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stackprotector: remove self-test

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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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2008-07-13 21:42:44 +02:00
parent af9ff7868f
commit 4f962d4d65
1 changed files with 0 additions and 47 deletions
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47
kernel/panic.c
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@ -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