linux-kernel - Re: [PATCH] memory: mtk-smi: Fix a null dereference for the ostd

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Date:   Mon, 1 Nov 2021 14:09:14 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
CC:     Krzysztof Kozlowski <krzk@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Tomasz Figa" <tfiga@...omium.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <youlin.pei@...iatek.com>,
        <anan.sun@...iatek.com>, <yi.kuo@...iatek.com>,
        <anthony.huang@...iatek.com>, Ikjoon Jang <ikjn@...omium.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>
Subject: Re: [PATCH] memory: mtk-smi: Fix a null dereference for the ostd

On Fri, 2021-10-29 at 19:35 +0200, Krzysztof Kozlowski wrote:
> On 28/10/2021 07:50, Yong Wu wrote:
> > We add the ostd setting for mt8195. It introduces a abort for the
> > previous SoC which doesn't have ostd setting. This is the log:
> > 
> > Unable to handle kernel NULL pointer dereference at virtual address
> > 0000000000000080
> > ...
> > pc : mtk_smi_larb_config_port_gen2_general+0x64/0x130
> > lr : mtk_smi_larb_resume+0x54/0x98
> > ...
> > Call trace:
> >  mtk_smi_larb_config_port_gen2_general+0x64/0x130
> >  pm_generic_runtime_resume+0x2c/0x48
> >  __genpd_runtime_resume+0x30/0xa8
> >  genpd_runtime_resume+0x94/0x2c8
> >  __rpm_callback+0x44/0x150
> >  rpm_callback+0x6c/0x78
> >  rpm_resume+0x310/0x558
> >  __pm_runtime_resume+0x3c/0x88
> > 
> > In the code: larbostd = larb->larb_gen->ostd[larb->larbid],
> > if "larb->larb_gen->ostd" is null, the "larbostd" is the offset, it
> > is
> > also a valid value, thus, use the larb->larb_gen->ostd as the
> > condition
> > inside the "for" loop.
> 
> You need to write more clearly, what you are fixing here.
> 
> > 
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> > Hi Krzysztof,
> > Could you help review and conside this as a fix for the mt8195
> > patchset?
> > The mt8195 patchset are not in mainline, thus, I don't know its
> > sha-id,
> > and don't add Fixes tag.
> > Thanks
> > ---
> >  drivers/memory/mtk-smi.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/memory/mtk-smi.c b/drivers/memory/mtk-smi.c
> > index b883dcc0bbfa..0262a59a2d6e 100644
> > --- a/drivers/memory/mtk-smi.c
> > +++ b/drivers/memory/mtk-smi.c
> > @@ -257,7 +257,7 @@ static void
> > mtk_smi_larb_config_port_gen2_general(struct device *dev)
> >  	if (MTK_SMI_CAPS(flags_general, MTK_SMI_FLAG_SW_FLAG))
> >  		writel_relaxed(SMI_LARB_SW_FLAG_1, larb->base +
> > SMI_LARB_SW_FLAG);
> >  
> > -	for (i = 0; i < SMI_LARB_PORT_NR_MAX && larbostd &&
> > !!larbostd[i]; i++)
> > +	for (i = 0; i < SMI_LARB_PORT_NR_MAX && larb->larb_gen->ostd &&
> > !!larbostd[i]; i++)
> >  		writel_relaxed(larbostd[i], larb->base +
> > SMI_LARB_OSTDL_PORTx(i));
> 
> The code does not look good. You have already a dereference at line
> 244:
> 
> 	const u8 *larbostd = larb->larb_gen->ostd[larb->larbid];

if larb->larb_gen->ostd is null, larbostd is the offset, e.g. 0x80 in
the log above. thus, we can not use "larbostd[i]" in the "for" loop.

sorry for the unreadable. In this case, is the change ok?

or like this:

-const u8 *larbostd = larb->larb_gen->ostd[larb->larbid];
+const u8 *larbostd = larb->larb_gen->ostd ? larb->larb_gen-ostd[larb-
>larbid] : NULL;

or add a explicit "if":
 if (larb->larb_gen->ostd)
   larbostd = xxx.

Which one do you prefer?

Thanks.

> 
> You are not fixing the NULL pointer dereference.
> 
> >  
> >  	for_each_set_bit(i, (unsigned long *)larb->mmu, 32) {
> > 
> 
> 
> Best regards,
> Krzysztof