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Subject: Re: [PATCH 5.5 regression fix 2/2] efi/libstub/helper: Initialize
 pointer variables to zero for mixed mode
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        the arch/x86 maintainers <x86@kernel.org>,
        linux-efi <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
References: <20191212103158.4958-1-hdegoede@redhat.com>
 <20191212103158.4958-3-hdegoede@redhat.com>
 <CAKv+Gu9AjYVvLot9+enuwSWfyfzqgCWSuW3ioccm3FJ7KFA8eA@mail.gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <82c65f05-1140-e10e-ba2f-0c4c5c85bbc8@redhat.com>
Date:   Thu, 12 Dec 2019 13:45:05 +0100
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Hi,

On 12-12-2019 12:29, Ard Biesheuvel wrote:
> On Thu, 12 Dec 2019 at 11:32, Hans de Goede <hdegoede@redhat.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@vger.kernel.org
>> Signed-off-by: Hans de Goede <hdegoede@redhat.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?

And "efi_file_io_interface_t *io" and "efi_file_handle_t *fh"
in efi_open_volume().

I think that is all of them.

Regards,

Hans