The "ground truth" stack protector cookie value is kept in a global
variable, and loaded in every function prologue and epilogue to store
it into resp. compare it with the stack slot holding the cookie.
If the comparison fails, the program aborts, and this might occur
spuriously when the global variable changes values between the entry and
exit of a function. This implies that assigning the global variable at
boot should not involve any instrumented function calls, unless special
care is taken to ensure that the live call stack is synchronized, which
is non-trivial.
So avoid any function calls, including grub_memcpy(), which is
unnecessary given that the stack cookie is always a suitably aligned
variable of the native word size.
While at it, leave the last byte 0x0 to avoid inadvertent unbounded
strings on the stack.
Note that the use of __attribute__((optimize)) is described as
unsuitable for production use in the GCC documentation, so let's drop
this as well now that it is no longer needed.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
b272ed230e