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

From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Yong Wu <yong.wu@mediatek.com>,
	Matthias Brugger <matthias.bgg@gmail.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>,
	Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Tomasz Figa <tfiga@chromium.org>,
	linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	iommu@lists.linux-foundation.org, youlin.pei@mediatek.com,
	anan.sun@mediatek.com, yi.kuo@mediatek.com,
	anthony.huang@mediatek.com, Ikjoon Jang <ikjn@chromium.org>
Subject: Re: [PATCH] memory: mtk-smi: Fix a null dereference for the ostd
Date: Fri, 29 Oct 2021 19:35:45 +0200	[thread overview]
Message-ID: <23b036d1-bdc4-da55-a800-03fc3dabd48e@canonical.com> (raw)
In-Reply-To: <20211028055056.26378-1-yong.wu@mediatek.com>

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@mediatek.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];

You are not fixing the NULL pointer dereference.

>  
>  	for_each_set_bit(i, (unsigned long *)larb->mmu, 32) {
> 

Best regards,
Krzysztof

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