linux-kernel - Re: [PATCH] perf/x86/intel/uncore: Avoid null dereferences (uncore_extra_pci

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Date:   Thu, 15 Apr 2021 17:19:01 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Steve Wahl <steve.wahl@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86/intel/uncore: Avoid null dereferences
 (uncore_extra_pci_dev)

Hi Steve,

On 4/15/2021 4:37 PM, Steve Wahl wrote:
> If an uncore has no pci_init routine, or that routine fails,
> uncore_pci_init is not called, and memory is not allocated for
> uncore_extra_pci_dev.
> 
> So check to make sure uncore_extra_pci_dev is not NULL before use.
>

I think more after yesterday's discussion. There may be a better 
solution than this.

Actually, we don't have to probe all the PCU devices and stores them 
into the uncore_extra_pci_dev for the cpu_init().
We just need to pick up the first PCU device and check the existence of 
the SBOX once.

I will send out a patch shortly.

> And fix the case that led us to discover the null derefs; don't fail
> snbep_pci2phy_map_init if BIOS doesn't supply pcibus_to_node
> information.
> 
> Fixes: 9a7832ce3d92 ("perf/x86/intel/uncore: With > 8 nodes, get pci bus die id from NUMA info")

In theory, the pci_read_config_dword() may fails as well. It has 
possible that the issue can still be observed before the "> 8 nodes" patch.

I think the fixes should be 5306c31c5733 ("perf/x86/uncore/hsw-ep: 
Handle systems with only two SBOXes")

Thanks,
Kan

> Signed-off-by: Steve Wahl <steve.wahl@....com>
> ---
>   arch/x86/events/intel/uncore_snbep.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
> index b79951d0707c..14c24356a2fa 100644
> --- a/arch/x86/events/intel/uncore_snbep.c
> +++ b/arch/x86/events/intel/uncore_snbep.c
> @@ -1373,11 +1373,11 @@ static int snbep_pci2phy_map_init(int devid, int nodeid_loc, int idmap_loc, bool
>   		/*
>   		 * The nodeid and idmap registers only contain enough
>   		 * information to handle 8 nodes.  On systems with more
> -		 * than 8 nodes, we need to rely on NUMA information,
> +		 * than 8 nodes, if available we rely on NUMA information,
>   		 * filled in from BIOS supplied information, to determine
>   		 * the topology.
>   		 */
> -		if (nr_node_ids <= 8) {
> +		if ((nr_node_ids <= 8) || (pcibus_to_node(ubox_dev->bus) == -1)) {
>   			/* get the Node ID of the local register */
>   			err = pci_read_config_dword(ubox_dev, nodeid_loc, &config);
>   			if (err)
> @@ -2865,7 +2865,9 @@ void hswep_uncore_cpu_init(void)
>   		hswep_uncore_cbox.num_boxes = boot_cpu_data.x86_max_cores;
>   
>   	/* Detect 6-8 core systems with only two SBOXes */
> -	if (uncore_extra_pci_dev[pkg].dev[HSWEP_PCI_PCU_3]) {
> +	if (!uncore_extra_pci_dev)
> +		hswep_uncore_sbox.num_boxes = 2;
> +	else if (uncore_extra_pci_dev[pkg].dev[HSWEP_PCI_PCU_3]) {
>   		u32 capid4;
>   
>   		pci_read_config_dword(uncore_extra_pci_dev[pkg].dev[HSWEP_PCI_PCU_3],
> @@ -3243,6 +3245,8 @@ void bdx_uncore_cpu_init(void)
>   	if (boot_cpu_data.x86_model == 86) {
>   		uncore_msr_uncores[BDX_MSR_UNCORE_SBOX] = NULL;
>   	/* Detect systems with no SBOXes */
> +	} else if (!uncore_extra_pci_dev) {
> +		bdx_msr_uncores[BDX_MSR_UNCORE_SBOX] = NULL;
>   	} else if (uncore_extra_pci_dev[pkg].dev[HSWEP_PCI_PCU_3]) {
>   		struct pci_dev *pdev;
>   		u32 capid4;
>