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Commit 4f962d4d authored by Ingo Molnar's avatar Ingo Molnar
Browse files

stackprotector: remove self-test 



turns out gcc generates such stackprotector-failure sequences
in certain circumstances:

        movq    -8(%rbp), %rax  # D.16032,
        xorq    %gs:40, %rax    #,
        jne     .L17    #,
        leave
        ret
.L17:
        call    __stack_chk_fail        #
        .size   __stack_chk_test_func, .-__stack_chk_test_func
        .section        .init.text,"ax",@progbits
        .type   panic_setup, @function
panic_setup:
        pushq   %rbp    #

note that there's no jump back to the failing context after the
call to __stack_chk_fail - i.e. it has a ((noreturn)) attribute.

Which is fair enough in the normal case but kills the self-test.
(as we cannot reliably return in the self-test)

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent af9ff786

kernel/panic.c

+0 −47
Original line number Diff line number Diff line
@@ -329,62 +329,15 @@ EXPORT_SYMBOL(warn_on_slowpath); 
#warning You have selected the CONFIG_CC_STACKPROTECTOR option, but the gcc used does not support this.

#endif



static unsigned long __stack_check_testing;



/*

 * Self test function for the stack-protector feature.

 * This test requires that the local variable absolutely has

 * a stack slot.

 */

static noinline void __stack_chk_test_func(void)

{

	unsigned long dummy_buffer[64]; /* force gcc to use the canary */



	current->stack_canary = ~current->stack_canary;

	refresh_stack_canary();

	dummy_buffer[3] = 1; /* fool gcc into keeping the variable */

}



static int __stack_chk_test(void)

{

	printk(KERN_INFO "Testing -fstack-protector-all feature\n");

	__stack_check_testing = (unsigned long)&__stack_chk_test_func;

	__stack_chk_test_func();

	if (__stack_check_testing) {

		printk(KERN_ERR "-fstack-protector-all test failed\n");

		WARN_ON(1);

	};

	current->stack_canary = ~current->stack_canary;

	refresh_stack_canary();

	return 0;

}

/*

 * Called when gcc's -fstack-protector feature is used, and

 * gcc detects corruption of the on-stack canary value

 */

void __stack_chk_fail(void)

{

	if (__stack_check_testing == (unsigned long)&__stack_chk_test_func) {

		long delta;



		delta = (unsigned long)__builtin_return_address(0) -

				__stack_check_testing;

		/*

		 * The test needs to happen inside the test function, so

		 * check if the return address is close to that function.

		 * The function is only 2 dozen bytes long, but keep a wide

		 * safety margin to avoid panic()s for normal users regardless

		 * of the quality of the compiler.

		 */

		if (delta >= 0 && delta <= 400) {

			__stack_check_testing = 0;

			return;

		}

	}

	panic("stack-protector: Kernel stack is corrupted in: %p\n",

		__builtin_return_address(0));

}

EXPORT_SYMBOL(__stack_chk_fail);



late_initcall(__stack_chk_test);

#endif