Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7457c0da authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

x86/alternatives: Add int3_emulate_call() selftest 



Given that the entry_*.S changes for this functionality are somewhat
tricky, make sure the paths are tested every boot, instead of on the
rare occasion when we trip an INT3 while rewriting text.

Requested-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent faeedb06

arch/x86/kernel/alternative.c

+77 −4
Original line number Original line Diff line number Diff line
@@ -615,11 +615,83 @@ extern struct paravirt_patch_site __start_parainstructions[], 
	__stop_parainstructions[];

	__stop_parainstructions[];

#endif	/* CONFIG_PARAVIRT */

#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.

 */

static void __init int3_magic(unsigned int *ptr)

{

	*ptr = 1;

}



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_SEL_RAW(a, D) (&val) : "memory");



	BUG_ON(val != 1);



	unregister_die_notifier(&int3_exception_nb);

}



void __init alternative_instructions(void)

void __init alternative_instructions(void)

{

{

	/* The patching is not fully atomic, so try to avoid local interruptions

	int3_selftest();

	   that might execute the to be patched code.



	   Other CPUs are not running. */

	/*

	 * 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();

	stop_nmi();





	/*

	/*
@@ -644,10 +716,11 @@ void __init alternative_instructions(void) 
					    _text, _etext);

					    _text, _etext);

	}

	}





	if (!uniproc_patched || num_possible_cpus() == 1)

	if (!uniproc_patched || num_possible_cpus() == 1) {

		free_init_pages("SMP alternatives",

		free_init_pages("SMP alternatives",

				(unsigned long)__smp_locks,

				(unsigned long)__smp_locks,

				(unsigned long)__smp_locks_end);

				(unsigned long)__smp_locks_end);

	}

#endif

#endif





	apply_paravirt(__parainstructions, __parainstructions_end);

	apply_paravirt(__parainstructions, __parainstructions_end);