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Commit 9c85f3bd authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
Browse files

x86/jump-label: Add safety checks to jump label conversions 



As with all modifying of kernel text, we need to be very paranoid.

When converting the jump label locations to and from nops to jumps
a check has been added to make sure what we are replacing is what we
expect, otherwise we bug.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 11570da1

arch/x86/kernel/jump_label.c

+28 −4
Original line number Diff line number Diff line
@@ -26,16 +26,40 @@ union jump_code_union { 


static void __jump_label_transform(struct jump_entry *entry,

				   enum jump_label_type type,

				   void *(*poker)(void *, const void *, size_t))

				   void *(*poker)(void *, const void *, size_t),

				   int init)

{

	union jump_code_union code;

	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];



	if (type == JUMP_LABEL_ENABLE) {

		/*

		 * We are enabling this jump label. If it is not a nop

		 * then something must have gone wrong.

		 */

		BUG_ON(memcmp((void *)entry->code, ideal_nop, 5) != 0);



		code.jump = 0xe9;

		code.offset = entry->target -

				(entry->code + JUMP_LABEL_NOP_SIZE);

	} else {

		/*

		 * We are disabling this jump label. If it is not what

		 * we think it is, then something must have gone wrong.

		 * If this is the first initialization call, then we

		 * are converting the default nop to the ideal nop.

		 */

		if (init) {

			const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };

			BUG_ON(memcmp((void *)entry->code, default_nop, 5) != 0);

		} else {

			code.jump = 0xe9;

			code.offset = entry->target -

				(entry->code + JUMP_LABEL_NOP_SIZE);

	} else

			BUG_ON(memcmp((void *)entry->code, &code, 5) != 0);

		}

		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);

	}



	(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);

}
@@ -45,7 +69,7 @@ void arch_jump_label_transform(struct jump_entry *entry, 
{

	get_online_cpus();

	mutex_lock(&text_mutex);

	__jump_label_transform(entry, type, text_poke_smp);

	__jump_label_transform(entry, type, text_poke_smp, 0);

	mutex_unlock(&text_mutex);

	put_online_cpus();

}
@@ -76,7 +100,7 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 
			jlstate = JL_STATE_NO_UPDATE;

	}

	if (jlstate == JL_STATE_UPDATE)

		__jump_label_transform(entry, type, text_poke_early);

		__jump_label_transform(entry, type, text_poke_early, 1);

}



#endif