x86/boot: find MBI and SLRT on AMD

secure-kernel-loader on AMD with SKINIT passes MBI as a parameter for
Multiboot kernel.

Another thing of interest is the location of SLRT which is bootloader's
data after SKL.

Signed-off-by: Sergii Dmytruk <[email protected]>

xen/arch/x86/boot/head.S

@@ -559,6 +559,8 @@ __start:
 
         /* Push arguments to stack and call slaunch_early_tests(). */
         push    %esp                        /* pointer to output structure */
+        push    %ebp                        /* Slaunch parameter on AMD */
+        push    %ebx                        /* Multiboot parameter */
         push    $sym_offs(__2M_rwdata_end)  /* end of target image */
         push    $sym_offs(_start)           /* target base address */
         push    %esi                        /* load base address */

xen/arch/x86/boot/slaunch_early.c

@@ -30,12 +30,33 @@ asm (
 #include "../include/asm/intel_txt.h"
 #include "../include/asm/slaunch.h"
 
+//#include "../../../tools/include/xen-tools/common-macros.h"
+#define __AC(X, Y)   (X ## Y)
+#define _AC(X, Y)    __AC(X, Y)
+
+#include "../include/asm/x86-vendors.h"
+
 struct early_tests_results
 {
     uint32_t mbi_pa;
     uint32_t slrt_pa;
 } __packed;
 
+static bool is_intel_cpu(void)
+{
+    /*
+     * asm/processor.h can't be included in early code, which means neither
+     * cpuid() function nor boot_cpu_data can be used here.
+     */
+    uint32_t eax, ebx, ecx, edx;
+    asm volatile ( "cpuid"
+          : "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx)
+          : "0" (0), "c" (0) );
+    return ebx == X86_VENDOR_INTEL_EBX
+        && ecx == X86_VENDOR_INTEL_ECX
+        && edx == X86_VENDOR_INTEL_EDX;
+}
+
 static void verify_pmr_ranges(struct txt_os_mle_data *os_mle,
                               struct txt_os_sinit_data *os_sinit,
                               uint32_t load_base_addr, uint32_t tgt_base_addr,
@@ -115,13 +136,32 @@ static void verify_pmr_ranges(struct txt_os_mle_data *os_mle,
 void __stdcall slaunch_early_tests(uint32_t load_base_addr,
                                    uint32_t tgt_base_addr,
                                    uint32_t tgt_end_addr,
+                                   uint32_t multiboot_param,
+                                   uint32_t slaunch_param,
                                    struct early_tests_results *result)
 {
     void *txt_heap;
     struct txt_os_mle_data *os_mle;
     struct txt_os_sinit_data *os_sinit;
     uint32_t size = tgt_end_addr - tgt_base_addr;
 
+    if ( !is_intel_cpu() )
+    {
+        /*
+         * Not an Intel CPU. Currently the only other option is AMD with SKINIT
+         * and secure-kernel-loader.
+         */
+
+        const uint16_t *sl_header = (void *)slaunch_param;
+        /* secure-kernel-loader passes MBI as a parameter for Multiboot
+         * kernel. */
+        result->mbi_pa = multiboot_param;
+        /* The fourth 16-bit integer of SKL's header is an offset to
+         * bootloader's data, which is SLRT. */
+        result->slrt_pa = slaunch_param + sl_header[3];
+        return;
+    }
+
     /* Clear the TXT error registers for a clean start of day */
     write_txt_reg(TXTCR_ERRORCODE, 0);