KernelTestFramework#6 support exception tables

Signed-off-by: Daniele Ahmed <[email protected]>

arch/x86/link.ld

@@ -170,6 +170,14 @@ SECTIONS
         __end_data = .;
     } :kernel
 
+    .extables BLOCK(4K) : ALIGN(4K)
+    {
+        __start_extables = .;
+            *(.extables)
+        . = ALIGN(4K);
+        __end_extables = .;
+    } :kernel
+
     .bss BLOCK(4K) : ALIGN(4K)
     {
         . = ALIGN(4K);

arch/x86/traps.c

@@ -28,6 +28,8 @@
 #include <drivers/keyboard.h>
 #include <drivers/pit.h>
 #include <drivers/serial.h>
+#include <extables.h>
+#include <mm/regions.h>
 #include <ktf.h>
 #include <lib.h>
 #include <percpu.h>
@@ -289,6 +291,24 @@ void print_callstack(const void *sp, const void *ip) {
 
 void do_exception(struct cpu_regs *regs) {
     static char ec_str[32], panic_str[128];
+    for (extable_entry_t *cur = __start_extables; cur < __end_extables; ++cur) {
+        if (regs->_ASM_IP == cur->fault_addr) {
+            printk("found exception entry\n");
+            if (cur->fixup) {
+                printk("using fixup\n");
+                regs->_ASM_IP = cur->fixup;
+            }
+            if (cur->cb) {
+                printk("using cb\n");
+                cur->cb(regs);
+            }
+            if (cur->fixup || cur->cb) {
+                return;
+            } else {
+                panic("fixup or cb must be set in the extable_entry\n");
+            }
+        }
+    }
 
     dump_regs(regs);
     print_callstack(_ptr(regs->_ASM_SP), _ptr(regs->_ASM_IP));

include/extables.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright © 2021 Amazon.com, Inc. or its affiliates.
+ * All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#ifndef KTF_EXTABLES_H
+#define KTF_EXTABLES_H
+
+#include <arch/x86/processor.h>
+
+typedef void(extable_entry_callback_t)(cpu_regs_t *regs);
+
+struct extable_entry {
+    uint64_t fault_addr;
+
+    uint64_t fixup;
+    extable_entry_callback_t *cb;
+};
+typedef struct extable_entry extable_entry_t;
+
+#define ASM_EXTABLE_HANDLER(fault_address, fixup, handler)             \
+    ".pushsection .extables, \"a\";\n"                          \
+    ".quad " STR(fault_address) ", " STR(fixup) ", " STR(handler) ";\n"    \
+    ".popsection;\n"
+
+#endif
+

include/lib.h

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2020 Amazon.com, Inc. or its affiliates.
+ * Copyright © 2021 Amazon.com, Inc. or its affiliates.
  * All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -28,6 +28,7 @@
 #include <asm-macros.h>
 #include <console.h>
 #include <ktf.h>
+#include <extables.h>
 #include <processor.h>
 #include <segment.h>
 
@@ -144,6 +145,25 @@ static inline uint64_t rdmsr(uint32_t msr_idx) {
     return (((uint64_t) high) << 32) | low;
 }
 
+/*
+ * read the msr_idx msr; the result is valid iff *read is true
+ */
+static inline uint64_t rdmsr_safe(uint32_t msr_idx, bool *read) {
+    uint32_t low, high;
+    low = high = 0;
+
+    *read = false;
+
+    //asm("1: rdmsr; 2: ret;"
+    asm volatile("1: ret; 2: ret;"
+        ASM_EXTABLE_HANDLER(1b, 2b, 0)
+        //: "=a"(low), "=d"(high) : "c"(msr_idx)
+    );
+
+    *read = true;
+    return (((uint64_t) high) << 32) | low;
+}
+
 static inline void wrmsr(uint32_t msr_idx, uint64_t value) {
     asm volatile("wrmsr" ::"c"(msr_idx), "a"((uint32_t) value),
                  "d"((uint32_t)(value >> 32)));

include/mm/regions.h

@@ -38,6 +38,7 @@
 
 #ifndef __ASSEMBLY__
 #include <cmdline.h>
+#include <extables.h>
 #include <page.h>
 #include <string.h>
 
@@ -56,6 +57,7 @@ extern unsigned long __start_bss_init[], __end_bss_init[];
 
 extern unsigned long __start_text_rmode[], __end_text_rmode[];
 extern unsigned long __start_data_rmode[], __end_data_rmode[];
+extern struct extable_entry __start_extables[], __end_extables[];
 extern unsigned long __start_bss_rmode[], __end_bss_rmode[];
 
 extern struct ktf_param __start_cmdline[], __end_cmdline[];

mm/regions.c

@@ -60,6 +60,7 @@ addr_range_t addr_ranges[] = {
 
     KERNEL_RANGE( ".text",      L1_PROT_RO,      __start_text,           __end_text      ),
     KERNEL_RANGE( ".data",      L1_PROT,         __start_data,           __end_data      ),
+    KERNEL_RANGE( ".extables",  L1_PROT_RO,      __start_extables,       __end_extables  ),
     KERNEL_RANGE( ".bss",       L1_PROT,         __start_bss,            __end_bss       ),
     KERNEL_RANGE( ".rodata",    L1_PROT_RO,      __start_rodata,         __end_rodata    ),
     KERNEL_RANGE( ".symbols",   L1_PROT_RO,      __start_symbols,        __end_symbols   ),

tests/test.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020 Amazon.com, Inc. or its affiliates.
+ * Copyright (c) 2021 Amazon.com, Inc. or its affiliates.
  * All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -64,8 +64,11 @@ void test_main(void) {
     test_fn *fn = NULL;
     unsigned n = 0;
 
-    printk("\nRunning tests\n");
+    bool read = false;
+    rdmsr_safe(0, &read);
+    printk("\nread? %x\n", read);
 
+    printk("\nRunning tests\n");
     while (get_next_test(&fn, &name) == TESTS_FOUND) {
         int rc;