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

@@ -351,10 +351,12 @@ cs32_switch:
         jmp     *%edi
 
         /*
-         * Entry point for TrenchBoot Secure Launch on Intel TXT platforms.
+         * Entry point for TrenchBoot Secure Launch, common for Intel TXT and
+         * AMD Secure Startup, but state is slightly different.
          *
+         * On Intel:
          * CPU is in 32b protected mode with paging disabled. On entry:
-         * - %ebx = %eip = MLE entry point,
+         * - %ebx = %eip = this entry point,
          * - stack pointer is undefined,
          * - CS is flat 4GB code segment,
          * - DS, ES, SS, FS and GS are undefined.
@@ -368,13 +370,34 @@ cs32_switch:
          * - trying to enter real mode results in reset
          * - APs must be brought up by MONITOR or GETSEC[WAKEUP], depending on
          *   which is supported by a given SINIT ACM
+         *
+         * On AMD (as implemented by TrenchBoot's SKL):
+         * CPU is in 32b protected mode with paging disabled. On entry:
+         * - %ebx = %eip = this entry point,
+         * - %ebp holds base address of SKL
+         * - stack pointer is treated as undefined for parity with TXT,
+         * - CS is flat 4GB code segment,
+         * - DS, ES, SS are flat 4GB data segments, but treated as undefined for
+         *   parity with TXT.
+         *
+         * Additional restrictions:
+         * - interrupts (including NMIs and SMIs) are disabled and must be
+         *   enabled later
+         * - APs must be brought up by SIPI without an INIT
          */
 slaunch_stub_entry:
         /* Calculate the load base address. */
         mov     %ebx, %esi
         sub     $sym_offs(slaunch_stub_entry), %esi
 
-        /* Mark Secure Launch boot protocol and jump to common entry. */
+        /* On AMD, %ebp holds the base address of SLB, save it for later. */
+        mov     %ebp, %ebx
+
+        /*
+         * Mark Secure Launch boot protocol and jump to common entry. Note that
+         * all general purpose registers except %ebx and %esi are clobbered
+         * between here and .Lslaunch_proto.
+         */
         mov     $SLAUNCH_BOOTLOADER_MAGIC, %eax
         jmp     .Lset_stack
 
@@ -497,10 +520,12 @@ __start:
         sub     $8, %esp
 
         push    %esp                             /* pointer to output structure */
+        push    %ebx                             /* Slaunch parameter on AMD */
         lea     sym_offs(__2M_rwdata_end), %ecx  /* end of target image */
         lea     sym_offs(_start), %edx           /* target base address */
         mov     %esi, %eax                       /* load base address */
-        /* slaunch_early_tests(load/eax, tgt/edx, tgt_end/ecx, ret/stk) using fastcall. */
+        /* slaunch_early_tests(load/eax, tgt/edx, tgt_end/ecx,
+                               slaunch/stk, ret/stk) using fastcall. */
         call    slaunch_early_tests
 
         /* Move outputs of slaunch_early_tests() from stack into registers. */

xen/arch/x86/boot/slaunch_early.c

@@ -18,13 +18,30 @@
 #include <xen/macros.h>
 #include <xen/types.h>
 #include <asm/intel_txt.h>
+#include <xen/slr_table.h>
+#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,
@@ -104,13 +121,43 @@ static void verify_pmr_ranges(struct txt_os_mle_data *os_mle,
 void slaunch_early_tests(uint32_t load_base_addr,
                          uint32_t tgt_base_addr,
                          uint32_t tgt_end_addr,
+                         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.
+         */
+        struct slr_table *slrt;
+        struct slr_entry_dl_info *dl_info;
+
+        const uint16_t *sl_header = (void *)slaunch_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];
+        slrt = (struct slr_table *)result->slrt_pa;
+
+        result->mbi_pa = 0;
+        dl_info = (struct slr_entry_dl_info *)
+                  slr_next_entry_by_tag (slrt, NULL, SLR_ENTRY_DL_INFO);
+        /* Basic checks only, SKL checked and consumed the rest. */
+        if ( dl_info                             == NULL
+             || dl_info->hdr.size                != sizeof(*dl_info)
+             || dl_info->bl_context.bootloader   != SLR_BOOTLOADER_GRUB )
+            result->mbi_pa = dl_info->bl_context.context;
+
+        return;
+    }
+
     /* Clear the TXT error registers for a clean start of day */
     write_txt_reg(TXTCR_ERRORCODE, 0);