Re: [PATCH 5.15.y] phy: qcom: qmp: Fix NULL pointer dereference for USB Uni PHYs

[Krishna Kurapati <quic_kriskura@quicinc.com>]

On 11/15/2024 9:29 PM, Dmitry Baryshkov wrote:
> On Fri, Nov 15, 2024 at 02:45:45PM +0530, Krishna Kurapati wrote:
>> Commit [1] introduced DP support to QMP driver. While doing so, the
>> dp and usb configuration structures were added to a combo_phy_cfg
>> structure. During probe, the match data is used to parse and identify the
>> dp and usb configs separately. While doing so, the usb_cfg variable
>> represents the configuration parameters for USB part of the phy (whether
>> it is DP-Cobo or Uni). during probe, one corner case of parsing usb_cfg
>> for Uni PHYs is left incomplete and it is left as NULL. This NULL variable
>> further percolates down to qmp_phy_create() call essentially getting
>> de-referenced and causing a crash.
> 
> The UNI PHY platforms don't have usb3-phy subnode. As such the usb_cfg
> variable should not be used in the for_each_available_child_of_node()
> loop.
> 
> Please provide details for the platform on which you observe the crash
> and the backtrace.
> 

I got this error when I started working on multiport support (begining 
of 2023). Initially I tried testing on my code on 5.15, hence this patch 
was raised on the same.

The 2 qmp phys on sa8195 and sa8295 (based on sc8280xp) are uni phy and 
the following was the DT node that worked out for me on 5.15 codebase:


	usb_1_qmpphy: ssphy@88eb000 {
		compatible = "qcom,sm8150-qmp-usb3-uni-phy";
		reg = <0x088eb000 0x200>;
		#address-cells = <1>;
		#size-cells = <1>;
		ranges;
		//status = "disabled";
		clocks = <&gcc GCC_USB3_MP_PHY_AUX_CLK>,
			 <&rpmhcc RPMH_CXO_CLK>,
			 <&gcc GCC_USB3_SEC_CLKREF_CLK>,
			 <&gcc GCC_USB3_MP_PHY_COM_AUX_CLK>;
		clock-names = "aux", "ref_clk_src", "ref", "com_aux";

		resets = <&gcc GCC_USB3UNIPHY_PHY_MP0_BCR>,
			 <&gcc GCC_USB3_UNIPHY_MP0_BCR>;
		reset-names = "phy", "common";

		//vdda-phy-supply = <&L3C>;
		vdda-pll-supply = <&L5E>;

		usb_1_ssphy: usb3-phy@88eb200 {
			reg = <0x088eb200 0x200>,
			      <0x088eb400 0x200>,
			      <0x088eb800 0x800>,
			      <0x088eb600 0x200>;
			#clock-cells = <0>;
			#phy-cells = <0>;
			clocks = <&gcc GCC_USB3_MP_PHY_PIPE_0_CLK>;
			clock-names = "pipe0";
			clock-output-names = "usb3_uni_phy_pipe_clk_src";
		};
	};


I was hitting the bug when I write the DT above way on top of 5.15 baseline.

In 5.15.y, the SM8150 usb_2_qmpphy dT is as follows:

                 usb_2_qmpphy: phy@88eb000 {
                         compatible = "qcom,sm8150-qmp-usb3-uni-phy";
                         reg = <0 0x088eb000 0 0x200>;
                         status = "disabled";
                         #address-cells = <2>;
                         #size-cells = <2>;
                         ranges;

                         clocks = <&gcc GCC_USB3_SEC_PHY_AUX_CLK>,
                                  <&rpmhcc RPMH_CXO_CLK>,
                                  <&gcc GCC_USB3_SEC_CLKREF_CLK>,
                                  <&gcc GCC_USB3_SEC_PHY_COM_AUX_CLK>;
                         clock-names = "aux", "ref_clk_src", "ref", 
"com_aux";

                         resets = <&gcc GCC_USB3PHY_PHY_SEC_BCR>,
                                  <&gcc GCC_USB3_PHY_SEC_BCR>;
                         reset-names = "phy", "common";

                         usb_2_ssphy: phy@88eb200 {
                                 reg = <0 0x088eb200 0 0x200>,
                                       <0 0x088eb400 0 0x200>,
                                       <0 0x088eb800 0 0x800>,
                                       <0 0x088eb600 0 0x200>;
                                 #clock-cells = <0>;
                                 #phy-cells = <0>;
                                 clocks = <&gcc GCC_USB3_SEC_PHY_PIPE_CLK>;
                                 clock-names = "pipe0";
                                 clock-output-names = 
"usb3_uni_phy_pipe_clk_src";
                         };
                 };

IIRC, when I tried using the above sm8150 dt on 5.15.y, the phy_create 
was (either not getting called) or crashing. Probably because 
"of_node_name_eq()" didn't find either "dp-phy" or "usb3-phy" and cfg 
variable was NULL.

I can try reproducing the issue and get back again in a week.

Apologies if I have misunderstood something and this patch doesn't make 
sense. Let me know if I have made any mistake anywhere (either in my DT) 
or in understanding.

Regards,
Krishna,