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-rw-r--r--arch/x86/kernel/alternative.c96
1 files changed, 92 insertions, 4 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 390596b761e3..16f36f60a394 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -615,11 +615,98 @@ extern struct paravirt_patch_site __start_parainstructions[],
__stop_parainstructions[];
#endif /* CONFIG_PARAVIRT */
+/*
+ * Self-test for the INT3 based CALL emulation code.
+ *
+ * This exercises int3_emulate_call() to make sure INT3 pt_regs are set up
+ * properly and that there is a stack gap between the INT3 frame and the
+ * previous context. Without this gap doing a virtual PUSH on the interrupted
+ * stack would corrupt the INT3 IRET frame.
+ *
+ * See entry_{32,64}.S for more details.
+ */
+
+/*
+ * We define the int3_magic() function in assembly to control the calling
+ * convention such that we can 'call' it from assembly.
+ */
+
+extern void int3_magic(unsigned int *ptr); /* defined in asm */
+
+asm (
+" .pushsection .init.text, \"ax\", @progbits\n"
+" .type int3_magic, @function\n"
+"int3_magic:\n"
+" movl $1, (%" _ASM_ARG1 ")\n"
+" ret\n"
+" .size int3_magic, .-int3_magic\n"
+" .popsection\n"
+);
+
+extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
+
+static int __init
+int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
+{
+ struct die_args *args = data;
+ struct pt_regs *regs = args->regs;
+
+ if (!regs || user_mode(regs))
+ return NOTIFY_DONE;
+
+ if (val != DIE_INT3)
+ return NOTIFY_DONE;
+
+ if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip)
+ return NOTIFY_DONE;
+
+ int3_emulate_call(regs, (unsigned long)&int3_magic);
+ return NOTIFY_STOP;
+}
+
+static void __init int3_selftest(void)
+{
+ static __initdata struct notifier_block int3_exception_nb = {
+ .notifier_call = int3_exception_notify,
+ .priority = INT_MAX-1, /* last */
+ };
+ unsigned int val = 0;
+
+ BUG_ON(register_die_notifier(&int3_exception_nb));
+
+ /*
+ * Basically: int3_magic(&val); but really complicated :-)
+ *
+ * Stick the address of the INT3 instruction into int3_selftest_ip,
+ * then trigger the INT3, padded with NOPs to match a CALL instruction
+ * length.
+ */
+ asm volatile ("1: int3; nop; nop; nop; nop\n\t"
+ ".pushsection .init.data,\"aw\"\n\t"
+ ".align " __ASM_SEL(4, 8) "\n\t"
+ ".type int3_selftest_ip, @object\n\t"
+ ".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t"
+ "int3_selftest_ip:\n\t"
+ __ASM_SEL(.long, .quad) " 1b\n\t"
+ ".popsection\n\t"
+ : ASM_CALL_CONSTRAINT
+ : __ASM_SEL_RAW(a, D) (&val)
+ : "memory");
+
+ BUG_ON(val != 1);
+
+ unregister_die_notifier(&int3_exception_nb);
+}
+
void __init alternative_instructions(void)
{
- /* The patching is not fully atomic, so try to avoid local interruptions
- that might execute the to be patched code.
- Other CPUs are not running. */
+ int3_selftest();
+
+ /*
+ * The patching is not fully atomic, so try to avoid local
+ * interruptions that might execute the to be patched code.
+ * Other CPUs are not running.
+ */
stop_nmi();
/*
@@ -644,10 +731,11 @@ void __init alternative_instructions(void)
_text, _etext);
}
- if (!uniproc_patched || num_possible_cpus() == 1)
+ if (!uniproc_patched || num_possible_cpus() == 1) {
free_init_pages("SMP alternatives",
(unsigned long)__smp_locks,
(unsigned long)__smp_locks_end);
+ }
#endif
apply_paravirt(__parainstructions, __parainstructions_end);