Re: [PATCH] mtd: rawnand: qcom: fix memory corruption that causes panic

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Manivannan,

mani@kernel.org wrote on Thu, 14 Apr 2022 20:09:07 +0530:

> On Thu, Apr 14, 2022 at 02:42:36PM +0200, Miquel Raynal wrote:
> > Hi Md,
> > 
> > quic_mdalam@quicinc.com wrote on Thu, 14 Apr 2022 17:50:48 +0530:
> >   
> > > > Hi Md,
> > > >
> > > > quic_mdalam@quicinc.com wrote on Thu, 14 Apr 2022 11:09:33 +0530:
> > > >    
> > > >> This patch fixes a memory corruption that occurred in the
> > > >> nand_scan() path for Hynix nand device.
> > > >>
> > > >> On boot, for Hynix nand device will panic at a weird place:
> > > >> | Unable to handle kernel NULL pointer dereference at virtual
> > > >>    address 00000070
> > > >> | [00000070] *pgd=00000000
> > > >> | Internal error: Oops: 5 [#1] PREEMPT SMP ARM Modules linked in:
> > > >> | CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-01473-g13ae1769cfb0
> > > >>    #38
> > > >> | Hardware name: Generic DT based system PC is at
> > > >> | nandc_set_reg+0x8/0x1c LR is at qcom_nandc_command+0x20c/0x5d0
> > > >> | pc : [<c088b74c>]    lr : [<c088d9c8>]    psr: 00000113
> > > >> | sp : c14adc50  ip : c14ee208  fp : c0cc970c
> > > >> | r10: 000000a3  r9 : 00000000  r8 : 00000040
> > > >> | r7 : c16f6a00  r6 : 00000090  r5 : 00000004  r4 :c14ee040
> > > >> | r3 : 00000000  r2 : 0000000b  r1 : 00000000  r0 :c14ee040
> > > >> | Flags: nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM Segment none
> > > >> | Control: 10c5387d  Table: 8020406a  DAC: 00000051 Register r0
> > > >> | information: slab kmalloc-2k start c14ee000 pointer offset
> > > >>    64 size 2048
> > > >> | Process swapper/0 (pid: 1, stack limit = 0x(ptrval)) nandc_set_reg
> > > >> | from qcom_nandc_command+0x20c/0x5d0 qcom_nandc_command from
> > > >> | nand_readid_op+0x198/0x1e8 nand_readid_op from
> > > >> | hynix_nand_has_valid_jedecid+0x30/0x78
> > > >> | hynix_nand_has_valid_jedecid from hynix_nand_init+0xb8/0x454
> > > >> | hynix_nand_init from nand_scan_with_ids+0xa30/0x14a8
> > > >> | nand_scan_with_ids from qcom_nandc_probe+0x648/0x7b0
> > > >> | qcom_nandc_probe from platform_probe+0x58/0xac
> > > >>
> > > >> The problem is that the nand_scan()'s qcom_nand_attach_chip callback
> > > >> is updating the nandc->max_cwperpage from 1 to 4.This causes the
> > > >> sg_init_table of clear_bam_transaction() in the driver's
> > > >> qcom_nandc_command() to memset much more than what was initially
> > > >> allocated by alloc_bam_transaction().    
> > > > Thanks for investigating!
> > > >    
> > > >> This patch will update nandc->max_cwperpage 1 to 4 after nand_scan()
> > > >> returns, and remove updating nandc->max_cwperpage from
> > > >> qcom_nand_attach_chip call back.    
> > > > The fix does not look right, as far as I understand, this should be properly handled during the attach phase. That is where we have all information about the chip and do the configuration for this chip.
> > > >
> > > > If you update max_cwperpage there you should probably update other internal variables that depend on it as well.    
> > > 
> > >     Currently we are updating max_cwperpage  in qcom_nand_attach_chip(), but we are seeing issue for Hynix nand device since nand_scan_tail() is getting called after nand_attach() and in nand_attach() we are updating max_cwperpage to 4 or 8 based on page size.
> > > 
> > >      From nand_scan_tail() there is a call for nand_manufacturer_init() , specific to Hynix nand read_id is getting called that's why we are seeing this issue only for Hynix nand device. Read id sequence as below
> > > 
> > >     hynix_nand_has_valid_jedecid()
> > > 
> > >                  |
> > > 
> > >     nand_readid_op()
> > > 
> > >               |
> > > 
> > >   qcom_nandc_command()
> > > 
> > >              |
> > > 
> > > pre_command()
> > > 
> > >            |
> > > 
> > > clear_bam_transaction()   --> In this call we are doing sg_init_table() which is calling memset() based on max_cwperpage.Since initially we have allocated bam transaction as per max_cwperpage =1 and , since nand_chip_attach() updated max_cwperpage,  now we are doing memset as per max_cwperpage = 4 or 8.
> > > 
> > > 
> > > So anyway we have to updated max_cwperpage after nand_scan() call only.  Since there is no other dependency on max_cwperpage in nand_attach_chip() and we are using this in bam_alloc() and bam_clear().  
> > 
> > Why don't you update the sg table after increasing max_cwperpage?
> >   
> 
> Or we could move the bam reallocation inside qcom_nand_attach_chip() as below?

Much better approach, yes.

> 
> diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
> index 7c6efa3b6255..58c16054630f 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -2653,9 +2653,23 @@ static int qcom_nand_attach_chip(struct nand_chip *chip)
>  
>         mtd_set_ooblayout(mtd, &qcom_nand_ooblayout_ops);
>  
> +       /* Free the initially allocated BAM transaction for reading the ONFI params */
> +       if (nandc->props->is_bam)
> +               free_bam_transaction(nandc);
> +
>         nandc->max_cwperpage = max_t(unsigned int, nandc->max_cwperpage,
>                                      cwperpage);
>  
> +       /* Now allocate the BAM transaction based on updated max_cwperpage */
> +       if (nandc->props->is_bam) {
> +               nandc->bam_txn = alloc_bam_transaction(nandc);
> +               if (!nandc->bam_txn) {
> +                       dev_err(nandc->dev,
> +                               "failed to allocate bam transaction\n");
> +                       return -ENOMEM;
> +               }
> +       }
> +
>         /*
>          * DATA_UD_BYTES varies based on whether the read/write command protects
>          * spare data with ECC too. We protect spare data by default, so we set
> @@ -2956,17 +2970,6 @@ static int qcom_nand_host_init_and_register(struct qcom_nand_controller *nandc,
>         if (ret)
>                 return ret;
>  
> -       if (nandc->props->is_bam) {
> -               free_bam_transaction(nandc);
> -               nandc->bam_txn = alloc_bam_transaction(nandc);
> -               if (!nandc->bam_txn) {
> -                       dev_err(nandc->dev,
> -                               "failed to allocate bam transaction\n");
> -                       nand_cleanup(chip);
> -                       return -ENOMEM;
> -               }
> -       }
> -
>         ret = mtd_device_parse_register(mtd, probes, NULL, NULL, 0);
>         if (ret)
>                 nand_cleanup(chip);
> 
> Thanks,
> Mani


Thanks,
Miquèl

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