Re: [PATCH v5 2/4] xen: common: add ability to enable stack protector

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Hi Julien,

Julien Grall <julien@xen.org> writes:

> Hi Volodymyr,
>
> On 13/02/2025 22:00, Volodymyr Babchuk wrote:
>> diff --git a/xen/common/stack-protector.c b/xen/common/stack-protector.c
>> new file mode 100644
>> index 0000000000..286753a1b1
>> --- /dev/null
>> +++ b/xen/common/stack-protector.c
>> @@ -0,0 +1,51 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +#include <xen/init.h>
>> +#include <xen/lib.h>
>> +#include <xen/random.h>
>> +#include <xen/time.h>
>> +
>> +/*
>> + * Initial value is chosen by a fair dice roll.
>> + * It will be updated during boot process.
>> + */
>> +#if BITS_PER_LONG == 32
>> +unsigned long __ro_after_init __stack_chk_guard = 0xdd2cc927UL;
>> +#else
>> +unsigned long __ro_after_init __stack_chk_guard = 0x2d853605a4d9a09cUL;
>> +#endif
>> +
>> +/*
>> + * This function should be called from early asm or from a C function
>> + * that escapes stack canary tracking (by calling
>> + * reset_stack_and_jump() for example).
>> + */
>> +void __init asmlinkage boot_stack_chk_guard_setup(void)
>
> I am probably missing something. But what prevent the compiler to
> insert a stack guard when entering this function and checking on exit?
> Wouldn't this fail because __stack_chk_guard would be different?

Yes, you are right. I got carried away a bit this time. It is working
right now only because GCC does not emit stack checking code in this
particular function. With "-fstack-protector-all" it panics, as expected.

> IOW, shouldn't this function be a static always inline like it used to be?

Yes, I am going to make it inline in the next version.


-- 
WBR, Volodymyr