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Date: Tue, 4 Jun 2024 14:12:05 -0700
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Subject: Re: [PATCH v9 08/19] x86: Secure Launch kernel early boot stub
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
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On 6/4/24 1:54 PM, Ard Biesheuvel wrote:
> On Tue, 4 Jun 2024 at 19:34, <ross.philipson@oracle.com> wrote:
>>
>> On 6/4/24 10:27 AM, Ard Biesheuvel wrote:
>>> On Tue, 4 Jun 2024 at 19:24, <ross.philipson@oracle.com> wrote:
>>>>
>>>> On 5/31/24 6:33 AM, Ard Biesheuvel wrote:
>>>>> On Fri, 31 May 2024 at 13:00, Ard Biesheuvel <ardb@kernel.org> wrote:
>>>>>>
>>>>>> Hello Ross,
>>>>>>
>>>>>> On Fri, 31 May 2024 at 03:32, Ross Philipson <ross.philipson@oracle.com> wrote:
>>>>>>>
>>>>>>> The Secure Launch (SL) stub provides the entry point for Intel TXT (and
>>>>>>> later AMD SKINIT) to vector to during the late launch. The symbol
>>>>>>> sl_stub_entry is that entry point and its offset into the kernel is
>>>>>>> conveyed to the launching code using the MLE (Measured Launch
>>>>>>> Environment) header in the structure named mle_header. The offset of the
>>>>>>> MLE header is set in the kernel_info. The routine sl_stub contains the
>>>>>>> very early late launch setup code responsible for setting up the basic
>>>>>>> environment to allow the normal kernel startup_32 code to proceed. It is
>>>>>>> also responsible for properly waking and handling the APs on Intel
>>>>>>> platforms. The routine sl_main which runs after entering 64b mode is
>>>>>>> responsible for measuring configuration and module information before
>>>>>>> it is used like the boot params, the kernel command line, the TXT heap,
>>>>>>> an external initramfs, etc.
>>>>>>>
>>>>>>> Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
>>>>>>> ---
>>>>>>>     Documentation/arch/x86/boot.rst        |  21 +
>>>>>>>     arch/x86/boot/compressed/Makefile      |   3 +-
>>>>>>>     arch/x86/boot/compressed/head_64.S     |  30 +
>>>>>>>     arch/x86/boot/compressed/kernel_info.S |  34 ++
>>>>>>>     arch/x86/boot/compressed/sl_main.c     | 577 ++++++++++++++++++++
>>>>>>>     arch/x86/boot/compressed/sl_stub.S     | 725 +++++++++++++++++++++++++
>>>>>>>     arch/x86/include/asm/msr-index.h       |   5 +
>>>>>>>     arch/x86/include/uapi/asm/bootparam.h  |   1 +
>>>>>>>     arch/x86/kernel/asm-offsets.c          |  20 +
>>>>>>>     9 files changed, 1415 insertions(+), 1 deletion(-)
>>>>>>>     create mode 100644 arch/x86/boot/compressed/sl_main.c
>>>>>>>     create mode 100644 arch/x86/boot/compressed/sl_stub.S
>>>>>>>
>>>>>>> diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst
>>>>>>> index 4fd492cb4970..295cdf9bcbdb 100644
>>>>>>> --- a/Documentation/arch/x86/boot.rst
>>>>>>> +++ b/Documentation/arch/x86/boot.rst
>>>>>>> @@ -482,6 +482,14 @@ Protocol:  2.00+
>>>>>>>                - If 1, KASLR enabled.
>>>>>>>                - If 0, KASLR disabled.
>>>>>>>
>>>>>>> +  Bit 2 (kernel internal): SLAUNCH_FLAG
>>>>>>> +
>>>>>>> +       - Used internally by the setup kernel to communicate
>>>>>>> +         Secure Launch status to kernel proper.
>>>>>>> +
>>>>>>> +           - If 1, Secure Launch enabled.
>>>>>>> +           - If 0, Secure Launch disabled.
>>>>>>> +
>>>>>>>       Bit 5 (write): QUIET_FLAG
>>>>>>>
>>>>>>>            - If 0, print early messages.
>>>>>>> @@ -1028,6 +1036,19 @@ Offset/size:     0x000c/4
>>>>>>>
>>>>>>>       This field contains maximal allowed type for setup_data and setup_indirect structs.
>>>>>>>
>>>>>>> +============   =================
>>>>>>> +Field name:    mle_header_offset
>>>>>>> +Offset/size:   0x0010/4
>>>>>>> +============   =================
>>>>>>> +
>>>>>>> +  This field contains the offset to the Secure Launch Measured Launch Environment
>>>>>>> +  (MLE) header. This offset is used to locate information needed during a secure
>>>>>>> +  late launch using Intel TXT. If the offset is zero, the kernel does not have
>>>>>>> +  Secure Launch capabilities. The MLE entry point is called from TXT on the BSP
>>>>>>> +  following a success measured launch. The specific state of the processors is
>>>>>>> +  outlined in the TXT Software Development Guide, the latest can be found here:
>>>>>>> +  https://urldefense.com/v3/__https://www.intel.com/content/dam/www/public/us/en/documents/guides/intel-txt-software-development-guide.pdf__;!!ACWV5N9M2RV99hQ!Mng0gnPhOYZ8D02t1rYwQfY6U3uWaypJyd1T2rsWz3QNHr9GhIZ9ANB_-cgPExxX0e0KmCpda-3VX8Fj$
>>>>>>> +
>>>>>>>
>>>>>>
>>>>>> Could we just repaint this field as the offset relative to the start
>>>>>> of kernel_info rather than relative to the start of the image? That
>>>>>> way, there is no need for patch #1, and given that the consumer of
>>>>>> this field accesses it via kernel_info, I wouldn't expect any issues
>>>>>> in applying this offset to obtain the actual address.
>>>>>>
>>>>>>
>>>>>>>     The Image Checksum
>>>>>>>     ==================
>>>>>>> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>>>>>>> index 9189a0e28686..9076a248d4b4 100644
>>>>>>> --- a/arch/x86/boot/compressed/Makefile
>>>>>>> +++ b/arch/x86/boot/compressed/Makefile
>>>>>>> @@ -118,7 +118,8 @@ vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
>>>>>>>     vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
>>>>>>>     vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
>>>>>>>
>>>>>>> -vmlinux-objs-$(CONFIG_SECURE_LAUNCH) += $(obj)/early_sha1.o $(obj)/early_sha256.o
>>>>>>> +vmlinux-objs-$(CONFIG_SECURE_LAUNCH) += $(obj)/early_sha1.o $(obj)/early_sha256.o \
>>>>>>> +       $(obj)/sl_main.o $(obj)/sl_stub.o
>>>>>>>
>>>>>>>     $(obj)/vmlinux: $(vmlinux-objs-y) FORCE
>>>>>>>            $(call if_changed,ld)
>>>>>>> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
>>>>>>> index 1dcb794c5479..803c9e2e6d85 100644
>>>>>>> --- a/arch/x86/boot/compressed/head_64.S
>>>>>>> +++ b/arch/x86/boot/compressed/head_64.S
>>>>>>> @@ -420,6 +420,13 @@ SYM_CODE_START(startup_64)
>>>>>>>            pushq   $0
>>>>>>>            popfq
>>>>>>>
>>>>>>> +#ifdef CONFIG_SECURE_LAUNCH
>>>>>>> +       /* Ensure the relocation region is coverd by a PMR */
>>>>>>
>>>>>> covered
>>>>>>
>>>>>>> +       movq    %rbx, %rdi
>>>>>>> +       movl    $(_bss - startup_32), %esi
>>>>>>> +       callq   sl_check_region
>>>>>>> +#endif
>>>>>>> +
>>>>>>>     /*
>>>>>>>      * Copy the compressed kernel to the end of our buffer
>>>>>>>      * where decompression in place becomes safe.
>>>>>>> @@ -462,6 +469,29 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
>>>>>>>            shrq    $3, %rcx
>>>>>>>            rep     stosq
>>>>>>>
>>>>>>> +#ifdef CONFIG_SECURE_LAUNCH
>>>>>>> +       /*
>>>>>>> +        * Have to do the final early sl stub work in 64b area.
>>>>>>> +        *
>>>>>>> +        * *********** NOTE ***********
>>>>>>> +        *
>>>>>>> +        * Several boot params get used before we get a chance to measure
>>>>>>> +        * them in this call. This is a known issue and we currently don't
>>>>>>> +        * have a solution. The scratch field doesn't matter. There is no
>>>>>>> +        * obvious way to do anything about the use of kernel_alignment or
>>>>>>> +        * init_size though these seem low risk with all the PMR and overlap
>>>>>>> +        * checks in place.
>>>>>>> +        */
>>>>>>> +       movq    %r15, %rdi
>>>>>>> +       callq   sl_main
>>>>>>> +
>>>>>>> +       /* Ensure the decompression location is covered by a PMR */
>>>>>>> +       movq    %rbp, %rdi
>>>>>>> +       movq    output_len(%rip), %rsi
>>>>>>> +       callq   sl_check_region
>>>>>>> +#endif
>>>>>>> +
>>>>>>> +       pushq   %rsi
>>>>>>
>>>>>> This looks like a rebase error.
>>>>>>
>>>>>>>            call    load_stage2_idt
>>>>>>>
>>>>>>>            /* Pass boot_params to initialize_identity_maps() */
>>>>>>> diff --git a/arch/x86/boot/compressed/kernel_info.S b/arch/x86/boot/compressed/kernel_info.S
>>>>>>> index c18f07181dd5..e199b87764e9 100644
>>>>>>> --- a/arch/x86/boot/compressed/kernel_info.S
>>>>>>> +++ b/arch/x86/boot/compressed/kernel_info.S
>>>>>>> @@ -28,6 +28,40 @@ SYM_DATA_START(kernel_info)
>>>>>>>            /* Maximal allowed type for setup_data and setup_indirect structs. */
>>>>>>>            .long   SETUP_TYPE_MAX
>>>>>>>
>>>>>>> +       /* Offset to the MLE header structure */
>>>>>>> +#if IS_ENABLED(CONFIG_SECURE_LAUNCH)
>>>>>>> +       .long   rva(mle_header)
>>>>>>
>>>>>> ... so this could just be mle_header - kernel_info, and the consumer
>>>>>> can do the math instead.
>>>>>>
>>>>>>> +#else
>>>>>>> +       .long   0
>>>>>>> +#endif
>>>>>>> +
>>>>>>>     kernel_info_var_len_data:
>>>>>>>            /* Empty for time being... */
>>>>>>>     SYM_DATA_END_LABEL(kernel_info, SYM_L_LOCAL, kernel_info_end)
>>>>>>> +
>>>>>>> +#if IS_ENABLED(CONFIG_SECURE_LAUNCH)
>>>>>>> +       /*
>>>>>>> +        * The MLE Header per the TXT Specification, section 2.1
>>>>>>> +        * MLE capabilities, see table 4. Capabilities set:
>>>>>>> +        * bit 0: Support for GETSEC[WAKEUP] for RLP wakeup
>>>>>>> +        * bit 1: Support for RLP wakeup using MONITOR address
>>>>>>> +        * bit 2: The ECX register will contain the pointer to the MLE page table
>>>>>>> +        * bit 5: TPM 1.2 family: Details/authorities PCR usage support
>>>>>>> +        * bit 9: Supported format of TPM 2.0 event log - TCG compliant
>>>>>>> +        */
>>>>>>> +SYM_DATA_START(mle_header)
>>>>>>> +       .long   0x9082ac5a  /* UUID0 */
>>>>>>> +       .long   0x74a7476f  /* UUID1 */
>>>>>>> +       .long   0xa2555c0f  /* UUID2 */
>>>>>>> +       .long   0x42b651cb  /* UUID3 */
>>>>>>> +       .long   0x00000034  /* MLE header size */
>>>>>>> +       .long   0x00020002  /* MLE version 2.2 */
>>>>>>> +       .long   rva(sl_stub_entry) /* Linear entry point of MLE (virt. address) */
>>>>>>
>>>>>> and these should perhaps be relative to mle_header?
>>>>>>
>>>>>>> +       .long   0x00000000  /* First valid page of MLE */
>>>>>>> +       .long   0x00000000  /* Offset within binary of first byte of MLE */
>>>>>>> +       .long   rva(_edata) /* Offset within binary of last byte + 1 of MLE */
>>>>>>
>>>>>> and here
>>>>>>
>>>>>
>>>>> Ugh never mind - these are specified externally.
>>>>
>>>> Can you clarify your follow on comment here?
>>>>
>>>
>>> I noticed that -as you pointed out in your previous reply- these
>>> fields cannot be repainted at will, as they are defined by an external
>>> specification.
>>>
>>> I'll play a bit more with this code tomorrow - I would *really* like
>>> to avoid the need for patch #1, as it adds another constraint on how
>>> we construct the boot image, and this is already riddled with legacy
>>> and other complications.
>>
>> Yea I should have read forward through all your replies before
>> responding to the first one but I think it clarified things as you point
>> out here. We appreciate you help and suggestions.
>>
> 
> OK, so I have a solution that does not require kernel_info at a fixed offset:
> 
> - put this at the end of arch/x86/boot/compressed/vmlinux.lds.S
> 
> #ifdef CONFIG_SECURE_LAUNCH
> PROVIDE(kernel_info_offset      = ABSOLUTE(kernel_info - startup_32));
> PROVIDE(mle_header_offset       = kernel_info_offset +
> ABSOLUTE(mle_header - startup_32));
> PROVIDE(sl_stub_entry_offset    = kernel_info_offset +
> ABSOLUTE(sl_stub_entry - startup_32));
> PROVIDE(_edata_offset           = kernel_info_offset + ABSOLUTE(_edata
> - startup_32));
> #endif
> 
> 
> and use this for the header fields:
> 
>          /* Offset to the MLE header structure */
> #if IS_ENABLED(CONFIG_SECURE_LAUNCH)
>          .long   mle_header_offset - kernel_info
> #else
>          .long   0
> #endif
> 

Awesome thank you! We will work on incorporating this unless someone 
else sees a problem with it (or we run into problems and need to revisit).

Ross

> 
> 
> SYM_DATA_START(mle_header)
>          .long   0x9082ac5a  /* UUID0 */
>          .long   0x74a7476f  /* UUID1 */
>          .long   0xa2555c0f  /* UUID2 */
>          .long   0x42b651cb  /* UUID3 */
>          .long   0x00000034  /* MLE header size */
>          .long   0x00020002  /* MLE version 2.2 */
>          .long   sl_stub_entry_offset - kernel_info /* Linear entry
> point of MLE (virt. address) */
>          .long   0x00000000  /* First valid page of MLE */
>          .long   0x00000000  /* Offset within binary of first byte of MLE */
>          .long   _edata_offset - kernel_info /* Offset within binary of
> last byte + 1 of MLE */
>          .long   0x00000227  /* Bit vector of MLE-supported capabilities */
>          .long   0x00000000  /* Starting linear address of command line
> (unused) */
>          .long   0x00000000  /* Ending linear address of command line (unused) */
>