linux-kernel - Re: [PATCH 5.5 regression fix 2/2] efi/libstub/helper: Initialize pointer variables to zero for mixed mode

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Date:   Thu, 12 Dec 2019 13:38:40 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 5.5 regression fix 2/2] efi/libstub/helper: Initialize
 pointer variables to zero for mixed mode

Hi,

On 12-12-2019 12:29, Ard Biesheuvel wrote:
> On Thu, 12 Dec 2019 at 11:32, Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> When running in EFI mixed mode (running a 64 bit kernel on 32 bit EFI
>> firmware), we _must_ initialize any pointers which are returned by
>> reference by an EFI call to NULL before making the EFI call.
>>
>> In mixed mode pointers are 64 bit, but when running on a 32 bit firmware,
>> EFI calls which return a pointer value by reference only fill the lower
>> 32 bits of the passed pointer, leaving the upper 32 bits uninitialized
>> unless we explicitly set them to 0 before the call.
>>
>> We have had this bug in the efi-stub-helper.c file reading code for
>> a while now, but this has likely not been noticed sofar because
>> this code only gets triggered when LILO style file=... arguments are
>> present on the kernel cmdline.
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>   drivers/firmware/efi/libstub/efi-stub-helper.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
>> index e02579907f2e..6ca7d86743af 100644
>> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
>> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
>> @@ -365,7 +365,7 @@ static efi_status_t efi_file_size(efi_system_table_t *sys_table_arg, void *__fh,
>>                                    u64 *file_sz)
>>   {
>>          efi_file_handle_t *h, *fh = __fh;
> 
> What about h? Doesn't it suffer from the same problem?
> 
>> -       efi_file_info_t *info;
>> +       efi_file_info_t *info = NULL;
>>          efi_status_t status;
>>          efi_guid_t info_guid = EFI_FILE_INFO_ID;
>>          unsigned long info_sz;
> 
> And info_sz?

You are right in both cases. I only checked allocate_pool and locate_protocol callers as those
are the usual suspects.

Shall I send a v2 of just this patch, or of the entire series, or are you going to
fix this up?

Regards,

Hans


> 
> 
>> @@ -527,7 +527,7 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>>                                    unsigned long *load_addr,
>>                                    unsigned long *load_size)
>>   {
>> -       struct file_info *files;
>> +       struct file_info *files = NULL;
>>          unsigned long file_addr;
>>          u64 file_size_total;
>>          efi_file_handle_t *fh = NULL;
>> --
>> 2.23.0
>>
>