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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Tue, 13 Nov 2018 14:50:52 -0800
Message-ID: <CAKv+Gu8FK7=gcRVg--GX3LMA9fmGtvMkxDuXF8UEWuGpKq4HTA@mail.gmail.com>
Subject: Re: [PATCH] firmware: efi: add NULL pointer checks in efivars api functions
To:     Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc:     linux-efi <linux-efi@vger.kernel.org>,
        "<linux-wireless@vger.kernel.org>" <linux-wireless@vger.kernel.org>,
        Kalle Valo <kvalo@codeaurora.org>,
        Hans de Goede <hdegoede@redhat.com>
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Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

Hi Arend,

On Tue, 13 Nov 2018 at 12:51, Arend van Spriel
<arend.vanspriel@broadcom.com> wrote:
>
> Since commit ce2e6db554fa ("brcmfmac: Add support for getting nvram
> contents from EFI variables") we have a device driver accessing the
> efivars api (since next-20181107). Several functions in efivars api
> assume __efivars is set, ie. will be accessed after efivars_register()
> has been called. However, following NULL pointer access was reported
> calling efivar_entry_size() from the brcmfmac device driver.
>
> [   14.177769] Unable to handle kernel NULL pointer dereference at
>                 virtual address 00000008
> [   14.197303] pgd = 60bfa5f1
> [   14.211842] [00000008] *pgd=00000000
> [   14.227373] Internal error: Oops: 5 [#1] SMP ARM
> [   14.244244] Modules linked in: brcmfmac sha256_generic sha256_arm snd cfg80211 brcmutil soundcore snd_soc_tegra30_ahub tegra_wdt
> [   14.269109] CPU: 1 PID: 114 Comm: kworker/1:2 Not tainted 4.20.0-rc1-next-20181107-gd881de3 #1
> [   14.269114] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
> [   14.269154] Workqueue: events request_firmware_work_func
> [   14.269177] PC is at efivar_entry_size+0x28/0x90
> [   14.269362] LR is at brcmf_fw_complete_request+0x3f8/0x8d4 [brcmfmac]
> [   14.269369] pc : [<c0c40718>]    lr : [<bf2a3ef4>]    psr: a00d0113
> [   14.269374] sp : ede7fe28  ip : ee983410  fp : c1787f30
> [   14.269378] r10: 00000000  r9 : 00000000  r8 : bf2b2258
> [   14.269384] r7 : ee983000  r6 : c1604c48  r5 : ede7fe88  r4 : edf337c0
> [   14.269389] r3 : 00000000  r2 : 00000000  r1 : ede7fe88  r0 : c17712c8
> [   14.269398] Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
> [   14.269404] Control: 10c5387d  Table: ad16804a  DAC: 00000051
>
> Disassembly showed that the local static variable __efivars is NULL. Likely
> because efivars_register() is not called on this Tegra platform. So adding
> a NULL pointer check in efivar_entry_size() and similar functions while at
> it. In efivars_register() a couple of sanity checks have been added.
>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Reported-by: Jon Hunter <jonathanh@nvidia.com>
> Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
> ---
>  drivers/firmware/efi/vars.c | 108 +++++++++++++++++++++++++++++++++++---------
>  1 file changed, 87 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index 9336ffd..5fbd8e7 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -318,7 +318,12 @@ struct variable_validate {
>  static efi_status_t
>  check_var_size(u32 attributes, unsigned long size)
>  {
> -       const struct efivar_operations *fops = __efivars->ops;
> +       const struct efivar_operations *fops;
> +
> +       if (!__efivars)
> +               return EFI_UNSUPPORTED;
> +
> +       fops = __efivars->ops;
>
>         if (!fops->query_variable_store)
>                 return EFI_UNSUPPORTED;
> @@ -329,7 +334,12 @@ struct variable_validate {
>  static efi_status_t
>  check_var_size_nonblocking(u32 attributes, unsigned long size)
>  {
> -       const struct efivar_operations *fops = __efivars->ops;
> +       const struct efivar_operations *fops;
> +
> +       if (!__efivars)
> +               return EFI_UNSUPPORTED;
> +
> +       fops = __efivars->ops;
>
>         if (!fops->query_variable_store)
>                 return EFI_UNSUPPORTED;
> @@ -429,13 +439,18 @@ static void dup_variable_bug(efi_char16_t *str16, efi_guid_t *vendor_guid,
>  int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
>                 void *data, bool duplicates, struct list_head *head)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         unsigned long variable_name_size = 1024;
>         efi_char16_t *variable_name;
>         efi_status_t status;
>         efi_guid_t vendor_guid;
>         int err = 0;
>
> +       if (!__efivars)
> +               return -EFAULT;
> +
> +       ops = __efivars->ops;
> +
>         variable_name = kzalloc(variable_name_size, GFP_KERNEL);
>         if (!variable_name) {
>                 printk(KERN_ERR "efivars: Memory allocation failed.\n");
> @@ -583,12 +598,14 @@ static void efivar_entry_list_del_unlock(struct efivar_entry *entry)
>   */
>  int __efivar_entry_delete(struct efivar_entry *entry)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
>         efi_status_t status;
>
> -       status = ops->set_variable(entry->var.VariableName,
> -                                  &entry->var.VendorGuid,
> -                                  0, 0, NULL);
> +       if (!__efivars)
> +               return -EINVAL;
> +
> +       status = __efivars->ops->set_variable(entry->var.VariableName,
> +                                             &entry->var.VendorGuid,
> +                                             0, 0, NULL);
>
>         return efi_status_to_err(status);
>  }
> @@ -607,12 +624,17 @@ int __efivar_entry_delete(struct efivar_entry *entry)
>   */
>  int efivar_entry_delete(struct efivar_entry *entry)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_status_t status;
>
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
>

Any reason in particular you put the check after the lock is taken? Is
this to ensure that __efivars does not change under your feet?

> +       if (!__efivars) {
> +               up(&efivars_lock);
> +               return -EINVAL;
> +       }
> +       ops = __efivars->ops;
>         status = ops->set_variable(entry->var.VariableName,
>                                    &entry->var.VendorGuid,
>                                    0, 0, NULL);
> @@ -650,13 +672,19 @@ int efivar_entry_delete(struct efivar_entry *entry)
>  int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
>                      unsigned long size, void *data, struct list_head *head)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_status_t status;
>         efi_char16_t *name = entry->var.VariableName;
>         efi_guid_t vendor = entry->var.VendorGuid;
>
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
> +
> +       if (!__efivars) {
> +               up(&efivars_lock);
> +               return -EINVAL;
> +       }
> +       ops = __efivars->ops;
>         if (head && efivar_entry_find(name, vendor, head, false)) {
>                 up(&efivars_lock);
>                 return -EEXIST;
> @@ -687,12 +715,17 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
>  efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
>                              u32 attributes, unsigned long size, void *data)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_status_t status;
>
>         if (down_trylock(&efivars_lock))
>                 return -EBUSY;
>
> +       if (!__efivars) {
> +               up(&efivars_lock);
> +               return -EINVAL;
> +       }
> +
>         status = check_var_size_nonblocking(attributes,
>                                             size + ucs2_strsize(name, 1024));
>         if (status != EFI_SUCCESS) {
> @@ -700,6 +733,7 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
>                 return -ENOSPC;
>         }
>
> +       ops = __efivars->ops;
>         status = ops->set_variable_nonblocking(name, &vendor, attributes,
>                                                size, data);
>
> @@ -727,9 +761,13 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
>  int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
>                           bool block, unsigned long size, void *data)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_status_t status;
>
> +       if (!__efivars)
> +               return -EINVAL;
> +
> +       ops = __efivars->ops;
>         if (!ops->query_variable_store)
>                 return -ENOSYS;
>
> @@ -829,13 +867,18 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
>   */
>  int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_status_t status;
>
>         *size = 0;
>
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
> +       if (!__efivars) {
> +               up(&efivars_lock);
> +               return -EINVAL;
> +       }
> +       ops = __efivars->ops;
>         status = ops->get_variable(entry->var.VariableName,
>                                    &entry->var.VendorGuid, NULL, size, NULL);
>         up(&efivars_lock);
> @@ -861,12 +904,14 @@ int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
>  int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
>                        unsigned long *size, void *data)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
>         efi_status_t status;
>
> -       status = ops->get_variable(entry->var.VariableName,
> -                                  &entry->var.VendorGuid,
> -                                  attributes, size, data);
> +       if (!__efivars)
> +               return -EINVAL;
> +
> +       status = __efivars->ops->get_variable(entry->var.VariableName,
> +                                             &entry->var.VendorGuid,
> +                                             attributes, size, data);
>
>         return efi_status_to_err(status);
>  }
> @@ -882,14 +927,19 @@ int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
>  int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
>                      unsigned long *size, void *data)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
>         efi_status_t status;
>
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
> -       status = ops->get_variable(entry->var.VariableName,
> -                                  &entry->var.VendorGuid,
> -                                  attributes, size, data);
> +
> +       if (!__efivars) {
> +               up(&efivars_lock);
> +               return -EINVAL;
> +       }
> +
> +       status = __efivars->ops->get_variable(entry->var.VariableName,
> +                                             &entry->var.VendorGuid,
> +                                             attributes, size, data);
>         up(&efivars_lock);
>
>         return efi_status_to_err(status);
> @@ -921,7 +971,7 @@ int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
>  int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
>                               unsigned long *size, void *data, bool *set)
>  {
> -       const struct efivar_operations *ops = __efivars->ops;
> +       const struct efivar_operations *ops;
>         efi_char16_t *name = entry->var.VariableName;
>         efi_guid_t *vendor = &entry->var.VendorGuid;
>         efi_status_t status;
> @@ -940,6 +990,11 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
>
> +       if (!__efivars) {
> +               err = -EINVAL;
> +               goto out;
> +       }
> +
>         /*
>          * Ensure that the available space hasn't shrunk below the safe level
>          */
> @@ -956,6 +1011,8 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
>                 }
>         }
>
> +       ops = __efivars->ops;
> +
>         status = ops->set_variable(name, vendor, attributes, *size, data);
>         if (status != EFI_SUCCESS) {
>                 err = efi_status_to_err(status);
> @@ -1138,6 +1195,15 @@ int efivars_register(struct efivars *efivars,
>         if (down_interruptible(&efivars_lock))
>                 return -EINTR;
>
> +       if (WARN(!efivars || !ops, "Invalid parameters\n"))
> +               return -EINVAL;
> +
> +       /* check mandatory efivars operations */
> +       if (WARN_ON(!ops->get_variable) ||
> +           WARN_ON(!ops->set_variable) ||
> +           WARN_ON(!ops->get_next_variable))
> +               return -EINVAL;
> +
>         efivars->ops = ops;
>         efivars->kobject = kobject;
>
> --
> 1.9.1
>