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Date: Tue, 4 Jun 2024 19:27:53 +0200 From: Ard Biesheuvel <ardb@...nel.org> To: ross.philipson@...cle.com Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org, kexec@...ts.infradead.org, linux-efi@...r.kernel.org, iommu@...ts.linux-foundation.org, dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com, dave.hansen@...ux.intel.com, mjg59@...f.ucam.org, James.Bottomley@...senpartnership.com, peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca, luto@...capital.net, nivedita@...m.mit.edu, herbert@...dor.apana.org.au, davem@...emloft.net, corbet@....net, ebiederm@...ssion.com, dwmw2@...radead.org, baolu.lu@...ux.intel.com, kanth.ghatraju@...cle.com, andrew.cooper3@...rix.com, trenchboot-devel@...glegroups.com Subject: Re: [PATCH v9 08/19] x86: Secure Launch kernel early boot stub On Tue, 4 Jun 2024 at 19:24, <ross.philipson@...cle.com> wrote: > > On 5/31/24 6:33 AM, Ard Biesheuvel wrote: > > On Fri, 31 May 2024 at 13:00, Ard Biesheuvel <ardb@...nel.org> wrote: > >> > >> Hello Ross, > >> > >> On Fri, 31 May 2024 at 03:32, Ross Philipson <ross.philipson@...cle.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@...cle.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.
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