Re: [PATCH v6 09/14] x86: Secure Launch SMP bringup support

[Jarkko Sakkinen]

On Thu May 4, 2023 at 5:50 PM EEST, Ross Philipson wrote:
> On Intel, the APs are left in a well documented state after TXT performs
> the late launch. Specifically they cannot have #INIT asserted on them so
> a standard startup via INIT/SIPI/SIPI cannot be performed. Instead the
> early SL stub code parked the APs in a pause/jmp loop waiting for an NMI.
> The modified SMP boot code is called for the Secure Launch case. The
> jump address for the RM piggy entry point is fixed up in the jump where
> the APs are waiting and an NMI IPI is sent to the AP. The AP vectors to
> the Secure Launch entry point in the RM piggy which mimics what the real
> mode code would do then jumps to the standard RM piggy protected mode
> entry point.
>
> Signed-off-by: Ross Philipson <ross.philipson@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/realmode.h      |  3 ++
>  arch/x86/kernel/smpboot.c            | 86 ++++++++++++++++++++++++++++++++++++
>  arch/x86/realmode/rm/header.S        |  3 ++
>  arch/x86/realmode/rm/trampoline_64.S | 37 ++++++++++++++++
>  4 files changed, 129 insertions(+)
>
> diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
> index f6a1737..576fe62 100644
> --- a/arch/x86/include/asm/realmode.h
> +++ b/arch/x86/include/asm/realmode.h
> @@ -38,6 +38,9 @@ struct real_mode_header {
>  #ifdef CONFIG_X86_64
>  	u32	machine_real_restart_seg;
>  #endif
> +#ifdef CONFIG_SECURE_LAUNCH
> +	u32	sl_trampoline_start32;
> +#endif

Cool I was implementing this relocatable realmode blob back in 2012 :-)

>  };
>  
>  /* This must match data at realmode/rm/trampoline_{32,64}.S */
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 352f0ce..07d740be 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -57,6 +57,7 @@
>  #include <linux/pgtable.h>
>  #include <linux/overflow.h>
>  #include <linux/stackprotector.h>
> +#include <linux/slaunch.h>
>  
>  #include <asm/acpi.h>
>  #include <asm/cacheinfo.h>
> @@ -1068,6 +1069,83 @@ int common_cpu_up(unsigned int cpu, struct task_struct *idle)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_SECURE_LAUNCH
> +
> +static atomic_t first_ap_only = {1};

This should be documented.

> +
> +/*
> + * Called to fix the long jump address for the waiting APs to vector to
> + * the correct startup location in the Secure Launch stub in the rmpiggy.
> + */
> +static int
> +slaunch_fixup_jump_vector(void)

Please put the same line.

> +{
> +	struct sl_ap_wake_info *ap_wake_info;
> +	u32 *ap_jmp_ptr = NULL;
> +
> +	if (!atomic_dec_and_test(&first_ap_only))
> +		return 0;
> +
> +	ap_wake_info = slaunch_get_ap_wake_info();
> +
> +	ap_jmp_ptr = (u32 *)__va(ap_wake_info->ap_wake_block +
> +				 ap_wake_info->ap_jmp_offset);
> +
> +	*ap_jmp_ptr = real_mode_header->sl_trampoline_start32;
> +
> +	pr_debug("TXT AP long jump address updated\n");
> +
> +	return 0;
> +}
> +
> +/*
> + * TXT AP startup is quite different than normal. The APs cannot have #INIT
> + * asserted on them or receive SIPIs. The early Secure Launch code has parked
> + * the APs in a pause loop waiting to receive an NMI. This will wake the APs
> + * and have them jump to the protected mode code in the rmpiggy where the rest
> + * of the SMP boot of the AP will proceed normally.
> + */
> +static int
> +slaunch_wakeup_cpu_from_txt(int cpu, int apicid)

Ditto.


> +{
> +	unsigned long send_status = 0, accept_status = 0;

I would put these to separate lines. Maybe a matter of taste but
it is easier to spot initializations.

> +
> +	/* Only done once */
> +	if (slaunch_fixup_jump_vector())
> +		return -1;
> +
> +	/* Send NMI IPI to idling AP and wake it up */
> +	apic_icr_write(APIC_DM_NMI, apicid);
> +
> +	if (init_udelay == 0)
> +		udelay(10);
> +	else
> +		udelay(300);
> +
> +	send_status = safe_apic_wait_icr_idle();
> +
> +	if (init_udelay == 0)
> +		udelay(10);
> +	else
> +		udelay(300);

Magic numbers and no inline comment.

> +
> +	accept_status = (apic_read(APIC_ESR) & 0xEF);
> +
> +	if (send_status)
> +		pr_err("Secure Launch IPI never delivered???\n");
> +	if (accept_status)
> +		pr_err("Secure Launch IPI delivery error (%lx)\n",
> +			accept_status);
> +
> +	return (send_status | accept_status);
> +}
> +
> +#else
> +
> +#define slaunch_wakeup_cpu_from_txt(cpu, apicid)	0
> +
> +#endif  /* !CONFIG_SECURE_LAUNCH */
> +
>  /*
>   * NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
>   * (ie clustered apic addressing mode), this is a LOGICAL apic ID.
> @@ -1132,6 +1210,13 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
>  	cpumask_clear_cpu(cpu, cpu_initialized_mask);
>  	smp_mb();
>  
> +	/* With Intel TXT, the AP startup is totally different */
> +	if ((slaunch_get_flags() & (SL_FLAG_ACTIVE|SL_FLAG_ARCH_TXT)) ==
> +	   (SL_FLAG_ACTIVE|SL_FLAG_ARCH_TXT)) {
> +		boot_error = slaunch_wakeup_cpu_from_txt(cpu, apicid);
> +		goto txt_wake;
> +	}
> +
>  	/*
>  	 * Wake up a CPU in difference cases:
>  	 * - Use a method from the APIC driver if one defined, with wakeup
> @@ -1147,6 +1232,7 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
>  		boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
>  						     cpu0_nmi_registered);
>  
> +txt_wake:
>  	if (!boot_error) {
>  		/*
>  		 * Wait 10s total for first sign of life from AP
> diff --git a/arch/x86/realmode/rm/header.S b/arch/x86/realmode/rm/header.S
> index 2eb62be..3b5cbcb 100644
> --- a/arch/x86/realmode/rm/header.S
> +++ b/arch/x86/realmode/rm/header.S
> @@ -37,6 +37,9 @@ SYM_DATA_START(real_mode_header)
>  #ifdef CONFIG_X86_64
>  	.long	__KERNEL32_CS
>  #endif
> +#ifdef CONFIG_SECURE_LAUNCH
> +	.long	pa_sl_trampoline_start32
> +#endif
>  SYM_DATA_END(real_mode_header)
>  
>  	/* End signature, used to verify integrity */
> diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
> index e38d61d..8bb4b0d 100644
> --- a/arch/x86/realmode/rm/trampoline_64.S
> +++ b/arch/x86/realmode/rm/trampoline_64.S
> @@ -104,6 +104,43 @@ SYM_CODE_END(sev_es_trampoline_start)
>  
>  	.section ".text32","ax"
>  	.code32
> +#ifdef CONFIG_SECURE_LAUNCH
> +	.balign 4
> +SYM_CODE_START(sl_trampoline_start32)
> +	/*
> +	 * The early secure launch stub AP wakeup code has taken care of all
> +	 * the vagaries of launching out of TXT. This bit just mimics what the
> +	 * 16b entry code does and jumps off to the real startup_32.
> +	 */
> +	cli
> +	wbinvd
> +
> +	/*
> +	 * The %ebx provided is not terribly useful since it is the physical
> +	 * address of tb_trampoline_start and not the base of the image.
> +	 * Use pa_real_mode_base, which is fixed up, to get a run time
> +	 * base register to use for offsets to location that do not have
> +	 * pa_ symbols.
> +	 */
> +	movl    $pa_real_mode_base, %ebx
> +
> +	/*
> +	 * This may seem a little odd but this is what %esp would have had in
> +	 * it on the jmp from real mode because all real mode fixups were done
> +	 * via the code segment. The base is added at the 32b entry.
> +	 */
> +	movl	rm_stack_end, %esp
> +
> +	lgdt    tr_gdt(%ebx)
> +	lidt    tr_idt(%ebx)
> +
> +	movw	$__KERNEL_DS, %dx	# Data segment descriptor
> +
> +	/* Jump to where the 16b code would have jumped */
> +	ljmpl	$__KERNEL32_CS, $pa_startup_32
> +SYM_CODE_END(sl_trampoline_start32)
> +#endif
> +
>  	.balign 4
>  SYM_CODE_START(startup_32)
>  	movl	%edx, %ss
> -- 
> 1.8.3.1


The trampoline_64.S changes look reasonable to me (with a quick look).

BR, Jarkko