smm: Replace SMI assembler code with C code.

Convert the SMI handler from assembly to C.  This makes the handler
easier to understand and enhance.

The new handler will use references to the reserved memory at
0xf0000-0x100000.  If the physical memory in that range is modified at
runtime, then the SMI handler will cease to function properly (and may
allow unintended code to run in SMM mode).  However, that area is
marked as reserved and is normally made read-only at runtime, so there
is little risk in relying on it.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 30 insertions, 39 deletions

diff --git a/src/fw/smm.c b/src/fw/smm.c
index f486c78..3d0caa1 100644
--- a/src/fw/smm.c
+++ b/src/fw/smm.c
@@ -1,6 +1,6 @@
 // System Management Mode support (on emulators)
 //
-// Copyright (C) 2008  Kevin O'Connor <kevin@koconnor.net>
+// Copyright (C) 2008-2014  Kevin O'Connor <kevin@koconnor.net>
 // Copyright (C) 2006 Fabrice Bellard
 //
 // This file may be distributed under the terms of the GNU LGPLv3 license.
@@ -17,47 +17,39 @@
 #include "util.h" // smm_setup
 #include "x86.h" // wbinvd
 
-extern u8 smm_code_start, smm_code_end;
-
-ASM32FLAT(
-    ".global smm_code_start, smm_code_end\n"
-    "  .code16gcc\n"
-    "smm_code_start:\n"
-    "  mov %cs, %ax\n"
-    "  cmp $0xa000, %ax\n"
-    "  je smm_exit\n"
-
-    /* code to relocate SMBASE to 0xa0000 */
-    "  movl $" __stringify(BUILD_SMM_INIT_ADDR) " + 0x7efc, %ebx\n"
-    "  addr32 movb (%ebx), %al\n"  /* revision ID to see if x86_64 or x86 */
-    "  cmpb $0x64, %al\n"
-    "  je 1f\n"
-    "  movl $" __stringify(BUILD_SMM_INIT_ADDR) " + 0x7ef8, %ebx\n"
-    "  jmp 2f\n"
-    "1:\n"
-    "  movl $" __stringify(BUILD_SMM_INIT_ADDR) " + 0x7f00, %ebx\n"
-    "2:\n"
-    "  movl $" __stringify(BUILD_SMM_ADDR) " - 0x8000, %eax\n"
-    "  addr32 movl %eax, (%ebx)\n"
-    /* indicate to the BIOS that the SMM code was executed */
-    "  movb $0x00, %al\n"
-    "  movw $" __stringify(PORT_SMI_STATUS) ", %dx\n"
-    "  outb %al, %dx\n"
-    "smm_exit:\n"
-    "  rsm\n"
-    "smm_code_end:\n"
-    "  .code32\n"
-    );
+void VISIBLE32FLAT
+handle_smi(u16 cs)
+{
+    u8 cmd = inb(PORT_SMI_CMD);
+    dprintf(DEBUG_HDL_smi, "handle_smi cmd=%x cs=%x\n", cmd, cs);
+
+    void *smbase = MAKE_FLATPTR(cs, 0) + 0x8000;
+    if (smbase == (void*)BUILD_SMM_INIT_ADDR) {
+        // relocate SMBASE to 0xa0000
+        u8 *smrev = smbase + 0x7efc;
+        u32 *newbase = smbase + 0x7ef8;
+        if (*smrev == 0x64)
+            newbase = smbase + 0x7f00;
+        *newbase = BUILD_SMM_ADDR - 0x8000;
+        // indicate to smm_relocate_and_restore() that the SMM code was executed
+        outb(0x00, PORT_SMI_STATUS);
+        return;
+    }
+}
+
+extern void entry_smi(void);
+// movw %cs, %ax; ljmpw $SEG_BIOS, $(entry_smi - BUILD_BIOS_ADDR)
+#define SMI_INSN (0xeac88c | ((u64)SEG_BIOS<<40) \
+                  | ((u64)((u32)entry_smi - BUILD_BIOS_ADDR) << 24))
 
 static void
 smm_save_and_copy(void)
 {
-    /* save original memory content */
+    // save original memory content
     memcpy((void *)BUILD_SMM_ADDR, (void *)BUILD_SMM_INIT_ADDR, BUILD_SMM_SIZE);
 
-    /* copy the SMM code, which will relocate itself on the first execution */
-    memcpy((void *)BUILD_SMM_INIT_ADDR, &smm_code_start,
-           &smm_code_end - &smm_code_start);
+    // Setup code entry point.
+    *(u64*)BUILD_SMM_INIT_ADDR = SMI_INSN;
 }
 
 static void
@@ -76,9 +68,8 @@ smm_relocate_and_restore(void)
     /* restore original memory content */
     memcpy((void *)BUILD_SMM_INIT_ADDR, (void *)BUILD_SMM_ADDR, BUILD_SMM_SIZE);
 
-    /* copy the SMM code */
-    memcpy((void *)BUILD_SMM_ADDR, &smm_code_start
-           , &smm_code_end - &smm_code_start);
+    // Setup code entry point.
+    *(u64*)BUILD_SMM_ADDR = SMI_INSN;
     wbinvd();
 }