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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Thu, 15 Nov 2018 05:54:12 -0800
Message-ID: <CAKv+Gu8oQeMLZo=DtvS+D=7GcadSrqhSX2pndHOr-KTQQ2fxPw@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
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On Tue, 13 Nov 2018 at 15:04, Arend van Spriel
<arend.vanspriel@broadcom.com> wrote:
>
> On 11/13/2018 11:50 PM, Ard Biesheuvel wrote:
> > 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?
>
> That was my reasoning although I am not sure if that is likely. Is
> efivars_register() always called before any drivers are started?
>

First of all, efivars_register() is only called on EFI systems, and
this Tegra is not an EFI system. So in general, it would be better if
your code checks efi_enabled(EFI_RUNTIME_SERVICES) before attempting
to access any EFI APIs, especially since CONFIG_EFI support can be
compiled out (in which case efi_enabled() resolves to a build time
constant 'false') Something like

--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c
@@ -446,7 +446,6 @@ struct brcmf_fw {

 static void brcmf_fw_request_done(const struct firmware *fw, void *ctx);

-#ifdef CONFIG_EFI
 /* In some cases the EFI-var stored nvram contains "ccode=ALL" or "ccode=XV"
  * to specify "worldwide" compatible settings, but these 2 ccode-s do not work
  * properly. "ccode=ALL" causes channels 12 and 13 to not be available,
@@ -478,6 +477,9 @@ static u8 *brcmf_fw_nvram_from_efi(size_t *data_len_ret)
        u8 *data = NULL;
        int err;

+       if (!efi_enabled(EFI_RUNTIME_SERVICES))
+               return NULL;
+
        nvram_efivar = kzalloc(sizeof(*nvram_efivar), GFP_KERNEL);
        if (!nvram_efivar)
                return NULL;
@@ -511,9 +513,6 @@ static u8 *brcmf_fw_nvram_from_efi(size_t *data_len_ret)
        kfree(nvram_efivar);
        return NULL;
 }
-#else
-static u8 *brcmf_fw_nvram_from_efi(size_t *data_len) { return NULL; }
-#endif

 static void brcmf_fw_free_request(struct brcmf_fw_request *req)
 {


Of course, that doesn't mean we should crash if you access the API
anyway, so I will queue this patch in efi/next as well. (I'll drop the
last hunk, though, if you don't mind - it returns with the lock held)

Thanks,
Ard.