Exception table support

arch/x86/extables.c

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 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.
+ */
+
+void init_extables(void) { /* no-op */
+}

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

@@ -28,8 +28,10 @@
 #include <drivers/keyboard.h>
 #include <drivers/pit.h>
 #include <drivers/serial.h>
+#include <extables.h>
 #include <ktf.h>
 #include <lib.h>
+#include <mm/regions.h>
 #include <percpu.h>
 #include <processor.h>
 #include <segment.h>
@@ -287,9 +289,30 @@ void print_callstack(const void *sp, const void *ip) {
     printk("\n");
 }
 
+static inline void use_extables(struct cpu_regs *regs) {
+    for (extable_entry_t *cur = __start_extables; cur < __end_extables; ++cur) {
+        if (regs->_ASM_IP == cur->fault_addr) {
+            if (cur->fixup) {
+                regs->_ASM_IP = cur->fixup;
+            }
+            if (cur->cb) {
+                cur->cb(regs);
+            }
+            if (cur->fixup || cur->cb) {
+                return;
+            }
+            else {
+                panic("fixup or cb must be set in the extable_entry\n");
+            }
+        }
+    }
+}
+
 void do_exception(struct cpu_regs *regs) {
     static char ec_str[32], panic_str[128];
 
+    use_extables(regs);
+
     dump_regs(regs);
     print_callstack(_ptr(regs->_ASM_SP), _ptr(regs->_ASM_IP));
 

common/setup.c

@@ -254,12 +254,12 @@ void __noreturn __text_init kernel_start(uint32_t multiboot_magic,
     if (opt_debug)
         dump_pagetables();
 
-    /* TODO: Exception tables */
-
     init_percpu();
 
     init_traps(get_bsp_cpu_id());
 
+    init_extables();
+
     init_slab();
 
     /* Try to initialize ACPI (and MADT) */

drivers/acpi/acpica/osl.c

@@ -207,11 +207,44 @@ void *AcpiOsAllocate(ACPI_SIZE Size) { return kmalloc(Size); }
 
 void AcpiOsFree(void *Memory) { kfree(Memory); }
 
-/* FIXME: Check if pages are mapped (with exception tables) */
-BOOLEAN AcpiOsReadable(void *Memory, ACPI_SIZE Length) { return true; }
+BOOLEAN AcpiOsReadable(void *Memory, ACPI_SIZE Length) {
+    volatile bool success = false;
+    char *mem;
+
+    for (mfn_t mfn = virt_to_mfn(Memory); mfn <= virt_to_mfn((char *) Memory + Length);
+         ++mfn) {
+        success = false;
+        mem = mfn_to_virt_kern(mfn);
+        asm volatile("1: movq ( %[mem] ), %%rax; movq $1, %[success];"
+                     "2:" ASM_EXTABLE(1b, 2b)
+                     : [ success ] "=m"(success)
+                     : [ mem ] "r"(mem)
+                     : "rax", "memory");
+        if (!success)
+            return false;
+    }
+    return success;
+}
 
-/* FIXME: Check if pages are mapped and writeable (with exception tables) */
-BOOLEAN AcpiOsWriteable(void *Memory, ACPI_SIZE Length) { return true; }
+BOOLEAN AcpiOsWriteable(void *Memory, ACPI_SIZE Length) {
+    volatile bool success = false;
+    char *mem;
+
+    for (mfn_t mfn = virt_to_mfn(Memory); mfn <= virt_to_mfn((char *) Memory + Length);
+         ++mfn) {
+        success = false;
+        mem = mfn_to_virt_kern(mfn);
+        asm volatile("1: orq $0, ( %[mem] ); movq $1, %[success];"
+                     "2:" ASM_EXTABLE(1b, 2b)
+                     : [ success ] "=m"(success), [ mem ] "=r"(mem)
+                     :
+                     : "memory");
+        if (!success)
+            return false;
+    }
+
+    return success;
+}
 
 void *AcpiOsMapMemory(ACPI_PHYSICAL_ADDRESS PhysicalAddress, ACPI_SIZE Length) {
     unsigned offset = PhysicalAddress & ~PAGE_MASK;

include/arch/x86/asm-macros.h

@@ -47,6 +47,9 @@
 
 #define PT_PADDR(table, shift) (((.- (table)) / PTE_SIZE) << (shift))
 
+#define PUSHSECTION(name) ".pushsection " STR(name) " ;\n"
+#define POPSECTION        ".popsection;\n"
+
 #ifdef __ASSEMBLY__
 
 /* clang-format off */

include/extables.h

@@ -0,0 +1,53 @@
+/*
+ * 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 {
+    x86_reg_t fault_addr;
+    x86_reg_t fixup;
+    extable_entry_callback_t cb;
+} __packed;
+typedef struct extable_entry extable_entry_t;
+
+#if defined(__x86_64__)
+#define ASM_EXTABLE_HANDLER(fault_address, fixup, handler)                               \
+    PUSHSECTION(.extables)                                                               \
+    ".quad " STR(fault_address) ", " STR(fixup) ", " STR(handler) ";\n" POPSECTION
+#else
+#define ASM_EXTABLE_HANDLER(fault_address, fixup, handler)                               \
+    PUSHSECTION(.extables)                                                               \
+    ".long " STR(fault_address) ", " STR(fixup) ", " STR(handler) ";\n" POPSECTION
+#endif
+
+#define ASM_EXTABLE(fault_address, fixup) ASM_EXTABLE_HANDLER(fault_address, fixup, 0)
+
+extern void init_extables(void);
+
+#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
@@ -434,4 +434,7 @@ extern void srand(unsigned s);
 
 extern int rand(void);
 
+extern bool wrmsr_safe(uint32_t msr_idx, uint64_t value);
+extern bool rdmsr_safe(uint32_t msr_idx, uint64_t *value);
+
 #endif /* KTF_LIB_H */

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[];

lib/lib.c

@@ -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
@@ -25,6 +25,8 @@
 #include <ktf.h>
 #include <lib.h>
 
+#include <extables.h>
+
 void __noreturn halt(void) {
     cli();
 
@@ -42,3 +44,33 @@ int rand(void) {
     seed = 6364136223846793005ULL * seed + 1;
     return seed >> 33;
 }
+
+/*
+ * read the msr_idx msr into value; the result is valid iff the returned value is true
+ */
+bool rdmsr_safe(uint32_t msr_idx, uint64_t *value) {
+    volatile bool success = false;
+    uint32_t low, high;
+
+    asm volatile("1: rdmsr; movb $1, %[success];"
+                 "2:" ASM_EXTABLE(1b, 2b)
+                 : "=a"(low), "=d"(high), [ success ] "=m"(success)
+                 : "c"(msr_idx)
+                 : "memory");
+    *value = (((uint64_t) high) << 32) | low;
+    return success;
+}
+
+/*
+ * write to the msr_idx msr; the result is valid iff the returned value is true
+ */
+bool wrmsr_safe(uint32_t msr_idx, uint64_t value) {
+    volatile bool success = false;
+
+    asm volatile("1: wrmsr; movq $1, %[success];"
+                 "2:" ASM_EXTABLE(1b, 2b)
+                 : [ success ] "=m"(success)
+                 : "c"(msr_idx), "a"((uint32_t) value), "d"((uint32_t)(value >> 32))
+                 : "memory");
+    return success;
+}

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   ),