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

From: Ard Biesheuvel
Date: Fri May 31 2024 - 10:04:37 EST

On Fri, 31 May 2024 at 15:33, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Fri, 31 May 2024 at 13:00, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> >
> > Hello Ross,
> >
> > On Fri, 31 May 2024 at 03:32, Ross Philipson <ross.philipson@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > > 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://www.intel.com/content/dam/www/public/us/en/documents/guides/intel-txt-software-development-guide.pdf
> > > +
> > >
> >
> > 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.

OK, so instead of patch #1, please use the linker script to generate
these constants.

I.e., add this to arch/x86/boot/compressed/vmlinux.lds.S

#ifdef CONFIG_SECURE_LAUNCH
PROVIDE(mle_header_offset = mle_header - startup_32);
PROVIDE(sl_stub_entry_offset = sl_stub_entry - startup_32);
PROVIDE(_edata_offset = _edata - startup_32);
#endif

and use the symbols on the left hand side in the code.