavefront_send_alias (snd_wavefront_t *dev, wavefront_patch_info *header)
> >  		return -EIO;
> >  	}
> >  
> > +	if (header->number >= ARRAY_SIZE(dev->sample_status))
> > +		return -EINVAL;
> > +	header->number = array_index_nospec(header->number,
> > +					    ARRAY_SIZE(dev->sample_status));
> > +
> >  	dev->sample_status[header->number] = (WF_SLOT_FILLED|WF_ST_ALIAS);
> >  
> >  	return (0);
> > @@ -1245,6 +1255,12 @@ wavefront_send_multisample (snd_wavefront_t *dev, wavefront_patch_info *header)
> >  		return -EIO;
> >  	}
> >  
> > +	if (header->number >= ARRAY_SIZE(dev->sample_status)) {
> > +		kfree(msample_hdr);
> > +		return -EINVAL;
> > +	}
> > +	header->number = array_index_nospec(header->number,
> > +					    ARRAY_SIZE(dev->sample_status));
> >  	dev->sample_status[header->number] = (WF_SLOT_FILLED|WF_ST_MULTISAMPLE);
> >  
> >  	kfree(msample_hdr);
> > @@ -1545,6 +1561,7 @@ wavefront_synth_control (snd_wavefront_card_t *acard,
> >  			wc->status = EINVAL;
> >  			return -EINVAL;
> >  		}
> > +		i = array_index_nospec(i, WF_MAX_SAMPLE);
> >  		wc->rbuf[0] = dev->sample_status[i];
> >  		wc->status = 0;
> >  		return 0;
> > 
> 

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