[RFC PATCH] efi_loader: Fix EFI_VARIABLE_APPEND_WRITE hash check
Heinrich Schuchardt
xypron.glpk at gmx.de
Wed Apr 10 14:09:34 CEST 2024
On 10.04.24 13:53, Weizhao Ouyang wrote:
> On Thu, Apr 4, 2024 at 1:48 AM Weizhao Ouyang <o451686892 at gmail.com> wrote:
>>
>> Hi Heinrich,
>>
>> On Wed, Apr 3, 2024 at 10:54 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>>>
>>> On 27.03.24 15:06, Weizhao Ouyang wrote:
>>>> According to UEFI v2.10 spec section 8.2.6, if a caller invokes the
>>>> SetVariables() service, it will produce a digest from hash(VariableName,
>>>> VendorGuid, Attributes, TimeStamp, DataNew_variable_content), then the
>>>> firmware that implements the SetVariable() service will compare the
>>>> digest with the result of applying the signer’s public key to the
>>>> signature. For EFI variable append write, efitools sign-efi-sig-list has
>>>> an option "-a" to add EFI_VARIABLE_APPEND_WRITE attr, and u-boot will
>>>> drop this attribute in efi_set_variable_int(). So if a caller uses
>>>> "sign-efi-sig-list -a" to create the authenticated variable, this append
>>>> write will fail in the u-boot due to "hash check failed".
>>>
>>> Currently U-Boot does not allow to use EFI_VARIABLE_APPEND_WRITE for any
>>> non-existent variable, signed or not. This does not match the EDK II
>>> behavior.
>>
>> I'm not referring to the non-existent variable situation, it's a normal
>> existent variable update.
>>
>> I mean:
>> 1. process PK
>> 2. process KEK
>> 3. process a new APPEND_WRITE KEK (came from "sign-efi-sig-list -a ...",
>> so the digest and attrtibute of the KEK auth file will contain
>> APPEND_WRITE)
>> Then the hash check will fail.
>>
>>>
>>> There is a patch queued for this issue:
>>>
>>> [PATCH v2] efi_loader: fix append write behavior to non-existent variable
>>> https://lore.kernel.org/u-boot/20240402090950.3819705-1-kojima.masahisa@socionext.com/
>>>
>>> Could you, please, retest with that patch.
>>>
>>>>
>>>> This patch resumes writing the EFI_VARIABLE_APPEND_WRITE attr to ensure
>>>> that the hash check is correct. And also update the "test_efi_secboot"
>>>> test case to compliance with the change.
>>>>
>>>> Signed-off-by: Weizhao Ouyang <o451686892 at gmail.com>
>>>> ---
>>>> lib/efi_loader/efi_variable.c | 3 +--
>>>> test/py/tests/test_efi_secboot/conftest.py | 10 ++++++++++
>>>> test/py/tests/test_efi_secboot/test_authvar.py | 4 ++--
>>>> test/py/tests/test_efi_secboot/test_signed.py | 10 +++++-----
>>>> 4 files changed, 18 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
>>>> index 40f7a0fb10..f41aa8f9ad 100644
>>>> --- a/lib/efi_loader/efi_variable.c
>>>> +++ b/lib/efi_loader/efi_variable.c
>>>> @@ -259,7 +259,6 @@ efi_status_t efi_set_variable_int(const u16 *variable_name,
>>>> /* check if a variable exists */
>>>> var = efi_var_mem_find(vendor, variable_name, NULL);
>>>> append = !!(attributes & EFI_VARIABLE_APPEND_WRITE);
>>>> - attributes &= ~(u32)EFI_VARIABLE_APPEND_WRITE;
>>>
>>> According to the UEFI specification for GetVariable():
>>>
>>> "The EFI_VARIABLE_APPEND_WRITE attribute will never be set in the
>>> returned Attributes bitmask parameter."
>>
>> Yes, that's why I called it a RFC patch.
>>
>>>
>>> We don't want to set EFI_VARIABLE_APPEND_WRITE in a variable when
>>> calling efi_var_mem_ins().
>>
>> The APPEND_WRITE attribute is allowed to be set prior to invoking the
>> service (UEFI section 8.2.6). So anyway we should consider compatibility
>> with this case, along with making changes to GetVariable().
>
> Part of the process in edk2 is:
>
> VerifyTimeBasedPayloadAndUpdate
> --> VerifyTimeBasedPayload // calculate digest and compare digest
> --> AuthServiceInternalUpdateVariableWithTimeStamp
> --> VariableExLibUpdateVariable
> --> UpdateVariable // unset the APPEND_WRITE
>
> We can align with this implementation.
I was referring to the attribute value passed to efi_var_mem_ins(), not
to the value passed to SetVariable().
efi_var_mem_ins() does not remove the EFI_VARIABLE_APPEND_WRITE bit. The
code calling efi_var_mem_ins() should not pass such a value.
Best regards
Heinrich
>
> BR,
> Weizhao
>
>>
>> BR,
>> Weizhao
>>
>>>
>>>> delete = !append && (!data_size || !attributes);
>>>>
>>>> /* check attributes */
>>>> @@ -275,7 +274,7 @@ efi_status_t efi_set_variable_int(const u16 *variable_name,
>>>>
>>>> /* attributes won't be changed */
>>>> if (!delete &&
>>>> - ((ro_check && var->attr != attributes) ||
>>>> + ((ro_check && var->attr != (attributes & ~(u32)EFI_VARIABLE_APPEND_WRITE)) ||
>>>> (!ro_check && ((var->attr & ~(u32)EFI_VARIABLE_READ_ONLY)
>>>
>>> The (u32) conversions are superfluous.
>>>
>>> Best regards
>>>
>>> Heinrich
>>>
>>>> != (attributes & ~(u32)EFI_VARIABLE_READ_ONLY))))) {
>>>> return EFI_INVALID_PARAMETER;
>>>> diff --git a/test/py/tests/test_efi_secboot/conftest.py b/test/py/tests/test_efi_secboot/conftest.py
>>>> index ff7ac7c810..0fa0747fc7 100644
>>>> --- a/test/py/tests/test_efi_secboot/conftest.py
>>>> +++ b/test/py/tests/test_efi_secboot/conftest.py
>>>> @@ -64,6 +64,12 @@ def efi_boot_env(request, u_boot_config):
>>>> check_call('cd %s; %scert-to-efi-sig-list -g %s db1.crt db1.esl; %ssign-efi-sig-list -t "2020-04-05" -c KEK.crt -k KEK.key db db1.esl db1.auth'
>>>> % (mnt_point, EFITOOLS_PATH, GUID, EFITOOLS_PATH),
>>>> shell=True)
>>>> + # db2 (APPEND_WRITE)
>>>> + check_call('cd %s; openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_db2/ -keyout db2.key -out db2.crt -nodes -days 365'
>>>> + % mnt_point, shell=True)
>>>> + check_call('cd %s; %scert-to-efi-sig-list -g %s db2.crt db2.esl; %ssign-efi-sig-list -a -c KEK.crt -k KEK.key db db2.esl db2.auth'
>>>> + % (mnt_point, EFITOOLS_PATH, GUID, EFITOOLS_PATH),
>>>> + shell=True)
>>>> # dbx (TEST_dbx certificate)
>>>> check_call('cd %s; openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_dbx/ -keyout dbx.key -out dbx.crt -nodes -days 365'
>>>> % mnt_point, shell=True)
>>>> @@ -84,6 +90,10 @@ def efi_boot_env(request, u_boot_config):
>>>> check_call('cd %s; %scert-to-efi-hash-list -g %s -s 256 db1.crt dbx_hash1.crl; %ssign-efi-sig-list -t "2020-04-06" -c KEK.crt -k KEK.key dbx dbx_hash1.crl dbx_hash1.auth'
>>>> % (mnt_point, EFITOOLS_PATH, GUID, EFITOOLS_PATH),
>>>> shell=True)
>>>> + # dbx_hash2 (digest of TEST_db2 certificate, with APPEND_WRITE)
>>>> + check_call('cd %s; %scert-to-efi-hash-list -g %s -s 256 db2.crt dbx_hash2.crl; %ssign-efi-sig-list -a -c KEK.crt -k KEK.key dbx dbx_hash2.crl dbx_hash2.auth'
>>>> + % (mnt_point, EFITOOLS_PATH, GUID, EFITOOLS_PATH),
>>>> + shell=True)
>>>> # dbx_db (with TEST_db certificate)
>>>> check_call('cd %s; %ssign-efi-sig-list -t "2020-04-05" -c KEK.crt -k KEK.key dbx db.esl dbx_db.auth'
>>>> % (mnt_point, EFITOOLS_PATH),
>>>> diff --git a/test/py/tests/test_efi_secboot/test_authvar.py b/test/py/tests/test_efi_secboot/test_authvar.py
>>>> index f99b8270a6..d5aeb65048 100644
>>>> --- a/test/py/tests/test_efi_secboot/test_authvar.py
>>>> +++ b/test/py/tests/test_efi_secboot/test_authvar.py
>>>> @@ -183,7 +183,7 @@ class TestEfiAuthVar(object):
>>>> assert 'db:' in ''.join(output)
>>>>
>>>> output = u_boot_console.run_command_list([
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -a -i 4000000:$filesize db'])
>>>> assert 'Failed to set EFI variable' in ''.join(output)
>>>>
>>>> @@ -197,7 +197,7 @@ class TestEfiAuthVar(object):
>>>> with u_boot_console.log.section('Test Case 3c'):
>>>> # Test Case 3c, update with correct signature
>>>> output = u_boot_console.run_command_list([
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize db',
>>>> 'printenv -e -n -guid d719b2cb-3d3a-4596-a3bc-dad00e67656f db'])
>>>> assert 'Failed to set EFI variable' not in ''.join(output)
>>>> diff --git a/test/py/tests/test_efi_secboot/test_signed.py b/test/py/tests/test_efi_secboot/test_signed.py
>>>> index 2f862a259a..34719ad1f2 100644
>>>> --- a/test/py/tests/test_efi_secboot/test_signed.py
>>>> +++ b/test/py/tests/test_efi_secboot/test_signed.py
>>>> @@ -177,7 +177,7 @@ class TestEfiSignedImage(object):
>>>> with u_boot_console.log.section('Test Case 5b'):
>>>> # Test Case 5b, authenticated if both signatures are verified
>>>> output = u_boot_console.run_command_list([
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize db'])
>>>> assert 'Failed to set EFI variable' not in ''.join(output)
>>>> output = u_boot_console.run_command_list([
>>>> @@ -201,7 +201,7 @@ class TestEfiSignedImage(object):
>>>> with u_boot_console.log.section('Test Case 5d'):
>>>> # Test Case 5d, rejected if both of signatures are revoked
>>>> output = u_boot_console.run_command_list([
>>>> - 'fatload host 0:1 4000000 dbx_hash1.auth',
>>>> + 'fatload host 0:1 4000000 dbx_hash2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize dbx'])
>>>> assert 'Failed to set EFI variable' not in ''.join(output)
>>>> output = u_boot_console.run_command_list([
>>>> @@ -223,7 +223,7 @@ class TestEfiSignedImage(object):
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize KEK',
>>>> 'fatload host 0:1 4000000 PK.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize PK',
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize db',
>>>> 'fatload host 0:1 4000000 dbx_hash1.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize dbx'])
>>>> @@ -300,7 +300,7 @@ class TestEfiSignedImage(object):
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize KEK',
>>>> 'fatload host 0:1 4000000 PK.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize PK',
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize db',
>>>> 'fatload host 0:1 4000000 dbx_hash384.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize dbx'])
>>>> @@ -323,7 +323,7 @@ class TestEfiSignedImage(object):
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize KEK',
>>>> 'fatload host 0:1 4000000 PK.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize PK',
>>>> - 'fatload host 0:1 4000000 db1.auth',
>>>> + 'fatload host 0:1 4000000 db2.auth',
>>>> 'setenv -e -nv -bs -rt -at -a -i 4000000:$filesize db',
>>>> 'fatload host 0:1 4000000 dbx_hash512.auth',
>>>> 'setenv -e -nv -bs -rt -at -i 4000000:$filesize dbx'])
>>>
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