Re: [PATCH v9 08/19] x86: Secure Launch kernel early boot stub

ross.philipson
2024-06-04T17:25:15Z

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?

Thank you,
Ross